The "World Scientists' Warning to Humanity" was a document written in 1992 by Henry W. Kendall and signed by about 1,700 leading scientists. Twenty-five years later, in November 2017, 15,364 scientists signed "World Scientists' Warning to Humanity: A Second Notice" written by William J. Ripple and seven co-authors calling for, among other things, human population planning, and drastically diminishing per capita consumption of fossil fuels, meat, and other resources. The second notice has more scientist cosigners and formal supporters than any other journal article ever published.
First publication
In late 1992, the late Henry W. Kendall, a former chair of the board of directors of the Union of Concerned Scientists
(UCS), wrote the first warning, "World Scientists' Warning to
Humanity", which begins: "Human beings and the natural world are on a
collision course." A majority of the Nobel Prize laureates in the sciences signed the document; about 1,700 of the world's leading scientists appended their signature.
It was sometimes offered in opposition to the Heidelberg Appeal—also signed by numerous scientists and Nobel laureates earlier in 1992—which begins by criticizing "an irrational ideology which is opposed to scientific and industrial progress,
and impedes economic and social development." This document was often
cited by those who oppose theories relating to climate change.
In contrast, the UCS-led petition contains specific recommendations: "We must, for example, move away from fossil fuels to more benign, inexhaustible energy sources to cut greenhouse gasemissions and the pollution of our air and water. ... We must stabilize population."
Second Notice
In
November 2017, 15,364 scientists signed "World Scientists' Warning to
Humanity: A Second Notice" written by lead author professor of ecology, William J. Ripple of Oregon State University, along with 7 co-authors calling for, among other things, limiting population growth, and drastically diminishing per capita consumption of fossil fuels, meat, and other resources.
The second notice included 9 time-series graphs of key indicators, each
correlated to a specific issue mentioned in the original 1992 warning,
to show that most environmental issues are continuing to trend in the
wrong direction, most with no discernible change in rate. The article
included 13 specific steps humanity could take to transition to sustainability.
The second notice has more scientist cosigners and formal supporters than any other journal article ever published. The full warning was published in BioScience and it can still be endorsed on the Scientists Warning website.
2019 warning on climate change and 2021 and 2022 updates
In
November 2019, a group of more than 11,000 scientists from 153
countries named climate change an "emergency" that would lead to "untold
human suffering" if no big shifts in action take place:
We declare clearly and unequivocally that planet Earth is facing a climate emergency. To secure a sustainable
future, we must change how we live. [This] entails major
transformations in the ways our global society functions and interacts
with natural ecosystems.
The emergency declaration emphasized that economic growth and population growth "are among the most important drivers of increases in CO2
emissions from fossil fuel combustion" and that "we need bold and
drastic transformations regarding economic and population policies".
A 2021 update to the 2019 climate emergency declaration focuses
on 31 planetary vital signs (including greenhouse gases and temperature,
rising sea levels, energy use, ice mass, ocean heat content, Amazon
rainforest loss rate, etc), and recent changes to them. Of these, 18 are
reaching critical levels. The COVID-19 lockdowns,
which reduced transportation and consumption levels, had very little
impact on mitigating or reversing these trends. The authors say only
profound changes in human behavior can meet these challenges and
emphasize the need to move beyond the idea that global heating is a
stand alone emergency, and is one facet of the worsening environmental
crisis. This necessitates the need for transformational system changes
and to focus on the root cause of these crises, the vast human overexploitation of the earth, rather than just addressing symptom relief. They point to six areas where fundamental changes need to be made:
(1) energy — eliminating fossil fuels and shifting to renewables; (2) short-lived air pollutants — slashing black carbon (soot), methane, and hydrofluorocarbons; (3) nature — restoring and permanently protecting Earth's ecosystems to store and accumulate carbon and restore biodiversity; (4) food — switching to mostly plant-based diets, reducing food waste, and improving cropping practices; (5) economy — moving from indefinite GDP growth and overconsumption by the wealthy to ecological economics and a circular economy, in which prices reflect the full environmental costs of goods and services; and (6) human population
— stabilizing and gradually reducing the population by providing
voluntary family planning and supporting education and rights for all
girls and young women, which has been proven to lower fertility rates.
At the 30th anniversary of the World Scientists' Warning to Humanity,
a second update to the climate emergency declaration concluded that "We
are now at 'code red' on planet Earth".
2022 warning on population
In October 2022, Eileen Crist, William J. Ripple, Paul R. Ehrlich, William E. Rees, and Christopher Wolf all contributed to the Scientists' warning on population, published by Science of the Total Environment
as "part of the ongoing series of scientists' warning publications," to
address the negative impacts of population size and growth on the
climate and biodiversity, which they posit "continues to be ignored, sidestepped, or denied." It calls for two actions that, if heeded, will stop population growth
before the end of this century. Firstly, the authors issue a global
appeal to all adults to have no more than one child as part of the
transformative changes needed to mitigate both climate change and biodiversity loss.
Secondly, the warning urges policy-makers to "implement population
policies with two key female empowerment components," primarily
improving education for young women and girls and providing high-quality
family-planning services to all. It emphasizes that "the combination of
institutional support to plan one's child-bearing choices and
educational attainment, including enhanced opportunity for higher
education for women, yields immediate fertility declines." It also
posits that a sustainable human population,
which according to environmental analysts is "one enjoying a modest,
equitable middle-class standard of living on a planet retaining its
biodiversity and with climate-related adversities minimized," is between
2 and 4 billion people.
The warning also advocates for combatting poverty, patriarchy and overconsumption
by the affluent, and calls for a global wealth tax to be levied
primarily against "wealthy nations, industries and people who have
benefitted the most from humanity's massive-scale historical and
contemporary use of fossil fuels" in order to expand "clean sanitation
and water availability, food sovereignty, and electrification via
renewables." It stresses that poverty alleviation must include the
provision of basic public services, in particular healthcare and
education.
https://en.wikipedia.org/wiki/Global_catastrophic_risk A global catastrophic risk or a doomsday scenario is a hypothetical event that could damage human well-being on a global scale, even endangering or destroying modern civilization. An event that could cause human extinction or permanently and drastically curtail humanity's existence or potential is known as an "existential risk".
In the 21st century, a number of academic and non-profit
organizations have been established to research global catastrophic and
existential risks, formulate potential mitigation measures and either
advocate for or implement these measures.
Definition and classification
Scope–severity grid from Bostrom's paper "Existential Risk Prevention as Global Priority"
Defining global catastrophic risks
The
term global catastrophic risk "lacks a sharp definition", and generally
refers (loosely) to a risk that could inflict "serious damage to human
well-being on a global scale".
Humanity has suffered large catastrophes before. Some of these have caused serious damage but were only local in scope—e.g. the Black Death may have resulted in the deaths of a third of Europe's population, 10% of the global population at the time. Some were global, but were not as severe—e.g. the 1918 influenza pandemic killed an estimated 3–6% of the world's population.
Most global catastrophic risks would not be so intense as to kill the
majority of life on earth, but even if one did, the ecosystem and
humanity would eventually recover (in contrast to existential risks).
Similarly, in Catastrophe: Risk and Response, Richard Posner
singles out and groups together events that bring about "utter
overthrow or ruin" on a global, rather than a "local or regional" scale.
Posner highlights such events as worthy of special attention on cost–benefit grounds because they could directly or indirectly jeopardize the survival of the human race as a whole.
Defining existential risks
Existential risks are defined as "risks that threaten the destruction of humanity's long-term potential." The instantiation of an existential risk (an existential catastrophe) would either cause outright human extinction or irreversibly lock in a drastically inferior state of affairs. Existential risks are a sub-class of global catastrophic risks, where the damage is not only global but also terminal and permanent, preventing recovery and thereby affecting both current and all future generations.
Non-extinction risks
While
extinction is the most obvious way in which humanity's long-term
potential could be destroyed, there are others, including unrecoverablecollapse and unrecoverabledystopia.
A disaster severe enough to cause the permanent, irreversible collapse
of human civilisation would constitute an existential catastrophe, even
if it fell short of extinction.
Similarly, if humanity fell under a totalitarian regime, and there were
no chance of recovery then such a dystopia would also be an existential
catastrophe. Bryan Caplan writes that "perhaps an eternity of totalitarianism would be worse than extinction". (George Orwell's novel Nineteen Eighty-Four suggests an example.)
A dystopian scenario shares the key features of extinction and
unrecoverable collapse of civilization: before the catastrophe humanity
faced a vast range of bright futures to choose from; after the
catastrophe, humanity is locked forever in a terrible state.
Arrangement
of global catastrophic risks into three sets according to whether they
are largely human-caused, human influences upon nature, or purely
natural
Research
into the nature and mitigation of global catastrophic risks and
existential risks is subject to a unique set of challenges and, as a
result, is not easily subjected to the usual standards of scientific
rigour. For instance, it is neither feasible nor ethical to study these risks experimentally. Carl Sagan
expressed this with regards to nuclear war: "Understanding the
long-term consequences of nuclear war is not a problem amenable to
experimental verification".
Moreover, many catastrophic risks change rapidly as technology advances
and background conditions, such as geopolitical conditions, change.
Another challenge is the general difficulty of accurately predicting the
future over long timescales, especially for anthropogenic risks which
depend on complex human political, economic and social systems. In addition to known and tangible risks, unforeseeable black swan extinction events may occur, presenting an additional methodological problem.
Lack of historical precedent
Humanity has never suffered an existential catastrophe and if one were to occur, it would necessarily be unprecedented. Therefore, existential risks pose unique challenges to prediction, even more than other long-term events, because of observation selection effects. Unlike with most events, the failure of a complete extinction event
to occur in the past is not evidence against their likelihood in the
future, because every world that has experienced such an extinction
event has no observers, so regardless of their frequency, no
civilization observes existential risks in its history. These anthropic
issues may partly be avoided by looking at evidence that does not have
such selection effects, such as asteroid impact craters on the Moon, or
directly evaluating the likely impact of new technology.
To understand the dynamics of an unprecedented, unrecoverable
global civilizational collapse (a type of existential risk), it may be
instructive to study the various local civilizational collapses that have occurred throughout human history. For instance, civilizations such as the Roman Empire
have ended in a loss of centralized governance and a major
civilization-wide loss of infrastructure and advanced technology.
However, these examples demonstrate that societies appear to be fairly
resilient to catastrophe; for example, Medieval Europe survived the Black Death without suffering anything resembling a civilization collapse despite losing 25 to 50 percent of its population.
Incentives and coordination
There are economic reasons that can explain why so little effort is going into existential risk reduction. It is a global public good, so we should expect it to be undersupplied by markets.
Even if a large nation invests in risk mitigation measures, that nation
will enjoy only a small fraction of the benefit of doing so.
Furthermore, existential risk reduction is an intergenerational
global public good, since most of the benefits of existential risk
reduction would be enjoyed by future generations, and though these
future people would in theory perhaps be willing to pay substantial sums
for existential risk reduction, no mechanism for such a transaction
exists.
Scope insensitivity influences how bad people consider the
extinction of the human race to be. For example, when people are
motivated to donate money to altruistic causes, the quantity they are
willing to give does not increase linearly with the magnitude of the
issue: people are roughly as willing to prevent the deaths of 200,000 or
2,000 birds. Similarly, people are often more concerned about threats to individuals than to larger groups.
Substantially larger numbers, such as 500 million deaths,
and especially qualitatively different scenarios such as the extinction
of the entire human species, seem to trigger a different mode of
thinking... People who would never dream of hurting a child hear of
existential risk, and say, "Well, maybe the human species doesn't really
deserve to survive".
All past predictions of human extinction have proven to be false. To some, this makes future warnings seem less credible. Nick Bostrom
argues that the absence of human extinction in the past is weak
evidence that there will be no human extinction in the future, due to survivor bias and other anthropic effects.
SociobiologistE. O. Wilson
argued that: "The reason for this myopic fog, evolutionary biologists
contend, is that it was actually advantageous during all but the last
few millennia of the two million years of existence of the genus
Homo... A premium was placed on close attention to the near future and
early reproduction, and little else. Disasters of a magnitude that occur
only once every few centuries were forgotten or transmuted into myth."
Proposed mitigation
Multi-layer defense
Defense in depth is a useful framework for categorizing risk mitigation measures into three layers of defense:
Prevention: Reducing the probability of a catastrophe
occurring in the first place. Example: Measures to prevent outbreaks of
new highly infectious diseases.
Response: Preventing the scaling of a catastrophe to the
global level. Example: Measures to prevent escalation of a small-scale
nuclear exchange into an all-out nuclear war.
Resilience: Increasing humanity's resilience (against
extinction) when faced with global catastrophes. Example: Measures to
increase food security during a nuclear winter.
Human extinction is most likely when all three defenses are weak,
that is, "by risks we are unlikely to prevent, unlikely to successfully
respond to, and unlikely to be resilient against".
The unprecedented nature of existential risks poses a special
challenge in designing risk mitigation measures since humanity will not
be able to learn from a track record of previous events.
Funding
Some
researchers argue that both research and other initiatives relating to
existential risk are underfunded. Nick Bostrom states that more research
has been done on Star Trek, snowboarding, or dung beetles than on existential risks. Bostrom's comparisons have been criticized as "high-handed". As of 2020, the Biological Weapons Convention organization had an annual budget of US$1.4 million.
Survival planning
Some
scholars propose the establishment on Earth of one or more
self-sufficient, remote, permanently occupied settlements specifically
created for the purpose of surviving a global disaster.Economist Robin Hanson
argues that a refuge permanently housing as few as 100 people would
significantly improve the chances of human survival during a range of
global catastrophes.
Food storage
has been proposed globally, but the monetary cost would be high.
Furthermore, it would likely contribute to the current millions of
deaths per year due to malnutrition. In 2022, a team led by David Denkenberger modeled the cost-effectiveness of resilient foods to artificial general intelligence (AGI) safety and found "~98-99% confidence" for a higher marginal impact of work on resilient foods. Some survivalists stock survival retreats with multiple-year food supplies.
The Svalbard Global Seed Vault is buried 400 feet (120 m) inside a mountain on an island in the Arctic.
It is designed to hold 2.5 billion seeds from more than 100 countries
as a precaution to preserve the world's crops. The surrounding rock is
−6 °C (21 °F) (as of 2015) but the vault is kept at −18 °C (0 °F) by
refrigerators powered by locally sourced coal.
More speculatively, if society continues to function and if the biosphere
remains habitable, calorie needs for the present human population might
in theory be met during an extended absence of sunlight, given
sufficient advance planning. Conjectured solutions include growing
mushrooms on the dead plant biomass left in the wake of the catastrophe,
converting cellulose to sugar, or feeding natural gas to
methane-digesting bacteria.
Global catastrophic risks and global governance
Insufficient global governance
creates risks in the social and political domain, but the governance
mechanisms develop more slowly than technological and social change.
There are concerns from governments, the private sector, as well as the
general public about the lack of governance mechanisms to efficiently
deal with risks, negotiate and adjudicate between diverse and
conflicting interests. This is further underlined by an understanding of
the interconnectedness of global systemic risks.
In absence or anticipation of global governance, national governments
can act individually to better understand, mitigate and prepare for
global catastrophes.
Climate emergency plans
In 2018, the Club of Rome
called for greater climate change action and published its Climate
Emergency Plan, which proposes ten action points to limit global average
temperature increase to 1.5 degrees Celsius. Further, in 2019, the Club published the more comprehensive Planetary Emergency Plan.
There is evidence to suggest that collectively engaging with the
emotional experiences that emerge during contemplating the vulnerability
of the human species within the context of climate change allows for
these experiences to be adaptive. When collective engaging with and
processing emotional experiences is supportive, this can lead to growth
in resilience, psychological flexibility, tolerance of emotional
experiences, and community engagement.
Space colonization is a proposed alternative to improve the odds of surviving an extinction scenario. Solutions of this scope may require megascale engineering.
Astrophysicist Stephen Hawking advocated colonizing other planets within the Solar System once technology progresses sufficiently, in order to improve the chance of human survival from planet-wide events such as global thermonuclear war.
Billionaire Elon Musk writes that humanity must become a multiplanetary species in order to avoid extinction. Musk is using his company SpaceX to develop technology he hopes will be used in the colonization of Mars.
In a few billion years, the Sun will expand into a red giant,
swallowing the Earth. This can be avoided by moving the Earth farther
out from the Sun, keeping the temperature roughly constant. That can be
accomplished by tweaking the orbits of comets and asteroids so they pass
close to the Earth in such a way that they add energy to the Earth's
orbit. Since the Sun's expansion is slow, roughly one such encounter every 6,000 years would suffice.
Skeptics and opponents
Psychologist Steven Pinker has called existential risk a "useless category" that can distract from real threats such as climate change and nuclear war.
Organizations
The Bulletin of the Atomic Scientists
(est. 1945) is one of the oldest global risk organizations, founded
after the public became alarmed by the potential of atomic warfare in
the aftermath of WWII. It studies risks associated with nuclear war and
energy and famously maintains the Doomsday Clock established in 1947. The Foresight Institute
(est. 1986) examines the risks of nanotechnology and its benefits. It
was one of the earliest organizations to study the unintended
consequences of otherwise harmless technology gone haywire at a global
scale. It was founded by K. Eric Drexler who postulated "grey goo".
Beginning after 2000, a growing number of scientists,
philosophers and tech billionaires created organizations devoted to
studying global risks both inside and outside of academia.
Independent non-governmental organizations (NGOs) include the Machine Intelligence Research Institute (est. 2000), which aims to reduce the risk of a catastrophe caused by artificial intelligence, with donors including Peter Thiel and Jed McCaleb. The Nuclear Threat Initiative
(est. 2001) seeks to reduce global threats from nuclear, biological and
chemical threats, and containment of damage after an event. It maintains a nuclear material security index. The Lifeboat Foundation (est. 2009) funds research into preventing a technological catastrophe. Most of the research money funds projects at universities. The Global Catastrophic Risk Institute (est. 2011) is a US-based non-profit, non-partisan think tank founded by Seth Baum
and Tony Barrett. GCRI does research and policy work across various
risks, including artificial intelligence, nuclear war, climate change,
and asteroid impacts. The Global Challenges Foundation (est. 2012), based in Stockholm and founded by Laszlo Szombatfalvy, releases a yearly report on the state of global risks. The Future of Life Institute
(est. 2014) works to reduce extreme, large-scale risks from
transformative technologies, as well as steer the development and use of
these technologies to benefit all life, through grantmaking, policy
advocacy in the United States, European Union and United Nations, and
educational outreach. Elon Musk, Vitalik Buterin and Jaan Tallinn are some of its biggest donors.
The Center on Long-Term Risk (est. 2016), formerly known as the
Foundational Research Institute, is a British organization focused on
reducing risks of astronomical suffering (s-risks) from emerging technologies.
University-based organizations included the Future of Humanity Institute (est. 2005) which researched the questions of humanity's long-term future, particularly existential risk. It was founded by Nick Bostrom and was based at Oxford University. The Centre for the Study of Existential Risk
(est. 2012) is a Cambridge University-based organization which studies
four major technological risks: artificial intelligence, biotechnology,
global warming and warfare. All are man-made risks, as Huw Price
explained to the AFP news agency, "It seems a reasonable prediction
that some time in this or the next century intelligence will escape from
the constraints of biology". He added that when this happens "we're no
longer the smartest things around," and will risk being at the mercy of
"machines that are not malicious, but machines whose interests don't
include us." Stephen Hawking was an acting adviser. The Millennium Alliance for Humanity and the Biosphere
is a Stanford University-based organization focusing on many issues
related to global catastrophe by bringing together members of academia
in the humanities. It was founded by Paul Ehrlich, among others. Stanford University also has the Center for International Security and Cooperation focusing on political cooperation to reduce global catastrophic risk. The Center for Security and Emerging Technology
was established in January 2019 at Georgetown's Walsh School of Foreign
Service and will focus on policy research of emerging technologies with
an initial emphasis on artificial intelligence. They received a grant of 55M USD from Good Ventures as suggested by Open Philanthropy.
Other risk assessment groups are based in or are part of governmental organizations. The World Health Organization (WHO) includes a division called the Global Alert and Response (GAR) which monitors and responds to global epidemic crisis. GAR helps member states with training and coordination of response to epidemics. The United States Agency for International Development (USAID) has its Emerging Pandemic Threats Program which aims to prevent and contain naturally generated pandemics at their source. The Lawrence Livermore National Laboratory
has a division called the Global Security Principal Directorate which
researches on behalf of the government issues such as bio-security and
counter-terrorism.
Global average temperatures show that the Little Ice Age was not a
distinct planet-wide period but a regional phenomenon occurring near the
end of a long temperature decline that preceded recent global warming.
The Little Ice Age (LIA) was a period of regional cooling, particularly pronounced in the North Atlantic region. It was not a true ice age of global extent. The term was introduced into scientific literature by François E. Matthes in 1939. The period has been conventionally defined as extending from the 16th to the 19th centuries, but some experts prefer an alternative time-span from about 1300 to about 1850.
The NASA Earth Observatory
notes three particularly cold intervals. One began about 1650, another
about 1770, and the last in 1850, all of which were separated by
intervals of slight warming. The Intergovernmental Panel on Climate ChangeThird Assessment Report
considered that the timing and the areas affected by the LIA suggested
largely independent regional climate changes, rather than a globally
synchronous increased glaciation. At most, there was modest cooling of
the Northern Hemisphere during the period.
Evidence from mountain glaciers
does suggest increased glaciation in a number of widely spread regions
outside Europe prior to the twentieth century, including Alaska, New
Zealand and Patagonia.
However, the timing of maximum glacial advances in these regions
differs considerably, suggesting that they may represent largely
independent regional climate changes,
not a globally-synchronous increased glaciation. Thus current evidence
does not support globally synchronous periods of anomalous cold or
warmth over this interval, and the conventional terms of "Little Ice
Age" and "Medieval Warm Period"
appear to have limited utility in describing trends in hemispheric or
global mean temperature changes in past centuries.... [Viewed]
hemispherically, the "Little Ice Age" can only be considered as a modest
cooling of the Northern Hemisphere during this period of less than 1°C
relative to late twentieth century levels.
The IPCC Fourth Assessment Report (AR4) of 2007 discusses more recent research and gives particular attention to the Medieval Warm Period:
...when viewed together, the currently available
reconstructions indicate generally greater variability in centennial
time scale trends over the last 1 kyr
than was apparent in the TAR.... The result is a picture of relatively
cool conditions in the seventeenth and early nineteenth centuries and
warmth in the eleventh and early fifteenth centuries, but the warmest
conditions are apparent in the twentieth century. Given that the
confidence levels surrounding all of the reconstructions are wide,
virtually all reconstructions are effectively encompassed within the
uncertainty previously indicated in the TAR. The major differences
between the various proxy reconstructions relate to the magnitude of
past cool excursions, principally during the twelfth to fourteenth,
seventeenth and nineteenth centuries.
Dating
The last written records of the Norse Greenlanders are from a 1408 marriage at Hvalsey Church, which is now the best-preserved Norse ruin.
There is no consensus on when the Little Ice Age began, but a series of events before the known climatic minima have often been referenced. In the 13th century, pack ice began advancing southwards in the North Atlantic, as did glaciers in Greenland.
Anecdotal evidence suggests expanding glaciers almost worldwide. Based
on radiocarbon dating of roughly 150 samples of dead plant material with
roots intact that were collected from beneath ice caps on Baffin Island and Iceland, Miller et al. (2012)
state that cold summers and ice growth began abruptly between 1275 and
1300, followed by "a substantial intensification" from 1430 to 1455.
In contrast, a climate reconstruction based on glacial length shows no great variation from 1600 to 1850 but a strong retreat thereafter.
Therefore, any of several dates ranging over 400 years may indicate the beginning of the Little Ice Age:
1560 to 1630 for when the worldwide glacial expansion, known as the Grindelwald Fluctuation, began
1650, not the start of the Little Ice Age, but the start of the coldest years midway through, i.e., the First Climatic Minimum
The Little Ice Age ended in the latter half of the 19th century or in the early 20th century.
The 6th report of the IPCC describes the coldest period in the last millennium as:
"...a multi-centennial period of relatively low temperature beginning around the 15th century, with GMST averaging –0.03 [–0.30 to 0.06] °C between 1450 and 1850 relative to 1850–1900."
By region
Europe
The Frozen Thames, 1677
Drangajökull, Iceland's northernmost glacier, reached its maximum extent during the LIA around 1400 CE.
The Baltic Sea
froze over twice, in 1303 and 1306–1307, and years followed of
"unseasonable cold, storms and rains, and a rise in the level of the
Caspian Sea." The Little Ice Age brought colder winters to parts of Europe and North America. Farms and villages in the Swiss Alps were destroyed by encroaching glaciers during the mid-17th century.
Canals and rivers in Great Britain and the Netherlands were frequently
frozen deeply enough to support ice skating and winter festivals.
As trade needed to continue during the prolonged winter often spanning 5
months, merchants equipped their boer style boats with planks and
skates (runners), hence the iceboat was born. The first River Thames frost fair was in 1608 and the last in 1814. Changes to the bridges and the addition of the Thames Embankment have affected the river's flow and depth and greatly diminish the possibility of further freezes.
The winter of 1794–1795 was particularly harsh: the French invasion army under Pichegru marched on the frozen rivers of the Netherlands, and the Dutch fleet was locked in the ice in Den Helder harbour.
Sea ice surrounding Iceland
extended for miles in every direction and closed harbors to shipping.
The population of Iceland fell by half, but that may have been caused by
skeletal fluorosis after the eruption of Laki in 1783. Iceland also suffered failures of cereal crops and people moved away from a grain-based diet.
After Greenland's
climate became colder and stormier around 1250, the diet of the Norse
Viking settlements there steadily shifted away from agricultural
sources. By around 1300, seal
hunting provided over three quarters of their food. By 1350, there was
reduced demand for their exports, and trade with Europe fell away. The
last document from the settlements dates from 1412, and over the
following decades, the remaining Europeans left in what seems to have
been a gradual withdrawal, which was caused mainly by economic factors
such as increased availability of farms in Scandinavian countries. Greenland was largely cut off by ice from 1410 to the 1720s.
Between 1620 and 1740, the Yzeron Basin in the Massif Central
of France witnessed a phase of decreased fluvial activity. This decline
in fluvial activity is believed to be linked to a multidecennial phase
of droughts in the western Mediterranean.
In Southwestern Europe, a negative North Atlantic oscillation (NAO) combined with increased aridity caused an increase in wind-driven sediment deposition during the LIA.
Winter skating on the main canal of Pompenburg, Rotterdam in 1825, shortly before the minimum, by Bartholomeus Johannes van Hove
In his 1995 book, the early climatologist Hubert Lamb
said that in many years, "snowfall was much heavier than recorded
before or since, and the snow lay on the ground for many months longer
than it does today." In Lisbon, Portugal, snowstorms were much more frequent than today, and one winter in the 17th century produced eight snowstorms.
Many springs and summers were cold and wet but with great variability
between years and groups of years. That was particularly evident during
the "Grindelwald Fluctuation" (1560–1630); the rapid cooling phase was
associated with more erratic weather, including increased storminess,
unseasonal snowstorms, and droughts.
Crop practices throughout Europe had to be altered to adapt to the
shortened and less reliable growing season, and there were many years of
scarcity and famine. One was the Great Famine of 1315–1317, but that may have been before the Little Ice Age.
According to Elizabeth Ewan and Janay Nugent, "Famines in France
1693–94, Norway 1695–96 and Sweden 1696–97 claimed roughly 10 percent of
the population of each country. In Estonia and Finland in 1696–97,
losses have been estimated at a fifth and a third of the national
populations, respectively." Viticulture disappeared from some northern regions, and storms caused serious flooding and loss of life. Some of them resulted in the permanent loss of large areas of land from the Danish, German, and Dutch coasts.
The violinmaker Antonio Stradivari produced his instruments during the Little Ice Age. The colder climate may have caused the wood that was used in his violins to be denser than in warmer periods and to contribute to the tone of his instruments. According to the science historian James Burke,
the period inspired such novelties in everyday life as the widespread
use of buttons and button-holes, as well as knitting of custom-made
undergarments for the better covering and insulating of the body.
Chimneys were invented to replace open fires in the centre of communal
halls to allow houses with multiple rooms to have the separation of
masters from servants.
The Little Ice Age, by the anthropologist Brian Fagan of the University of California at Santa Barbara, describes the plight of European peasants from 1300 to 1850: famines, hypothermia, bread riots
and the rise of despotic leaders brutalizing an increasingly dispirited
peasantry. In the late 17th century, agriculture had dropped off
dramatically: "Alpine villagers lived on bread made from ground
nutshells mixed with barley and oat flour." Historian Wolfgang Behringer has linked intensive witch-hunting episodes in Europe to agricultural failures during the Little Ice Age.
David Vinckboons, Winter Landscape with Skaters and Ice-Sailing (ca. 1615)
The Frigid Golden Age, by the environmental historian Dagomar Degroot of Georgetown University,
points out that some societies thrived, but others faltered during the
Little Ice Age. In particular, the Little Ice Age transformed
environments around the Dutch Republic
and made them easier to exploit in commerce and conflict. The Dutch
were resilient, even adaptive, in the face of weather that devastated
neighboring countries. Merchants exploited harvest failures, military
commanders took advantage of shifting wind patterns, and inventors
developed technologies that helped them profit from the cold. The
17th-century Dutch Golden Age therefore owed much to its people's flexibility in coping with the changing climate.
Cultural responses
Historians have argued that cultural responses to the consequences of the Little Ice Age in Europe consisted of violent scapegoating. The prolonged cold, dry periods brought drought upon many European
communities and resulted in poor crop growth, poor livestock survival,
and increased activity of pathogens and disease vectors.
Disease intensified under the same conditions that unemployment and
economic difficulties arose: prolonged cold, dry seasons. Disease and
unemployment generated a lethal positive feedback loop.
Although the communities had some contingency plans, such as better
crop mixes, emergency grain stocks, and international food trade, they
did not always prove effective.
Communities often lashed out via violent crimes, including robbery and
murder. Accusations of sexual offenses also increased, such as adultery, bestiality, and rape.
Europeans sought explanations for the famine, disease, and social
unrest that they were experiencing, and they blamed the innocent.
Evidence from several studies indicate that increases in violent actions
against marginalized groups, which were held responsible for the Little
Ice Age, overlap with the years of particularly cold, dry weather.
One example of the violent scapegoating occurring during the Little Ice Age was the resurgence of witchcraft trials.
Oster (2004) and Behringer (1999) argue that the resurgence was brought
by the climatic decline. Prior to the Little Ice Age, witchcraft was
considered an insignificant crime, and victims (the supposed witches)
were rarely accused. But beginning in the 1380s, just as the Little Ice Age began, European populations began to link magic and weather-making.
The first systematic witch hunts began in the 1430s, and by the 1480s,
it was widely believed that witches should be held accountable for poor
weather.
Witches were blamed for direct and indirect consequences of the Little
Ice Age: livestock epidemics, cows that gave too little milk, late
frosts, and unknown diseases. In general, the number of witchcraft trials rose as the temperature dropped, and trials decreased when temperature increased.
The peaks of witchcraft persecutions overlap with the hunger crises
that occurred in 1570 and 1580, the latter lasting a decade.
The trials targeted primarily poor women, many of them widows. Not
everybody agreed that witches should be persecuted for weather-making,
but such arguments focused primarily not upon whether witches existed
but upon whether witches had the capability to control the weather. The Catholic Church in the Early Middle Ages
argued that witches could not control the weather because they were
mortals, not God, but by the mid-13th century, most people agreed with
the idea that witches could control natural forces.
Jewish populations were also blamed for climatic deterioration during the Little Ice Age. The Western European states experienced waves of anti-Semitism, directed against the main religious minority in their otherwise Christian societies. There was no direct link made between Jews and the weather; they were blamed only for indirect consequences such as disease. Outbreaks of the Black Death were often blamed on Jews. In Western European cities during the 1300s, Jewish populations were murdered to stop the spread of the plague. Rumors spread that Jews were either poisoning wells themselves, or telling lepers to poison the wells. To escape persecution, some Jews converted to Christianity, while others migrated to the Ottoman Empire, Italy or the Holy Roman Empire, where they experienced greater toleration.
Some populations blamed the cold periods and the resulting famine
and disease during the Little Ice Age on a general divine displeasure. Particular groups took the brunt of the burden in attempts to cure it. In Germany, regulations were imposed upon activities such as gambling and drinking, which disproportionately affected the lower class and women were forbidden from showing their knees.
Other regulations affected the wider population, such as prohibiting
dancing, sexual activities and moderating food and drink intake. In Ireland, Catholics blamed the Reformation for the bad weather. The Annals of Loch Cé,
in its entry for 1588, describes a midsummer snowstorm as "a wild apple
was not larger than each stone of it" and blames it on the presence of a
"wicked, heretical, bishop in Oilfinn", the ProtestantBishop of Elphin, John Lynch.
William James Burroughs analyzes the depiction of winter in paintings, as does Hans Neuberger.
Burroughs asserts that it occurred almost entirely from 1565 to 1665
and was associated with the climatic decline from 1550 onwards.
Burroughs claims that there had been almost no depictions of winter in
art, and he "hypothesizes that the unusually harsh winter of 1565
inspired great artists to depict highly original images and that the
decline in such paintings was a combination of the 'theme' having been
fully explored and mild winters interrupting the flow of painting."
Wintry scenes, which entail technical difficulties in painting, have
been regularly and well handled since at least the early 15th century by
artists in illuminated manuscript cycles that show the Labours of the Months, typically placed on the calendar pages of books of hours. January and February are typically shown as snowy, as in February in the famous cycle in the Très Riches Heures du Duc de Berry, painted in 1412–1416 and illustrated below. Since landscape painting
had not yet developed as an independent genre in art, the absence of
other winter scenes is not remarkable. On the other hand, snowy winter
landscapes, particularly stormy seascapes, became artistic genres in the
Dutch Golden Age painting during the coldest and stormiest decades of the Little Ice Age.
Most modern scholars believe them to be full of symbolic messages and
metaphors, which would have been clear to contemporary viewers.
All of the famous winter landscape paintings by Pieter Bruegel the Elder, such as The Hunters in the Snow and the Massacre of the Innocents, are thought to have been painted around 1565. His son Pieter Brueghel the Younger
(1564–1638) also painted many snowy landscapes, but according to
Burroughs, he "slavishly copied his father's designs. The derivative
nature of so much of this work makes it difficult to draw any definite
conclusions about the influence of the winters between 1570 and
1600...". In addition, Breugel painted Hunters in the Snow in Antwerp, so the mountains in the picture probably mean it was based on drawings or memories from crossing of the Alps
during his trip to Rome in 1551–1552. It is one of 5 known surviving
paintings, probably from a series of 6 or 12, known as “the Twelve
Months”, that Breugel was commissioned to paint by a wealthy patron in Antwerp, Nicolaes Jonghelinck (Hunters in the Snow being for January): none of the other four that survive show a snow-covered landscape and both The Hay Harvest (July) and The Harvesters (August) depict warm summer days. Even The Return of the Herd (thought to be the painting for November) and The Gloomy Day (known to be for February) show landscapes free of snow.
Burroughs says that snowy subjects return to Dutch Golden Age painting with works by Hendrick Avercamp
from 1609 onwards. There is a hiatus between 1627 and 1640, which is
before the main period of such subjects from the 1640s to the 1660s.
That relates well with climate records for the later period. The
subjects are less popular after about 1660, but that does not match any
recorded reduction in severity of winters and may reflect only changes
in taste or fashion. In the later period between the 1780s and 1810s,
snowy subjects again became popular.
Neuberger analyzed 12,000 paintings, held in American and European
museums and dated between 1400 and 1967, for cloudiness and darkness. His 1970 publication shows an increase in such depictions that corresponds to the Little Ice Age, which peaks between 1600 and 1649.
Paintings and contemporary records in Scotland demonstrate that curling, ice skating and icesailing
were popular outdoor winter sports, with curling dating to the 16th
century and becoming widely popular in the mid-19th century. An outdoor curling pond constructed in Gourock
in the 1860s remained in use for almost a century, but increasing use
of indoor facilities, problems of vandalism, and milder winters led to
the pond being abandoned in 1963.
General Crisis of the seventeenth century
The General Crisis
of the seventeenth century in Europe was a period of inclement weather,
crop failure, economic hardship, extreme intergroup violence, and high
mortality linked to the Little Ice Age. Episodes of social instability
track the cooling with a time lapse of up to 15 years, and many
developed into armed conflicts, such as the Thirty Years' War (1618–1648). The war started as a war of succession to the Bohemian throne. Animosity between Protestants
and Catholics in the Holy Roman Empire (now Germany) added fuel to the
fire. It soon escalated to a huge conflict that involved all the major
European powers and devastated much of Germany. When the war ended, some
regions of the Holy Roman Empire had seen their population drop by as
much as 70%.
Early European explorers and settlers of North America reported
exceptionally severe winters. In southwestern Alaska, preexisting
flexibility in foraging habits among the native people lent itself to
high adaptability to the LIA. Both Europeans and indigenous peoples suffered excess mortality in Maine during the winter of 1607–1608, and extreme frost was meanwhile reported in the Jamestown, Virginia, settlement. Native Americans formed leagues in response to food shortages. The journal of Pierre de Troyes, Chevalier de Troyes, who led an expedition to James Bay
in 1686, recorded that the bay was still littered with so much floating
ice that he could hide behind it in his canoe on 1 July. In the winter of 1780, New York Harbor froze, which allowed people to walk from Manhattan Island to Staten Island.
The extent of mountain glaciers had been mapped by the late 19th
century. In the north and the south temperate zones, Equilibrium Line
Altitude (the boundaries separating zones of net accumulation from those
of net ablation) were about 100 metres (330 ft) lower than they were in
1975. Southwestern Alaska experienced a tamperature nadir around 135 BP, and in south-central Alaska, mountain hemlock forests severely declined. In Glacier National Park, the last episode of glacier advance came in the late 18th and the early 19th centuries. In 1879, the famed naturalist John Muir found that Glacier Bay ice had retreated 48 miles (77 km). In Chesapeake Bay, Maryland, large temperature excursions were possibly related to changes in the strength of the North Atlantic thermohaline circulation.
Because the Little Ice Age took place during the European colonization of the Americas,
it discouraged many early colonists, who had expected the climate of
North America to be similar to the climate of Europe at similar
latitudes. They found that North America, at least in what would become
Canada and the northern United States, had hotter summers and colder
winters than Europe. That effect was aggravated by the Little Ice Age,
and unpreparedness led to the collapse of many early European
settlements in North America.
Historians agree that when colonists settled at Jamestown,
it was one of the coldest periods in the last 1000 years. Drought was
also a problem in North America during the Little Ice Age, and the
settlers arrived in Roanoke during the largest drought of the past 800
years. Tree ring studies by the University of Arkansas discovered that
many colonists arrived at the beginning of a seven-year drought. The
droughts also decreased the Native American populations and led to
conflict because of food scarcity. English colonists at Roanoke forced
Native Americans of Ossomocomuck to share their depleted supplies with
them. That led to warfare between the two groups, and Native American
towns were destroyed. That cycle would repeat itself many times at
Jamestown. The combination of fighting and cold weather also led to the
spread of diseases. The colder weather helped the parasites brought by
Europeans in mosquitoes to develop faster. That in turn led to many
malaria deaths among Native Americans.
In 1642, Thomas Gorges wrote that between 1637 and 1645,
colonists in Maine (then part of Massachusetts) experienced horrendous
weather conditions. In June 1637, temperatures were so high that
numerous European settlers died; travelers were forced to travel at
night to stay cool. Gorges also wrote that the winter of 1641–1642 was
“piercingly Intolerable” and that no Englishman or Native American had
ever seen anything like it. He also stated that the Massachusetts Bay
had frozen as far as one could see, and that horse carriages now roamed
where ships used to be. He stated that the summers of 1638 and 1639 were
very short, cold, and wet, which compounded food scarcity for a few
years. To make matters worse, creatures like caterpillars and pigeons
fed on crops and devastated harvests. Every year about which Gorges
wrote featured unusual weather patterns, including high precipitation,
drought, and extreme cold or heat.
Many inhabitants of North America had their own theories about the extreme weather. The colonist Ferdinando Gorges blamed the cold weather on cold ocean winds. Humphrey Gilbert
tried to explain Newfoundland's icy and foggy weather by saying that
the Earth drew cold vapors from the ocean and drew them west. Many
others had their own theories for North America being so much colder
than Europe; their observations and hypotheses offer insight on the
Little Ice Age's effects in North America.
Mesoamerica
An analysis of several climate proxies undertaken in Mexico's Yucatán Peninsula, which was linked by its authors to Maya and Aztec chronicles relating periods of cold and drought, supports the existence of the Little Ice Age in the region.
Another study conducted in several sites in Mesoamerica like Los
Tuxtlas and Lake Pompal in Veracruz, Mexico show a decrease in human
activity in the area during the Little Ice Age. That was proven by
studying charcoal fragments and the amount of maize pollen taken from
sedimentary samples by using a nonrotatory piston corer. The samples
also showed volcanic activity which caused forest regeneration between
650 and 800. The instances of volcanic activity near Lake Pompal
indicate varying temperatures, not a continuous coldness, during the
Little Ice Age in Mesoamerica.
Atlantic Ocean
In the North Atlantic, sediments accumulated since the end of the last ice age,
which occurred nearly 12,000 years ago, show regular increases in the
amount of coarse sediment grains deposited from icebergs melting in the
now-open ocean, indicating a series of 1–2 °C (2–4 °F) cooling events
that recur every 1,500 years or so.
The most recent cooling event was the Little Ice Age. The same cooling
events are detected in sediments accumulating off Africa, but the
cooling events appear to be larger: 3–8 °C (6–14 °F). δ18O values from chironomid remains in the Azores reflect the cooling of the LIA.
Although the original designation of a Little Ice Age referred to the
reduced temperature of Europe and North America, there is some evidence
of extended periods of cooling outside those regions although it is not
clear whether they are related or independent events. Mann states:
While there is evidence that many other regions outside
Europe exhibited periods of cooler conditions, expanded glaciation, and
significantly altered climate conditions, the timing and nature of these
variations are highly variable from region to region, and the notion of
the Little Ice Age as a globally synchronous cold period has all but
been dismissed.
In China, warm-weather crops such as oranges were abandoned in Jiangxi Province, where they had been grown for centuries. Also, the two periods of most frequent typhoon strikes in Guangdong coincide with two of the coldest and driest periods in northern and central China (1660–1680, 1850–1880). Scholars have argued that one of the reasons for the fall of the Ming dynasty may have been the droughts and famines that were caused by the Little Ice Age.
There are debates on the start date and the periods of Little Ice
Age's effects. Most scholars agree on categorizing the Little Ice Age
period into three distinct cold periods: in 1458–1552, 1600–1720, and
1840–1880. According to data from the U.S. National Oceanic and Atmospheric Administration, the eastern monsoon
area of China was the earliest to experience the effects of the Little
Ice Age, from 1560 to 1709. In the western region of China surrounding
the Tibetan Plateau, the effects of the Little Ice Age lagged behind the eastern region, with significant cold periods from 1620 to 1749.
As the Medieval Warm Period transitioned into the Little Ice Age, the
East Asian Summer Monsoon (EASM) became much weaker and the summer
monsoon limit (SML) migrated southeastwards.
Southwestern China became significantly colder and drier as a result of
the weakening of the EASM caused by the decreased pressure gradient
resulting from the cooling of the southern Eurasian landmass, while
northwestern China, dominated by westerlies, saw an increase in
precipitation.
The temperature changes were unprecedented for the farming communities in China. According to Coching Chu's
1972 study, the Little Ice Age from the end of the Ming dynasty to the
start of the Qing dynasty (1650–1700) was one of the coldest periods in
recorded Chinese history.
Many major droughts during the summer months were recorded, and
significant freezing events occurred during the winter months. That
greatly worsened the food supply during the Ming dynasty.
This period of Little Ice Age corresponded to the period's major historical events. The Jurchen people lived in Northern China and formed a tributary state to the Ming dynasty and its Wanli Emperor.
From 1573 to 1620, Manchuria experienced famine caused by extreme
snowfall, which depleted agriculture production and devastated the
livestock population. Scholars have argued that it had been caused by
the temperature drops during the Little Ice Age. Despite the lack of
food production, the Wanli Emperor ordered the Jurchens to pay the same
amount of tribute each year. That led to anger and sowed seeds to the
rebellion against the Ming dynasty. In 1616, Jurchens established the Later Jin dynasty. Led by Hong Taiji and Nurhaci,
the Later Jin dynasty moved South and achieved decisive victories in
battles against the Ming dynasty's military, such as during the 1618 Battle of Fushun.
After the earlier defeats and the death of the Wanli Emperor, the Chongzhen Emperor
took over China and continued the war effort. From 1632 to 1641, the
Little Ice Age began to cause drastic climate changes in the Ming
dynasty's territories. For example, rainfall in the Huabei region dropped by 11% to 47% from the historical average. Meanwhile, the Shaanbei region, along the Yellow River experienced six major floods, which ruined cities such as Yan'an.
The climate factored heavily in weakening the government's control over
China and accelerated the fall of the Ming dynasty. In 1644, Li Zicheng led the Later Jin's forces into Beijing, overthrew the Ming dynasty, and established the short-lived Shun dynasty which were soon overthrown by Qing dynasty.
During the early years of the Qing dynasty, the Little Ice Age
continued to have a significant impact on Chinese society. During the
rule of the Kangxi Emperor
(1661–1722), most Qing territories were still much colder than the
historical average. However, the Kangxi Emperor pushed reforms and
managed to increase the socio-economic recovery from the natural
disasters. He benefited partly from the peacefulness of the early Qing
dynasty. That essentially marked the end of the Little Ice Age in China
and led to a more prosperous era of Chinese history that is known as the
High Qing era.
In the Himalayas,
the general assumption is that the cooling events were synchronous with
those in Europe during the Little Ice Age because of the
characteristics of moraines. However, applications of Quaternary dating methods such as surface exposure dating
have showed that glacial maxima occurred between 1300 and 1600,
slightly earlier than the recorded coldest period in the Northern
Hemisphere. Many large Himalayan glacial debris fields have remained
close to their limits since the Little Ice Age. The Himalayas also
experienced an increase in snowfall at higher altitudes, which results
in a southward shift in the Indian summer monsoon and an increase in
precipitation. Overall, the increase in winter precipitation may have
caused some glacial movements. Since the end of the Little Ice Age, there has been an almost continuous retreat of glaciers to present.
On Rebun Island,
a rapid cooling event occurred around 390 BP amidst a longer-term trend
of cooling; this cooling event marked the onset of the Little Ice Age
in the region.
Africa
The Little Ice Age influenced the African climate from the 14th to the 19th centuries.
Despite variances throughout the continent, a general trend of
declining temperatures in Africa led to an average cooling of 1 °C.
In Ethiopia and North Africa, permanent snow was reported on mountain peaks at levels at which it does not occur today. Timbuktu, an important city on the trans-Saharan caravan route, was flooded at least 13 times by the Niger River, but there are no records of similar flooding before or since that time.
Several paleoclimatic studies of Southern Africa have suggested
significant changes in relative changes in climate and environmental
conditions. In Southern Africa, sediment cores retrieved from Lake Malawi show colder conditions between 1570 and 1820, which "further support, and extend, the global expanse of the Little Ice Age." A novel 3,000-year temperature reconstruction method, based on the rate of stalagmite
growth in a cold cave in South Africa, further suggests a cold period
from 1500 to 1800 "characterizing the South African Little Ice age."
The δ18O stalagmite record temperature reconstruction over a 350-year
period (1690–1740) suggests that South Africa may have been the coldest
region in Africa and have cooled by as much as 1.4 °C in summer.
Also, the solar magnetic and Niño-Southern Oscillation cycles may have
been key drivers of climate variability in the subtropical region. Periglacial features in the eastern Lesotho Highlands might have been reactivated by the Little Ice Age.
Another archaeological reconstruction of South Africa reveals the rise
of the Great Zimbabwe people because of ecological advantages from the
increased rainfall over other competitor societies, such as the
Mupungubwe people. Pollen records derived from rock hyrax middens in the Cederberg Mountains of southwestern South Africa indicate an increase in humidity in the region at the start of the LIA.
Other than temperature variability, data from equatorial East
Africa suggest impacts to the hydrologic cycle in the late 1700s.
Historical data reconstructions from ten major African lakes indicate
that an episode of “drought and desiccation” occurred throughout East
Africa.
The period showed drastic reductions in the depths of lakes, which were
transformed into desiccated puddles. It is very likely that locals
could cross Lake Chad, among others, and that bouts of “intense droughts
were ubiquitous.” That indicates local societies were probably launched
into long migrations and warfare with neighboring tribes, since
agriculture was made virtually useless by the dry soil.
Kreutz et al. (1997) compared results from studies of West Antarctic ice cores with the Greenland Ice Sheet Project Two GISP2; they suggested a synchronous global cooling. An ocean sediment core from the eastern Bransfield Basin in the Antarctic Peninsula shows centennial events, which the authors link to the Little Ice Age and to the Medieval Warm Period.
The authors note that "other unexplained climatic events comparable in
duration and amplitude to the LIA and MWP events also appear."
The Siple Dome
(SD) had a climate event with an onset time that is coincident with
that of the Little Ice Age in the North Atlantic, based on a correlation
with the GISP2 record. The Little Ice Age is the most dramatic climate
event in the SD Holocene glaciochemical record.
The Siple Dome ice core also contained its highest rate of melt layers
(up to 8%) between 1550 and 1700, most likely because of warm summers. Law Dome ice cores show lower levels of CO2 mixing ratios from 1550 to 1800, which Etheridge and Steele believe to be "probably as a result of colder global climate."
Sediment cores in Bransfield Basin, Antarctic Peninsula, have neoglacial indicators by diatom and sea-ice taxa variations during the Little Ice Age.
Stable isotope records from the Mount Erebus Saddle ice core site
suggests that the Ross Sea region experienced average temperatures 1.6 ±
1.4 °C cooler during the Little Ice Age than the last 150 years.
Australia and New Zealand
Its
location in the Southern Hemisphere made Australia not experience a
regional cooling like that of Europe or North America. Instead, the
Australian Little Ice Age was characterized by humid, rainy climates,
which were followed by drying and aridification in the 19th century.
As studied by Tibby et al. (2018), lake records from Victoria, New South Wales, and Queensland
suggest that conditions in the east and the south-east of Australia
were wet and unusually cool from the 16th to the early 19th centuries.
That corresponds with the “peak” of the global Little Ice Age from 1594
to 1722. For example, North Stradbroke Island's Swallow Lagoon data
reveals a period of persistent wetness from 1500 to 1850 CE (exceeding
300 mm above average), followed by a significant decrease in rainfall
after 1891. The rainfalls significantly reduced after around 1890. Similarly, the hydrological records of Lake Surprise's salinity
levels reveal high humidity levels around from 1440 to 1880, and an
increase in salinity from 1860 to 1880 points to a negative change to
the once-humid climate. The mid-19th century marked a notable change to eastern Australia's rainfall and humidity patterns.
Tibby et al. (2018) note that in eastern Australia, the
paleoclimatic changes of the Little Ice Age in the late 1800s coincided
with the agricultural changes resulting from European colonization.
After the 1788 establishment of British colonies in the Australia, which
were concentrated primarily in the eastern regions and cities like
Sydney and later Melbourne and Brisbane, the British introduced new
agricultural practices like pastoralism.
Such practices required widespread deforestation and clearance of
vegetation. Pastoralism and the clearing of land are captured in works
of art such as the 1833 painting by the prominent landscape artist John
Glover Patterdale Landscape with Cattle.
Patterdale Landscape with Cattle
(1833) by John Glover depicts agricultural practices like pastoralism,
which contributed to the aridification of Australia's late Little Ice
Age.
Over the next century, the deforestation led to a loss of biodiversity, wind and water-based soil erosion, and soil salinity.
Furthermore, as argued by Gordan et al. (2003), such land and
vegetation clearance in Australia resulted in a 10% reduction in the
transport of water vapor to the atmosphere. That occurred in Western
Australia as well, where 19th-century land clearing resulted in reduced
rainfall over the region.
By 1850 to 1890, those human agricultural practices, which were
concentrated in eastern Australia, had most likely amplified the drying
and aridification that marked the end of the Little Ice Age.
In the north, evidence suggests fairly dry conditions, but coral cores from the Great Barrier Reef
show rainfall similar to today but with less variability. A study that
analyzed isotopes in Great Barrier Reef corals suggested that increased
water vapor transport from the southern tropical oceans to the poles
contributed to the Little Ice Age. Borehole reconstructions from Australia suggest that over the last 500 years, the 17th century was the coldest on the continent.
The borehole temperature reconstruction method further indicates that
the warming of Australia over the past five centuries is only around
half that of the warming experienced by the Northern Hemisphere, which
further proves that Australia did not reach the same depths of cooling
as the continents in the north.
On the west coast of the Southern Alps of New Zealand, the Franz Josef Glacier
advanced rapidly during the Little Ice Age and reached its maximum
extent in the early 18th century. That was one of the few cases of a
glacier thrusting into a rainforest.
Evidence suggests, corroborated by tree ring proxy data, that the
glacier contributed to a −0.56 °C (−1.01 °F) temperature anomaly over
the course of the Little Ice Age in New Zealand. Based on dating of a yellow-green lichen of the Rhizocarpon subgenus, the Mueller Glacier, on the eastern flank of the Southern Alps within Aoraki / Mount Cook National Park, is considered to have been at its maximum extent between 1725 and 1730.
Pacific islands
Sea-level data for the Pacific islands
suggest that sea level in the region fell, possibly in two stages,
between 1270 and 1475. That was associated with a 1.5 °C fall in
temperature, as determined from oxygen-isotope analysis, and an observed
increase in the frequency of El Niño. Tropical Pacific coral records indicate the most frequent and intense El Niño–Southern Oscillation activity was in the mid-17th century. Foraminiferal 18 O records indicate that the Indo-Pacific Warm Pool
was warm and saline between 1000 and 1400, with temperatures
approximating current conditions, but that it cooled from 1400 onwards
and reached its lowest temperatures in 1700. That is consistent with the
transition from the mid-Holocene warming to the Little Ice Age.
The nearby southwestern Pacific, however, experienced
warmer-than-average conditions over the course of the Little Ice Age,
which is thought to be from the increased trade winds, which increased
the evaporation and the salinity in the region. The dramatic temperature
differences between the higher latitudes and the equator are thought to
have resulted in drier conditions in the subtropics.
Independent multiproxy analyses of Raraku Lake (sedimentology,
mineralology, organic and inorganic geochemistry, etc.) indicate that Easter Island
was subject to two phases of arid climate that led to drought. The
first occurred between 500 and 1200, and the second occurring during the
Little Ice Age from 1570 to 1720. In between both arid phases, the island enjoyed a humid period from 1200 to 1570. That coincided with the peak of the Rapa Nui civilization.
Tree-ring data from Patagonia show cold episodes from 1270 and 1380 and from 1520 to 1670, during the events in the Northern Hemisphere. Eight sediment cores taken from Puyehue Lake
have been interpreted as showing a humid period from 1470 to 1700,
which the authors describe as a regional marker of the onset of the
Little Ice Age.
A 2009 paper details cooler and wetter conditions in southeastern South
America between 1550 and 1800 by citing evidence obtained via several
proxies and models. 18O records from three Andean ice cores show a cool period from 1600 to 1800.
Although it is only anecdotal evidence, the Antonio de Vea expedition entered San Rafael Lake in 1675 through Río Témpanos (Spanish for "Ice Floe River"). The Spanish mentioned no ice floe but stated that the San Rafael Glacier did not reach far into the lagoon. In 1766, another expedition noticed that the glacier reached the lagoon and calved into large icebergs. Hans Steffen
visited the area in 1898 and noticed that the glacier penetrated far
into the lagoon. Such historical records indicate a general cooling in
the area between 1675 and 1898: "The recognition of the LIA in northern
Patagonia, through the use of documentary sources, provides important,
independent evidence for the occurrence of this phenomenon in the
region." As of 2001, the borders of the glacier had significantly retreated from those of 1675.
It has been suggested that all glaciers of Gran Campo Nevado next to the Strait of Magellan reached their largest extent of the whole Holocene epoch during the Little Ice Age.
It has been proposed that the Little Ice Age, locally lasting
from the 17th to the 19th centuries, may have had a negative impact on
the productivity of marine ecosystems and on the navigability of the Patagonian fjords and channels being thus detrimental to the sea-faring Kawésqar.
Middle East
The
Ottoman LIA occurred from the early 14th century until the mid-19th
century, with its most intense phase taking place between the 16th and
17th centuries.
From the 14th to 15th century, the Ottoman Empire transformed from a small group of soldiers to a major world power. By the end of the 16th century, the LIA began
and had a profound impact on the Ottoman economy, society, and culture.
During February 1621, it is noted that the Bosphorus Strait in Istanbul
had frozen over completely.
In the years 1265, 1277 and 1297–1298 Byzantine sources describe
extremely harsh cold. Also, around 1300, there were harsh winters in
1298/1299 in the Middle East.
This is followed by a drought which takes place in Asia Minor in
1302-1304 while there is the flooding of the Sangarious River in the
summer of 1302.
The Ottoman Empire, whose territories stretched across three
continents, and its economy was based on agriculture and trade, had a
diverse range of climates and ecosystems, and was greatly affected by
this phenomenon.
The Ottoman Empire was one of the largest and most powerful empires in
the world during the Little Ice Age. The effects of the Little Ice Age
on the Ottoman Empire were significant, leading to changes in
agricultural practices, increased food prices, and social unrest. During
the 1590s the beginning of a wave of extremely cold winters began and
the middle eastern longest drought in six centuries marked the beginning
of the Little Ice Age in the Middle East. Due to the expansion of the Ottoman Empire in the late 16th century, the population of the empire reached around 30 million people which led to a shortage of land and an increase in tax.
The second half of the 16th century included inflation and rising cost
in both the Middle East and Europe. The effect of this large population
and lack of supplies created a strain on the Ottoman government.
The cooling climate disrupted agricultural production, leading to
food shortages and famines. The Ottoman Empire did not often have a
shortage of grain due to its location, close to the Danube, Nile and the
Black Sea, however, once the Little Ice Age began that all changed, and
grain was rare
due to the cooler temperatures which led to a shorter growing season,
resulting in lower crop yields and decreased food production. The
effects of the colder climate were exacerbated by extreme weather
events, such as droughts, floods, and storms, which further reduced crop
yields.
Each ancient Middle Eastern empire had a significant supply of food:
the Byzantines had Anatolia and Syria, the 'Abbasids had the lower
Tigris-Euphrates region, as well as Khurasan and Bukhara, and the
Ottomans had Egypt.
However, there was an inherent political risk in such agricultural
dependency, which finally materialised. Farmers who are unable or
unwilling to relocate may be driven into revolt against the established
authority if weather patterns shift. Nomads had the flexibility to move
in response to climate shifts, unlike settled peasants who weren't
willing to leave their traditional lands.
The impact of the Little Ice Age on the Ottoman Empire was not limited
to agriculture and trade. The cooling climate led to changes in
migration patterns, as some regions became uninhabitable while others
became more attractive. This in turn affected the demographics of the
empire and contributed to the emergence of new political and social
structures.
The lengthy drought as well as the cold winters led to the
destruction of imperial systems which all led to a series of uprisings
collectively known as the Celali Rebellion,
c. 1596–1610. The rebellion became the longest-lasting internal
challenge to state power in the Ottoman Empire's six centuries of
existence.
The goal of the Celali Rebellion was not to overthrow the Ottoman
government, instead it was an attempt to get newly appointed
governorships.
The Ottoman Empire did not fully recover from the Little Ice Age for
around a hundred years, even then they were considered weakened with a
large population loss.
Central England temperature series
Seasonal values of Central England temperatures. The top panel shows group sunspot
numbers: the grey area shows the annual values from telescopic
observations, the mauve line its 11-year running means, and the green
line the values deduced from the abundance of the Carbon-14cosmogenic isotope in tree trunks. The second panel shows the winter values of Central England temperature,
being the mean for December, January and February. The third panel
shows the summer values, being the mean for June, July and August. The
bottom panel gives the aerosal optical depth,
showing volcanic dust levels, from ice sheet cores. The vertical mauve
lines are years in which frost fairs were held on the Thames in London
and the vertical orange lines are the years when the ice there was
reported as thick enough to walk on. The first cyan line is the date of
the removal of the old London Bridge
and wier and the second is the completion of the embankments: both
riverine developments that increased the flow and ended Thames freezing
events. All data sources are given in reference
The Central England temperature
(CET) is the longest instrumental temperature record in existence
anywhere in the world, and extends back continuously from the present
day to 1659. Hence it starts in the middle of the Little Ice Age (LIA),
however the LIA interval is defined. CET holds some very important
implications for our understanding of the LIA. The CET data show that
during the LIA there was an increased occurrence of exceptionally cold
winters and these years coincided with years when frost fairs were held
on the Thames and when exceptionally low temperatures were reported
elsewhere in Europe. It also agrees well with paleoclimate estimates in average trends.
However, winters were not unremittingly cold during the LIA in the CET
record. For example, the coldest winter (defined by the average
temperature for December, January and February) in the whole CET data
series is 1684 (the year of one of the most famous frost fairs) yet the
fifth warmest winter in the whole CET data series to date occurred just
two years later, in 1686. Furthermore, summer temperatures are not
greatly depressed during the LIA and when they are these lower
temperatures correlate highly with volcanic eruptions.
Hence the CET data strongly argue that the LIA, at least in Europe,
should be regarded as a period of enhanced occurrence of exceptionally
cold winters and hence lower average temperatures and not as an interval
of unremitting cold.
Possible causes
Scientists have tentatively identified seven possible causes of the Little Ice Age: orbital cycles, decreased solar activity, increased volcanic activity, altered ocean current flows, fluctuations in the human population in different parts of the world causing reforestation or deforestation, and the inherent variability of global climate.
Orbital forcing
from cycles in the Earth's orbit around the Sun has for the past 2,000
years caused a long-term northern hemisphere cooling trend, which
continued through the Middle Ages and the Little Ice Age. The rate of Arctic cooling is roughly 0.02 °C per century. That trend could be extrapolated to continue into the future and possibly lead to a full ice age, but the 20th-century instrumental temperature record shows a sudden reversal of that trend, with a rise in global temperatures attributed to greenhouse gas emissions.
Solar activity
The Maunder Minimum in a 400-year history of sunspot numbersSunspot
number compared with Northern Hemisphere (NH) temperature anomaly. The
upper panel shows 11-year smoothed group sunspot numbers from telescopic
observations and the sunspot number derived from carbon-14 cosmogenic
isotope abundances in tree trunks. The lower panel shows the Northern
Hemisphere (NH) temperature anomaly (relative to the 1990 level) from a
wide variety of paleoclimate proxies: the black line is the mean value,
and the colors give the uncertainty probability distribution. The blue
dots are the instrumental record. The dashed lines mark the start and
end of the Little Ice Age (LIA) defined by the (NH) temperature anomaly
level -0.16 degrees Celsius.
Solar activity includes any disturbances on the Sun such as sunspots
and solar flares associated with the variable magnetic field of the
solar surface and solar atmosphere (corona). Because Alfvén's theorem applies, the coronal magnetic field is dragged out into the heliosphere by the solar wind. Irregularities in this heliospheric magnetic field shield Earth from galactic cosmic rays
by scattering them, which allows scientists to track solar activity in
the past by analyzing both the carbon-14 or beryllium-10 isotopes
generated by cosmic rays hitting the atmosphere and which are deposited
in terrestrial reservoirs such as tree rings and ice sheets. In the
intervals 1400–1550 (the Spörer Minimum) and 1645–1715 (the Maunder Minimum)
there were very low recorded levels of solar activity and they are both
within, or at least overlapped with, the LIA for most definitions.
However, solar activity deduced from cosmogenic isotopes was as high
between the Spörer Minimum and the Maunder Minimum as it was in about
1940, yet this interval is also within the LIA. Hence any relationship between solar activity and the LIA is far from a simple one.
A drop in solar activity circa 1230 AD as measured by biogenic silica corrected ignition residue (IR-BSi)
has been suggested by one study as a forcing potentially responsible
for initiating the LIA, with the authors noting that this drop in solar
output preceded the onset of significant volcanism.
A study by Dmitri Mauquoy et al. confirmed that at the beginning
of the Spörer Minimum, the carbon-14 production rate rose rapidly.
These authors argued this rise coincided with a sharp drop in
temperatures deduced from European peat bogs. This temperature drop is
also seen in mean northern hemisphere temperatures deduced from a wide
variety of paleoclimate indicators but the timing of the onset of the
Spörer Minimum is actually some 50 years earlier.
A 50-year response lag is possible but is not consistent with
subsequent variations in inferred solar activity and average northern
hemisphere temperature.
For example, the peak in solar activity between the Spörer Minimum and
the Maunder Minimum is 50 years after the only peak in average northern
hemisphere temperature that it could be associated with.
A study by Judith Lean in 1999 also pointed to a relationship between the Sun and the Little Ice Age. Her research found that there was a 0.13% total solar irradiance (TSI) increase ()
over 1650–1790 which could have raised the temperature of the Earth by
0.3 °C. In the calculated correlation coefficients of the global
temperature response to their reconstruction of the solar forcing over
three different periods, they found an average coefficient of 0.79 (i.e.
62% of the variation could be explained by the TSI) which indicates a
possible relationship between the two components. Lean's team also
formulated an equation in which the temperature change is 0.16 °C
increase in temperature for every 0.1% increase in total solar
irradiance.
However, the main problem with quantifying the longer-term trends in
TSI lies in the stability of the absolute radiometry measurements made
from space, which has improved since the pioneering work of Judith Lean
discussed above, but still remains a problem.
Analysis comparing trends in modern observations of TSI and cosmic ray
fluxes shows that the uncertainties mean that it is possible that TSI
was actually higher in the Maunder Minimum than present-day levels, but
uncertainties are high with best estimates of the difference between the
modern-day TSI and the Maunder-Minimum TSI in the range ± but with a uncertainty range of ±.
At the center of the LIA, during the Spörer Minimum and the Maunder Minimum,
sunspots were minimal and cosmogenic isotope deposition (carbon-14 and
beryllium-10) was increased in these minima as a result. However,
detailed studies from multiple paleoclimate indicators show that the
lower Northern Hemisphere temperatures in the Little Ice Age began
before the start of the Maunder Minimum
but after the start of the Spörer Minimum and persisted until after the
Maunder Minimum (and even after the much weaker Dalton Minimum) had
ceased. The return to more active solar conditions between these two
grand solar minima had no obvious effect on either global or Northern
Hemisphere temperatures. The Central England Temperature
provide evidence that low solar activity may have contributed to the
LIA through the increased occurrence of cold winters, at least in
Europe, but colder summers are more correlated with volcanic activity. Comparison of TSI records with Greenland ice core δ18O trends suggests that solar activity only accounted for 55% of the observed trend variance.
Numerical climate modelling indicates that volcanic activity was the
greater driver of the overall lower temperatures in the LIA, as seen in a
variety of paleoclimate proxies.
In a 2012 paper, Miller et al. link the Little Ice Age to an
"unusual 50-year-long episode with four large sulfur-rich explosive
eruptions, each with global sulfate loading >60 Tg" and notes that
"large changes in solar irradiance are not required."
Throughout the LIA, there was heightened volcanic activity. When a volcano
erupts, its ash reaches high into the atmosphere and can spread to
cover the whole earth. The ash cloud blocks out some of the incoming
solar radiation, which leads to worldwide cooling for up to two years after an eruption. Also emitted by eruptions is sulfur in the form of sulfur dioxide. When sulfur dioxide reaches the stratosphere, the gas turns into sulfuric acid particles, which reflect the Sun's rays. That further reduces the amount of radiation reaching the Earth's surface.
A recent study found that an especially severe tropical volcanic eruption in 1257, possibly Mount Samalas (pre-caldera edifice of the active Rinjani) near Mount Rinjani, both in Lombok,
Indonesia, followed by three smaller eruptions in 1268, 1275, and 1284,
did not allow the climate to recover. That may have caused the initial
cooling, and the 1452/1453 mystery eruption triggered a second pulse of cooling. The cold summers can be maintained by sea-ice/ocean feedbacks long after volcanic aerosols are removed.
Thermohaline circulation or Oceanic conveyor belt illustrated
In the early 2000s, a slowing of thermohaline circulation was proposed as an explanation for the LIA, specifically, through the weakening of the North Atlantic Gyre.
The circulation could have been interrupted by the introduction of a
large amount of fresh water into the North Atlantic and might have been
caused by a period of warming before the LIA that is known as the Medieval Warm Period. Some researchers have thus classified the LIA as a Bond event. In 2005 there was some concern that a shutdown of thermohaline circulation could happen again as a result of the present warming.
More recent research indicates that the overall Atlantic
Meridional Overturning Circulation may already be weaker now than it was
during the LIA, or perhaps even over the past millennium. While there is still a robust debate about the present-day AMOC strength,
these findings make the link between AMOC and the LIA unlikely.
However, some research instead suggests that a far more localized
disruption of the North Subpolar Gyre convection was involved in the LIA. This is potentially relevant for the near future, as a minority of climate models project a permanent collapse of this convection under some scenarios of future climate change.
Decreased human populations
Some researchers have proposed that human influences on climate began earlier than is normally supposed (see Early anthropocene
for more details) and that major population declines in Eurasia and the
Americas reduced that impact and led to a cooling trend.
The Black Death in Europe
The Black Death is estimated to have killed 30% to 60% of the European population.
In total, the plague may have reduced the world population from an
estimated 475 million to 350–375 million in the 14th century. It took 200 years for the world population to recover to its previous level. William Ruddimanet al.
proposed that those large population reductions in Europe, East Asia,
and the Middle East caused a decrease in agricultural activity that
allowed reforestation to cause additional carbon dioxide uptake from the atmosphere, leading to LIA cooling.
Destruction of native populations and biomass of the Americas
William Ruddiman further hypothesized that a reduced population in the Americas after European contact started in the 16th century could have had a similar effect.
In a similar vein, Koch and others in 1990 suggested that as European
conquest and disease brought by Europeans killed as many as 90% of
Indigenous Americans, around 50 million hectares of land may have
returned to a wilderness state, causing increased carbon dioxide uptake.
Other researchers have supported depopulation in the Americas as a
factor and have asserted that humans cleared considerable amounts of
forest to support agriculture there before the arrival of Europeans
brought on a population collapse.
Richard Nevle, Robert Dull and colleagues further suggested not
only that anthropogenic forest clearance played a role in reducing the
amount of carbon sequestered in Neotropical
forests but also that human-set fires played a central role in reducing
biomass in Amazonian and Central American forests before the arrival of
the Europeans and the concomitant spread of diseases during the Columbian exchange. Dull and Nevle calculated that reforestation in the tropical biomes of the Americas alone from 1500 to 1650 accounted for net carbon sequestration of 2–5 Pg.
Brierley conjectured that the European arrival in the Americas caused
mass deaths from epidemic disease, which caused much abandonment of
farmland. That caused much forest to return, which sequestered more CO2. A study of sediment cores and soil samples further suggests that CO2 uptake via reforestation in the Americas could have contributed to the LIA. The depopulation is linked to a drop in CO2 levels observed at Law Dome, Antarctica.
Population increases at mid- to high latitudes
It is suggested that during the Little Ice Age, increased deforestation had enough effect on the Earth's albedo
(reflectiveness) to cause regional and global temperature decreases.
Changes in albedo were caused by widespread deforestation at high
latitudes, which exposed more snow cover and thus increased
reflectiveness of the Earth's surface, as land was cleared for
agricultural use. The theory implies that over the course of the Little
Ice Age, enough land was cleared to make deforestation a possible cause
of climate change.
It has been proposed that the Land Use Intensification theory
could explain this effect. The theory was originally proposed by Ester
Boserup and suggests that agriculture advances only as the population
demands it. Furthermore, there is evidence of rapid population and agricultural expansion, which could warrant some of the changes observed in the climate during this period.
This theory is still under speculation for multiple reasons:
primarily, the difficulty of recreating climate simulations outside of a
narrow set of land
in those regions; so that one cannot rely on data to explain sweeping
changes or to account for the wide variety of other sources of climate
change globally. As an extension of the first reason, climate models
including this period have shown increases and decreases in temperature
globally.
That is, climate models have shown deforestation as neither a singular
cause for climate change nor a reliable cause for the global temperature
decrease.
Inherent variability of climate
Spontaneous
fluctuations in global climate might explain the past variability. It
is very difficult to know what the true level of variability from
internal causes might be given the existence of other forces, as noted
above, whose magnitude may not be known. One approach to evaluating
internal variability is the use of long integrations of coupled
ocean-atmosphere global climate models.
They have the advantage that the external forcing is known to be zero,
but the disadvantage is that they may not fully reflect reality. The
variations may result from chaos-driven changes in the oceans, the atmosphere, or interactions between the two. Two studies have concluded that the demonstrated inherent variability was not great enough to account for the Little Ice Age. The severe winters of 1770 to 1772 in Europe, however, have been attributed to an anomaly in the North Atlantic oscillation.
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