Desert greening

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Desert_greening

A satellite image of the Sahara, the world's largest hot desert and third largest desert after Antarctica and the Arctic

Desert greening is the process of afforestation or revegetation of deserts for ecological restoration (biodiversity), sustainable farming and forestry, but also for reclamation of natural water systems and other ecological systems that support life. The term "desert greening" is intended to apply to both cold and hot arid and semi-arid deserts (see Köppen climate classification system). It does not apply to ice capped or permafrost regions. It pertains to roughly 32 million square kilometres of land. Deserts span all seven continents of the Earth and make up nearly a fifth of the Earth's landmass, areas that recently have been increasing in size.

As some of the deserts expand and global temperatures increase, the different methods of desert greening may provide a possible response. Planting suitable flora in deserts has a range of environmental benefits from carbon sequestration to providing habitat for desert fauna to generating employment opportunities to creation of habitable areas for local communities.

The prevention of land desertification is one of 17 Sustainable Development Goals outlined by the United Nations. Desert greening is a process that aims to not only combat desertification but to foster an environment where plants can create a sustainable environment for all forms of life while preserving its integrity.

Desert greening techniques

When establishing or re-establishing vegetation in desert ecosystems there are many factors to consider before implementing a specific strategy. It is important to account for factors such as the geographical location of the area, amount of annual precipitation, average temperature, soil quality, nutrient availability, native plant and animal life, along with the human impact when aiming to restore a degraded or disrupted desert biome.

Planting

Planting strategies in the desert are different from conventional planting practices, especially in the initial stages. Deserts are regions in which annual precipitation is considerably less than the evaporation, making it difficult for plants and animals that are not specialized to the biome to survive. One of the ways to ensure the success of the plant life is that prior to being planted in the desert, plants are often grown first in greenhouses, allowing for root systems to develop. Often the plant species that are planted in desert regions are those that are capable of surviving on limited water and able to withstand the sun's direct rays. However, deserts also vary, with some being hot and dry and others being semiarid, and plants that may survive in a coastal desert might not be able to endure the considerably higher temperatures of hot and dry deserts. Therefore, when planting in deserts as an effort to restore the ecosystem or to create a greener space it is important that the vegetation being planted is suitable to the desert in which it is being planted.

Reversing desertification of Mu Us Desert west of Yulin, Shaanxi. 1985 (above) and 2021 situation.

Utilizing pioneer desert species like the Acamptopappus shockleyi or Lepidium fremontii which are native to the Mojave Desert, and halophytes such as Salicornia contribute positively to desert greening efforts. Planting of trees which store water, inhibit soil erosion through wind, raise water from underlying aquifers, reduce evaporation after a rain, attract animals (and thereby fertility through feces), and they can cause more rain to fall (by temperature reduction and other effects), if the planted area is large enough. Another method of introducing or re-introducing vegetation to deserts is through seeding which involves the scattering of seeds either manually or aerially depending upon the size of the region undergoing vegetation efforts. Using seeding as a desert greening technique on a large scale requires a longer time for the ecosystem to recover and for the vegetation to establish itself as was seen in the Mu Us Desert. Additionally, there are potential downsides due to the environmental vulnerability and predation by desert animals putting the success of this technique at risk.

Landscaping and green infrastructure

With the growth of human population in urban areas that are located close to deserts, ecoscaping has become an important strategy when designing and building infrastructure. Using the National Tree Benefit Calculator software it was established that if Acacia tortilis, Ziziphus spina-christi, and Phoenix dactylifera were planted in a desert city like Doha, this would yield a host of environmental benefits along with economic gains including carbon sequestration, air pollution reduction, lowering of the urban heat index, prevention of storm water runoff and increase in property values. As global temperatures increase, environmental impacts are considerably greater in dry regions with reduced precipitation levels which are vulnerable to desertification. Some of the effects that are beneficial for desert-greening which trees offer can also be provided by buildings that have incorporated architectural elements that allow them to shade exposed walls consequently reducing the heat absorption by the building. Another example of a building designed to offer beneficial effects of vegetation in the desert is the IBTS Greenhouse.

Agriculture

Desert farming also known as desert agriculture or arid farming, refers to the practice of cultivating and growing crops in arid or desert regions where water scarcity and extreme climatic conditions pose significant challenges to traditional agriculture. Desert farming involves employing various techniques with the help of technology to overcome the agricultural limitations imposed by an arid environment. Some common approaches used in desert farming include water management, soil improvement, crop selection, shade and windbreaks, greenhouses and controlled environments. Overall, desert farming aims to maximize the efficient use of water resources while improving soil quality, and planting crops suitable to the environment to overcome the challenges of arid environments. This allows farmers to cultivate crops and sustain agricultural production in regions traditionally considered inhospitable for farming.

Greenhouse cultivation also known as greenhouse farming or controlled environment agriculture, refers to the practice of cultivating plants within an enclosed structure called a greenhouse. It is a method of crop production that involves creating a controlled environment to optimize plant growth and protect crops from external factors such as extreme weather conditions, pests, and diseases. In a greenhouse, various environmental factors such as temperature, humidity, light intensity, and carbon dioxide levels can be monitored and adjusted to create ideal growing conditions for plants. This is achieved using various technologies such as heating and cooling systems, ventilation, irrigation systems, artificial lighting, and pest control measures. Greenhouses are typically made of transparent materials like glass or plastic, which allow sunlight to enter while trapping heat inside. This helps maintain a warmer temperature compared to the outside environment, extending the growing season and enabling the cultivation of plants that are not naturally suited to the local climate.

Seawater greenhouses are innovative systems that use seawater to grow crops in arid and water-scarce regions. These greenhouses employ a combination of evaporative cooling, humidification, and desalination techniques to create a controlled environment for plant growth. One prominent example of a seawater greenhouse is the Seawater Foundation. The Seawater Foundation is a non-profit organization that aims to address global food and water scarcity by utilizing seawater greenhouses. Their greenhouse system uses evaporative cooling to create a humid atmosphere for crops while seawater is used for humidification and cooling purposes. Another notable example is the IBTS (Integrated Biosphere Tectonics Systems) Greenhouse, developed by Seawater Greenhouse Ltd, the IBTS Greenhouse utilizes seawater to cool and humidify the air inside the greenhouse. It incorporates solar desalination systems to convert seawater into freshwater, which is then used to irrigate the plants. The concept of seawater greenhouses offers several advantages. Firstly, it allows for the cultivation of crops in arid regions with limited freshwater availability, reducing the pressure on traditional freshwater sources. Secondly, the humid and cooler environment created within these greenhouses promotes efficient plant growth, even in hot climates. Lastly, the evaporative cooling process can potentially produce freshwater as a byproduct, contributing to water sustainability. By harnessing the power of seawater and innovative greenhouse technologies, these initiatives are contributing to sustainable agriculture and addressing the challenges posed by water scarcity and climate change.

Water resources management

Water availability

Lake Tuendae, an artificial pond at Zzyzx Desert Studies Center in the Mojave Desert

Desert greening is substantially a function of water availability. Water can be made available through saving, reusing, rainwater harvesting, desalination, or direct use of seawater for salt-loving plants. Reuse of treated water and the closing of cycles is the most efficient because closed cycles stand for unlimited and sustainable supply – rainwater management is a decentralized solution and applicable for inland areas – desalination is very secure as long as the primary energy for the operation of the desalination plant is available. In the Sahara Forest Project desalination is carried out by solar stills for the generation of the freshwater. Another technique that is used is cloud seeding which helps in producing precipitation in areas with dryer climates. With the new techniques and latest technology used to produce rainfall in areas that had dryer climates, there are often floods due to the urban infrastructure in those areas being insufficient for precipitation that exceeds conventional levels. Dehumidification is a technique that uses "atmospheric water generation" or air to water, used by the military for potable water generation. However, this technology uses 200 times more energy than desalination, making it unsuitable for large scale desert greening.

Rainwater Harvesting

Collecting rainwater and storing it in ponds, reservoirs, or underground tanks is one of the simplest ways to improve soil moisture content, helping to increase green cover and crop production in arid areas. It is an effective method for increasing water availability in arid regions and can contribute to desert greening in several ways, such as increasing soil moisture so that farmers have a reliable water source for their crops, even during periods of low rainfall. Also, it plays an important role in recharging groundwater, since in many arid areas the groundwater is easily depleted, which could further exacerbate the aridity. This can help to combat desertification, reduce soil erosion, and promote biodiversity. Additionally, it helps alleviate water scarcity in areas with limited access to reliable water sources. Rainwater harvesting can serve as a practical and sustainable solution. It reduces the stress on scarce water resources, such as rivers or underground wells, and it provides a decentralized water supply system. Overall, rainwater harvesting contributes to desert greening by increasing soil moisture, promoting vegetation growth, and conserving water resources. It is a cost-effective and environmentally friendly technique that can be implemented at various scales, from individual households to large-scale agricultural systems to make desert areas more productive and sustainable.

Water distribution

The fresh water or seawater contained in centralized systems may be distributed by canals or in some instances aqueducts (both options cause water to evaporate due to environmental exposure), troughs (as used in the Keita Project), earthenware piping (semi-open or closed) or even underground systems like qanāt. The mode of water distribution influences how its distribution to plants, which include drip irrigation (used only in pipes) a costly solution, wadis (V-shaped ponds dug in the earth) or by simply planting the trees in holes inside/over the water pipe itself allowing the roots access to the water straight from the pipe (used in qanāt, hydroponics etc.). Water can also be distributed through semi-open pipes as seen in the dug throughs in the Keita Project.

Disadvantages

The use of water for desert greening in arid regions, however, is not without its disadvantages. Desert greening by the Helmand and Arghandab Valley Authority irrigation scheme in Afghanistan significantly reduced the water flowing from the Helmand River into Lake Hamun and this, together with drought, was cited as a key reason for the severe damage to the ecology of Lake Hamun, much of which has degenerated since 1999 from a wetland of international importance into salt flats. Similarly in northwestern China, desert greening practices fueled by economic and environmental benefits, resulted in the exhaustion of the groundwater sources which impacted soil integrity.

History

Reforestation in the Kubuqi Desert, China

The practice of recent desert greening can be traced back to a Japanese horticulture professor and agriculturist, Seiei Toyama, who spent 30 years of his life in efforts to green the Kubuqi Desert in China. He authored the text Greening the Deserts: Techniques and Achievements of Two Japanese Agriculturists along with Masao Toyama which was published in 1995. During his time as a professor at Tottori University, Toyama was able to revitalize the surrounding sandy dunes into revenue generating farms through his irrigation techniques and knowledge of plant species. After his retirement in 1972, he pursued agricultural projects in China which included the conservation of eroding banks of Yellow River by planting Kudzu vines, introduction of grape growing techniques in Ningxia Huizu Autonomous Region, and his most well known project in the Engebei Desert Development, an oasis in the Kubuqi Desert of Inner Mongolia.

Examples

Asia

The history of modern desert greening in Asia focuses on initiatives that are aimed at reducing desertification and promoting sustainable land management practices. However, the challenges faced by nations in the Asian continent are varied, and the solutions have been tailored to meet specific needs. One of the earliest and most notable examples of desert greening in Asia occurred in China in the 1970s, the "Green Great Wall" program, aimed at planting trees along the border of the Gobi Desert to halt its expansion. The program involved planting over 100 billion trees across a thousand miles of desert within a decade. The initiative was successful in reducing sandstorms and increasing rainfall in the region, and the program has since been expanded to other parts of China. In the Middle East, Israel's desert greening initiatives have been aimed at the Negev Desert. Initiatives include the establishment of research and development centers for desert agriculture, the introduction of drip irrigation techniques, and the use of treated wastewater for irrigation. In the Indian subcontinent, India and Pakistan's desert greening initiatives have focused on afforestation and soil conservation. These initiatives involve planting trees, shrubs, and grasses to hold the soil in place, prevent erosion, and improve water retention. Overall, the history of modern desert greening in Asia reflects the need to address environmental challenges such as desertification and promote sustainable land management practices. These initiatives have often been successful in addressing these challenges and improving the livelihoods of people in arid regions.

China

Main article: Great Green Wall (China)

China's Green Great Wall Program

The Three-North Shelter Forest Program, also nicknamed the "Great Green Wall", is a series of windbreaking forests in China designed to hold back the expansion of the Gobi Desert and reduce the incidence of dust storms that have long caused problems for northern China, as well as also providing timber to the local population. The program started in 1978 with the proposed end result of raising northern China's forested area from 5 to 15 percent, and is planned to be completed around 2050, at which point it will be 4,500 km (2,800 mi) long. In 2008, winter storms destroyed 10% of the new forest stock, causing the World Bank to advise China to focus more on quality rather than quantity in its stock species.

As of 2009, China's planted forest covered more than 500,000 km² (190,000 sq mi), increasing tree coverage from 12% to 18%. It is the largest artificial forest in the world. According to Foreign Affairs, the program successfully transitioned the economic model in the Gobi Desert region from ecologically harmful industrial farming and pastoralism to beneficial ecotourism, fruticulture and forestry. In 2018, United States' National Oceanic and Atmospheric Administration found the increase in forest coverage observed by satellites is consistent with the Chinese government data. According to Shixiong Cao, an ecologist at Beijing Forestry University, the Chinese Government recognized the water shortage problems in arid regions and changed the approach towards vegetation with lower water requirements. Zhang Jianlong, head of the Forestry Department, told the media that the goal was to sustain the health of vegetation and choose suitable plant species and irrigation techniques.

According to BBC News report in 2020, China's tree plantation programs resulted in significant carbon fixation and helped mitigated climate change, and the benefit was underestimated by previous research. The program also reversed the desertification of the Gobi desert, which grew 10,000 km² (3,900 sq mi) per year in the 1980s, but had shrunk by more than 2,000 km² (770 sq mi) in 2022.

India

The soil of the Thar Desert in India remains dry for much of the year and is prone to soil erosion. High speed winds blow the soil from the desert, depositing it on neighboring fertile lands, and causing shifting sand dunes within the desert which bury fences and block roads and railway tracks. A permanent solution to shifting sand dunes can be provided by planting appropriate species on the dunes to prevent further movement and planting windbreaks and shelterbelts. These solutions also provide protection from hot or cold and desiccating winds and the invasion of sand. The Rajasthan Canal system in India is the major irrigation scheme of the Thar Desert and is intended to reclaim it.

There are few local tree species suitable for planting in the desert region and they are slow growing. Introduction of exotic tree species in the desert has become a necessity, many species of Eucalyptus, Acacia, Cassia and other genera from Israel, Australia, US, Russia, Zimbabwe, Chile, Peru, and Sudan have been tried in the Thar Desert. Vachellia tortilis has proved to be the most promising species for desert greening in this region. Prevention of shifting sand dunes can be accomplished through planting trees like the Vachellia tortilis near Laxmangarh town. Another promising species is jojoba which is economically valuable as well.

Africa

Main article: Great Green Wall (Africa)

Modern desert greening in Africa is a relatively recent phenomenon and was primarily initiated in the 1950s and 1960s. The initiative was largely driven by a desire to combat desertification, the process by which fertile land becomes barren and unsuitable for farming, across the continent. One of the earliest and most notable examples of desert greening in Africa occurred in Algeria. In the 1950s, the Algerian government launched an ambitious program to transform over 20,000 square kilometers of arid land into productive agricultural land. This project involved the construction of dams, wells, and irrigation networks, as well as the introduction of modern farming techniques and seed varieties. The program was part of a broader effort to address food insecurity and improve livelihoods in rural areas. In the following decades, similar projects were undertaken in other countries, such as Mali, Niger, and Senegal. These initiatives focused on promoting sustainable agriculture and land management practices, as well as reforestation and the protection of natural ecosystems. Some of the key strategies employed included the use of drought-resistant crops, the introduction of agroforestry techniques, and the establishment of community-based management systems. In recent years, desert greening efforts have also been boosted by the development of renewable energy technologies, such as solar and wind power. These technologies provide a sustainable source of energy for desert regions, which can be used to power irrigation systems and other farming equipment. Greening projects that integrate renewable energy solutions are often more effective and cost-efficient in the long run. Overall, modern desert greening in Africa has made significant progress in reducing the impact of desertification and improving the sustainability of agriculture and natural resource management in arid areas. However, many challenges remain, such as lack of funding, political instability, and climate change. As such, ongoing research and development of innovative strategies, including the integration of new technologies, will be essential for continued success in this area.

The "Great Green Wall of the Sahara and the Sahel" is a project adopted by the African Union in 2007, initially conceived as a way to combat desertification in the Sahel region and hold back expansion of the Sahara Desert by planting a wall of trees stretching across the entire Sahel from Djibouti City to Dakar. The original dimensions of the "wall" were slated to be 15 km (9.3 mi) wide and 7,775 km (4,831 mi) long, but the program has expanded to encompass nations in both North and West Africa. The modern green wall has since evolved into a program promoting water harvesting techniques, greenery protection and improving indigenous land use techniques, aimed at creating a mosaic of green and productive landscapes across North Africa. The ongoing goal of the project is to restore 100 million hectares of degraded land and capture 250 million tonnes of carbon dioxide, and create 10 million jobs in the process all by 2030.

As of March 2019, 15 per cent of the wall was complete with significant gains made in Nigeria, Senegal and Ethiopia. In Senegal, over 11 million trees had been planted. Nigeria has restored 4,900,000 ha (12,000,000 acres; 49,000 km²) of degraded land, and Ethiopia has reclaimed 15,000,000 ha (37,000,000 acres; 150,000 km²). A report commissioned by the United Nations Convention to Combat Desertification (UNCCD) was published on September 7, 2020, that the Great Green Wall had only covered 4% of the planned area, with only 4,000,000 ha (9,900,000 acres; 40,000 km²) planted. Ethiopia has had the most success with 5.5 billion seedlings planted, but Chad has only planted 1.1 million. Doubt was also raised over the survival rate of the 12 million trees planted in Senegal.

In January 2021, the project received a boost at the One Planet Summit, where its partners pledged 14.3 billion USD to launch the Great Green Wall Accelerator, aimed at facilitating the collaboration and coordination among donors and involved stakeholders across 11 countries. In September 2021, the French Development Agency estimated that 20 million hectares have been restored and 350,000 jobs have been created. According to the second edition of the Global Land Outlook' published by the UNCCD in April 2022, one reason the project has experienced implementation challenges is the political risk associated with investing in more fragile nations as well as the fact that many "GGW projects generate low economic returns compared to the significant environmental and social benefits accrued that often have little or no market value". Furthermore, international donors seem to favor investing in more stable nations, picking and choosing which projects they will fund, and leaving nations with less stable governments behind.

Australia

Australia is the world's driest inhabited continent, with a significant portion covered by arid or semi-arid deserts. In recent years, there have been various efforts and initiatives focused on desert greening in Australia. One notable example is the "Great Green Wall" project, inspired by similar initiatives in Africa, which aims to create a vegetation barrier of local native plants across Australia's east coast to prevent desertification and erosion. [Reference needed] Another approach to desert greening in Australia involves the use of regenerative farming and land management techniques. These techniques aim to restore degraded soils and improve water retention, which can support the growth of vegetation and increase biodiversity. [Reference needed] Additionally, there are ongoing research and development projects that explore innovative techniques to facilitate desert greening, such as solar-powered desalination plants, drought-resistant crop varieties, and the use of native plant species that can thrive in arid environments. [Reference needed] It's important to note that the success of desert greening initiatives depends on various factors, including local climate conditions, access to water resources, suitable plant species, and sustainable land management practices.

Sundrop Farms launched a greenhouse in 2016 to produce 15,000 tonnes of tomatoes using only desert soil and desalinated water piped from Spencer Gulf.

Land surface effects on climate

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Land_surface_effects_on_climate

Land surface effects on climate are wide-ranging and vary by region. Deforestation and exploitation of natural landscapes play a significant role. Some of these environmental changes are similar to those caused by the effects of global warming.

Deforestation effects

See also: Deforestation by region

Major land surface changes affecting climate include deforestation (especially in tropical areas), and destruction of grasslands and xeric woodlands by overgrazing, or lack of grazing. These changes in the natural landscape reduce evapotranspiration, and thus water vapor, in the atmosphere, limiting clouds and precipitation. It has been proposed, in the journal Atmospheric Chemistry and Physics, that evaporation rates from forested areas may exceed that of the oceans, creating zones of low pressure, which enhance the development of storms and rainfall through atmospheric moisture recycling. The American Institute of Biological Sciences published a similar paper in support of this concept in 2009. In addition, with deforestation and/or destruction of grasslands, the amount of dew harvested (or condensed) by plants is greatly diminished. All of this contributes to desertification in these regions.

25-50% of the rainfall in the Amazon basin comes from the forest, and if deforestation reaches 30-40% most of the Amazon basin will enter a permanent dry climate. In another article published by Nature, it points out that tropical deforestation can lead to large reductions in observed precipitation.

This concept of land-atmosphere feedback is common among permaculturists, such as Masanobu Fukuoka, who, in his book, The One Straw Revolution, said "rain comes from the ground, not the sky."

Deforestation, and conversion of grasslands to desert, may also lead to cooling of the regional climate. This is because of the albedo effect (sunlight reflected by bare ground) during the day, and rapid radiation of heat into space at night, due to the lack of vegetation and atmospheric moisture.

Reforestation, conservation grazing, holistic land management, and, in drylands, water harvesting and keyline design, are examples of methods that might help prevent or lessen these drying effects.

Mountain meteorological effects

Orographic lift

Main article: Orographic lift

Orographic lift occurs when an air mass is forced from a low elevation to a higher elevation as it moves over rising terrain. As the air mass gains altitude it quickly cools down adiabatically, which can raise the relative humidity to 100% and create clouds and, under the right conditions, precipitation.

Rain shadow

Main article: Rain shadow

A rain shadow is a dry area on the leeward side of a mountainous area (away from the wind). The mountains block the passage of rain-producing weather systems and cast a "shadow" of dryness behind them. Wind and moist air is drawn by the prevailing winds towards the top of the mountains, where it condenses and precipitates before it crosses the top. In an effect opposite that of orographic lift, the air, without much moisture left, advances behind the mountains creating a drier side called the "rain shadow".

Foehn wind

Main article: Foehn wind

A föhn or foehn is a type of dry, warm, down-slope wind that occurs in the lee (downwind side) of a mountain range.

Föhn can be initiated when deep low pressures move into Europe drawing moist Mediterranean air over the Alps.

It is a rain shadow wind that results from the subsequent adiabatic warming of air that has dropped most of its moisture on windward slopes (see orographic lift). As a consequence of the different adiabatic lapse rates of moist and dry air, the air on the leeward slopes becomes warmer than equivalent elevations on the windward slopes. Föhn winds can raise temperatures by as much as 14 °C (25 °F) in just a matter of minutes. Central Europe enjoys a warmer climate due to the Föhn, as moist winds off the Mediterranean Sea blow over the Alps.

Global cooling

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Global_cooling

Mean temperature anomalies during the period 1965 to 1975 with respect to the average temperatures from 1937 to 1946. This dataset was not available at the time.

Global cooling was a conjecture, especially during the 1970s, of imminent cooling of the Earth culminating in a period of extensive glaciation, due to the cooling effects of aerosols or orbital forcing. Some press reports in the 1970s speculated about continued cooling; these did not accurately reflect the scientific literature of the time, which was generally more concerned with warming from an enhanced greenhouse effect.

In the mid 1970s, the limited temperature series available suggested that the temperature had decreased for several decades up to then. As longer time series of higher quality became available, it became clear that global temperature showed significant increases overall.

Introduction: general awareness and concern

By the 1970s, scientists were becoming increasingly aware that estimates of global temperatures showed cooling since 1945, as well as the possibility of large scale warming due to emissions of greenhouse gases. In the scientific papers which considered climate trends of the 21st century, less than 10% were inclined towards future cooling, while most papers predicted future warming. The general public had little awareness of carbon dioxide's effects on climate, but Science News in May 1959 forecast a 25% increase in atmospheric carbon dioxide in the 150 years from 1850 to 2000, with a consequent warming trend. The actual increase in this period was 29%. Paul R. Ehrlich mentioned global warming from greenhouse gases as a counterforce to the cooling effect of aerosols in 1968. By the time the idea of global cooling reached the public press in the mid-1970s temperatures had stopped falling, and there was concern in the climatological community about carbon dioxide's warming effects. In response to such reports, the World Meteorological Organization issued a warning in June 1976 that "a very significant warming of global climate" was probable.

Currently, there are some concerns about the possible regional cooling effects of a slowdown or shutdown of thermohaline circulation, which might be provoked by an increase of fresh water mixing into the North Atlantic due to glacial melting. The probability of this occurring is generally considered to be very low, and the IPCC notes, "even in models where the THC weakens, there is still warming over Europe. For example, in all AOGCM integrations where the radiative forcing is increasing, the sign of the temperature change over north-west Europe is positive."

Physical mechanisms

The cooling period is reproduced by current (1999 on) global climate models that include the physical effects of sulfate aerosols, and there is now general agreement that aerosol effects were the dominant cause of the mid-20th century cooling. At the time there were two physical mechanisms that were most frequently advanced to cause cooling: aerosols and orbital forcing.

Aerosols

Main article: Particulates § Climate effects

Human activity — mostly as a by-product of fossil fuel combustion, partly by land use changes — increases the number of tiny particles (aerosols) in the atmosphere. These have a direct effect: they effectively increase the planetary albedo, thus cooling the planet by reducing the solar radiation reaching the surface; and an indirect effect: they affect the properties of clouds by acting as cloud condensation nuclei. In the early 1970s some speculated that this cooling effect might dominate over the warming effect of the CO₂ release: see discussion of Rasool and Schneider (1971), below. As a result of observations and a switch to cleaner fuel burning, this no longer seems likely; current scientific work indicates that global warming is far more likely. Although the temperature drops foreseen by this mechanism have now been discarded in light of better theory and the observed warming, aerosols are thought to have contributed a cooling tendency (outweighed by increases in greenhouse gases) and also have contributed to global dimming.

Orbital forcing

Main article: Orbital forcing

CO₂, temperature, and dust concentration measured by Petit et al. from Vostok ice core at Antarctica.

Orbital forcing refers to the slow, cyclical changes in the tilt of Earth's axis and shape of its orbit. These cycles alter the total amount of sunlight reaching the Earth by a small amount and affect the timing and intensity of the seasons. This mechanism is thought to be responsible for the timing of the ice age cycles, and understanding of the mechanism was increasing rapidly in the mid-1970s.

The paper of Hays, Imbrie, and Shackleton "Variations in the Earth's Orbit: Pacemaker of the Ice Ages" qualified its predictions with the remark that "forecasts must be qualified in two ways. First, they apply only to the natural component of future climatic trends - and not to anthropogenic effects such as those due to the burning of fossil fuels. Second, they describe only the long-term trends, because they are linked to orbital variations with periods of 20,000 years and longer. Climatic oscillations at higher frequencies are not predicted ... the results indicate that the long-term trend over the next 20,000 years is towards extensive Northern Hemisphere glaciation and cooler climate".

The idea that ice ages cycles were predictable appears to have become conflated with the idea that another one was due "soon" - perhaps because much of this study was done by geologists, who are accustomed to dealing with very long time scales and use "soon" to refer to periods of thousands of years. A strict application of the Milankovitch theory does not allow the prediction of a "rapid" ice age onset (i.e., less than a century or two) since the fastest orbital period is about 20,000 years. Some creative ways around this were found, notably one championed by Nigel Calder under the name of "snowblitz", but these ideas did not gain wide acceptance.

The length of the current interglacial temperature peak is similar to the length of the preceding interglacial peak (Sangamon/Eem), and so it could be concluded that we might be nearing the end of this warm period. This conclusion would be mistaken. Firstly, because the lengths of previous interglacials were not particularly regular; see figure. Petit et al. note that "interglacials 5.5 and 9.3 are different from the Holocene, but similar to each other in duration, shape and amplitude. During each of these two events, there is a warm period of 4 kyr followed by a relatively rapid cooling". Secondly, future orbital variations will not closely resemble those of the past.

Concern pre-1970s

In 1923, there was concern about a new ice age and Captain Donald Baxter MacMillan sailed toward the Arctic sponsored by the National Geographical Society to look for evidence of advancing glaciers.

In 1926, a Berlin astronomer was predicting global cooling but that it was "ages away".

Concerns that a new ice age was approaching was revived in the 1950s. During the Cold War, there were concerns by Harry Wexler that setting off atom bombs could be hastening a new ice age from a nuclear winter scenario.

J. Murray Mitchell showed as early as 1963 a multidecadal cooling since about 1940. At a conference on climate change held in Boulder, Colorado in 1965, evidence supporting Milankovitch cycles triggered speculation on how the calculated small changes in sunlight might somehow trigger ice ages. In 1966, Cesare Emiliani predicted that "a new glaciation will begin within a few thousand years." In his 1968 book The Population Bomb, Paul R. Ehrlich wrote "The greenhouse effect is being enhanced now by the greatly increased level of carbon dioxide ... [this] is being countered by low-level clouds generated by contrails, dust, and other contaminants ... At the moment we cannot predict what the overall climatic results will be of our using the atmosphere as a garbage dump."

Concern in the 1970s

1970s awareness

The temperature record as seen in 1975; compare with the next figure.

 

Global mean surface temperature change since 1880. Source: NASA GISS

Concern peaked in the early 1970s, though "the possibility of anthropogenic warming dominated the peer-reviewed literature even then"  (a cooling period began in 1945, and two decades of a cooling trend suggested a trough had been reached after several decades of warming). This peaking concern is partially attributable to the fact much less was then known about world climate and causes of ice ages. Climate scientists were aware that predictions based on this trend were not possible - because the trend was poorly studied and not understood (for example see reference). Despite that, in the popular press the possibility of cooling was reported generally without the caveats present in the scientific reports, and "unusually severe winters in Asia and parts of North America in 1972 and 1973 ... pushed the issue into the public consciousness".

In the 1970s, the compilation of records to produce hemispheric, or global, temperature records had just begun.

Spencer R. Weart's history of The Discovery of Global Warming says that: "While neither scientists nor the public could be sure in the 1970s whether the world was warming or cooling, people were increasingly inclined to believe that global climate was on the move, and in no small way" [emphasis added].

On January 11, 1970, The Washington Post reported that "Colder Winters Held Dawn of New Ice Age".

In 1972, Emiliani warned "Man's activity may either precipitate this new ice age or lead to substantial or even total melting of the ice caps".

Also in 1972, a group of glacial-epoch experts at a conference agreed that "the natural end of our warm epoch is undoubtedly near"; but the volume of Quaternary Research reporting on the meeting said that "the basic conclusion to be drawn from the discussions in this section is that the knowledge necessary for understanding the mechanism of climate change is still lamentably inadequate". George Kukla and Robert Matthews, in a Science write-up of a conference, asked when and how the current interglacial would end; concluding that, unless there were impacts from future human activity, "Global cooling and related rapid changes of environment, substantially exceeding the fluctuations experienced by man in historical times, must be expected within the next few millennia or even centuries", but many other scientists doubted these conclusions.

1970 SCEP report

The 1970 Study of Critical Environmental Problems reported the possibility of warming from increased carbon dioxide, but no concerns about cooling, setting a lower bound on the beginning of interest in "global cooling".

1971 to 1975: papers on warming and cooling factors

By 1971, studies indicated that human caused air pollution was spreading, but there was uncertainty as to whether aerosols would cause warming or cooling, and whether or not they were more significant than rising CO₂ levels. J. Murray Mitchell still viewed humans as "innocent bystanders" in the cooling from the 1940s to 1970, but in 1971 his calculations suggested that rising emissions could cause significant cooling after 2000, though he also argued that emissions could cause warming depending on circumstances. Calculations were too basic at this time to be trusted to give reliable results.

An early numerical computation of climate effects was published in the journal Science in July 1971 as a paper by S. Ichtiaque Rasool and Stephen H. Schneider, titled "Atmospheric Carbon Dioxide and Aerosols: Effects of Large Increases on Global Climate". The paper used rudimentary data and equations to compute the possible future effects of large increases in the densities in the atmosphere of two types of human environmental emissions:

1. greenhouse gases such as carbon dioxide;
2. particulate pollution such as smog, some of which remains suspended in the atmosphere in aerosol form for years.

The paper suggested that the global warming due to greenhouse gases would tend to have less effect with greater densities, and while aerosol pollution could cause warming, it was likely that it would tend to have a cooling effect which increased with density. They concluded that "An increase by only a factor of 4 in global aerosol background concentration may be sufficient to reduce the surface temperature by as much as 3.5 ° K. If sustained over a period of several years, such a temperature decrease over the whole globe is believed to be sufficient to trigger an ice age."

Both their equations and their data were badly flawed, as was soon pointed out by other scientists and confirmed by Schneider himself. In January 1972, Robert Jay Charlson et al. pointed out that with other reasonable assumptions, the model produced the opposite conclusion. The model made no allowance for changes in clouds or convection, and erroneously indicated that eight times as much CO₂ would only cause 2 °C of warming. In a paper published in 1975, Schneider corrected the overestimate of aerosol cooling by checking data on the effects of dust produced by volcanoes. When the model included estimated changes in solar intensity, it gave a reasonable match to temperatures over the previous thousand years and its prediction was that "CO₂ warming dominates the surface temperature patterns soon after 1980."

1972 and 1974 National Science Board

The National Science Board's Patterns and Perspectives in Environmental Science report of 1972 discussed the cyclical behavior of climate, and the understanding at the time that the planet was entering a phase of cooling after a warm period. "Judging from the record of the past interglacial ages, the present time of high temperatures should be drawing to an end, to be followed by a long period of considerably colder temperatures leading into the next glacial age some 20,000 years from now." But it also continued; "However, it is possible, or even likely, that human interference has already altered the environment so much that the climatic pattern of the near future will follow a different path."

The board's report of 1974, Science And The Challenges Ahead, continued on this theme. "During the last 20-30 years, world temperature has fallen, irregularly at first but more sharply over the last decade." Discussion of cyclic glacial periods does not feature in this report. Instead it is the role of humans that is central to the report's analysis. "The cause of the cooling trend is not known with certainty. But there is increasing concern that man himself may be implicated, not only in the recent cooling trend but also in the warming temperatures over the last century". The report did not conclude whether carbon dioxide in warming, or agricultural and industrial pollution in cooling, are factors in the recent climatic changes, noting; "Before such questions as these can be resolved, major advances must be made in understanding the chemistry and physics of the atmosphere and oceans, and in measuring and tracing particulates through the system."

1975 National Academy of Sciences report

There also was a Report by the U.S. National Academy of Sciences (NAS) entitled, "Understanding Climate Change: A Program for Action".

The report stated (p. 36) that, "The average surface air temperature in the northern hemisphere increased from the 1880s until about 1940 and has been decreasing thereafter."

It also stated (p. 44) that, "If both the CO₂ and particulate inputs to the atmosphere grow at equal rates in the future, the widely differing atmospheric residence times of the two pollutants means that the particulate effect will grow in importance relative to that of CO₂."

The report did not predict whether the 25-year cooling trend would continue. It stated (Forward, p. v) that, "we do not have a good quantitative understanding of our climate machine and what determines its course [so] it does not seem possible to predict climate", and (p. 2) "The climates of the earth have always been changing, and they will doubtless continue to do so in the future. How large these future changes will be, and where and how rapidly they will occur, we do not know."

The Report's "program for action" was a call for creation of a new National Climatic Research Program. It stated (p. 62), "If we are to react rationally to the inevitable climatic changes of the future, and if we are ever to predict their future course, whether they are natural or man-induced, a far greater understanding of these changes is required than we now possess. It is, moreover, important that this knowledge be acquired as soon as possible." For that reason, it stated, "the time has now come to initiate a broad and coordinated attack on the problem of climate and climatic change."

1974 Time magazine article

While these discussions were ongoing in scientific circles, other accounts appeared in the popular media. In their June 24, 1974, issue, Time presented an article titled "Another Ice Age?" that noted "the atmosphere has been growing gradually cooler for the past three decades" but noted that "Some scientists ... think that the cooling trend may be only temporary."

1975 Newsweek article

An April 28, 1975, article in Newsweek magazine was titled "The Cooling World", it pointed to "ominous signs that the Earth's weather patterns have begun to change" and pointed to "a drop of half a degree [Fahrenheit] in average ground temperatures in the Northern Hemisphere between 1945 and 1968." The article stated "The evidence in support of these predictions [of global cooling] has now begun to accumulate so massively that meteorologists are hard-pressed to keep up with it." The Newsweek article did not state the cause of cooling; it stated that "what causes the onset of major and minor ice ages remains a mystery" and cited the NAS conclusion that "not only are the basic scientific questions largely unanswered, but in many cases we do not yet know enough to pose the key questions."

The article mentioned the alternative solutions of "melting the Arctic ice cap by covering it with black soot or diverting Arctic rivers" but conceded these were not feasible. The Newsweek article concluded by criticizing government leaders: "But the scientists see few signs that government leaders anywhere are even prepared to take the simple measures of stockpiling food or of introducing the variables of climatic uncertainty into economic projections of future food supplies ... The longer the planners (politicians) delay, the more difficult will they find it to cope with climatic change once the results become grim reality." The article emphasized sensational and largely unsourced consequences - "resulting famines could be catastrophic", "drought and desolation", "the most devastating outbreak of tornadoes ever recorded", "droughts, floods, extended dry spells, long freezes, delayed monsoons", "impossible for starving peoples to migrate", "the present decline has taken the planet about a sixth of the way toward the Ice Age."

On October 23, 2006, Newsweek issued a correction, over 31 years after the original article, stating that it had been "so spectacularly wrong about the near-term future" (though editor Jerry Adler stated that "the story wasn't 'wrong' in the journalistic sense of 'inaccurate.'")

Other 1970s sources

Academic analysis of the peer-reviewed studies published at that time shows that most papers examining aspects of climate during the 1970s were either neutral or showed a warming trend.

In 1977, a popular book on the topic was published, called The Weather Conspiracy: The Coming of the New Ice Age.

1979 WMO conference

Later in the decade, at a WMO conference in 1979, F. Kenneth Hare reported:

Fig 8 shows ... 1938 the warmest year. They [temperatures] have since fallen by about 0.4 °C. At the end there is a suggestion that the fall ceased in about 1964, and may even have reversed.

Figure 9 challenges the view that the fall of temperature has ceased ... the weight of evidence clearly favours cooling to the present date ... The striking point, however, is that interannual variability of world temperatures is much larger than the trend ... it is difficult to detect a genuine trend

It is questionable, moreover, whether the trend is truly global. Calculated variations in the 5-year mean air temperature over the southern hemisphere chiefly with respect to land areas show that temperatures generally rose between 1943 and 1975. Since the 1960-64 period this rise has been strong ... the scattered SH data fail to support a hypothesis of continued global cooling since 1938. [p 65]

Late-20th-century cooling predictions

1980s

Concerns about nuclear winter arose in the early 1980s from several reports. Similar speculations have appeared over effects due to catastrophes such as asteroid impacts and massive volcanic eruptions.

1990s

In 1991, a prediction by Carl Sagan and other scientists who had worked on the famous TTAPS study on nuclear winter that massive oil well fires in Kuwait would cause significant effects on climate was incorrect.

In January 1999, contrarian Patrick Michaels wrote a commentary offering to "take even money that the 10 years ending on December 31, 2007, will show a statistically significant global cooling trend in temperatures measured by satellite", on the basis of his view that record temperatures in 1998 had been a blip. Indeed, over that period, satellite-measured temperatures never again approached their 1998 peak. Due to a sharp but temporary dip in temperatures in 1999–2000, a least-squares linear regression fit to the satellite temperature record showed little overall trend. The RSS satellite temperature record showed a slight cooling trend, but the UAH satellite temperature record showed a slight warming trend.

Twenty-first century

In 2003, the Office of Net Assessment at the United States Department of Defense was commissioned to produce a study on the likely and potential effects of abrupt modern climate change should a shutdown of thermohaline circulation occur. The study, conducted under ONA head Andrew Marshall, modelled its prospective climate change on the 8.2 kiloyear event, precisely because it was the middle alternative between the Younger Dryas and the Little Ice Age. Scientists said that "abrupt climate change initiated by Greenland ice sheet melting is not a realistic scenario for the 21st century".

Present level of knowledge

Main article: Next glacial period

The concern that cooler temperatures would continue, and perhaps at a faster rate, has been observed to be incorrect, as was assessed in the IPCC Third Assessment Report of 2001. More has to be learned about climate. However, the growing records have shown that short term cooling concerns have not been borne out.

As for the prospects of the end of the current interglacial, while the four most recent interglacials lasted about 10,000 years, the interglacial before that lasted around 28,000 years. Milankovitch-type calculations indicate that the present interglacial would probably continue for tens of thousands of years naturally in the absence of human perturbations. Other estimates (Loutre and Berger, based on orbital calculations) put the unperturbed length of the present interglacial at 50,000 years. A. Berger expressed the opinion in 2005 (EGU presentation) that the present CO₂ perturbation will last long enough to suppress the next glacial cycle entirely. This is consistent with the prediction of David Archer and colleagues who argued in 2005 that the present level of CO₂ will suspend the next glacial period for the next 500,000 years and will be the longest duration and intensity of the projected interglacial period and are longer than have been seen in the last 2.6 million years.

A 2015 report by the Past Global Changes Project, including Berger, says simulations show that a new glaciation is unlikely to happen within the next approximately 50,000 years, before the next strong drop in Northern Hemisphere summer insolation occurs "if either atmospheric CO₂ concentration remains above 300 ppm or cumulative carbon emissions exceed 1000 Pg C" (i.e. 1000 gigatonnes carbon). "Only for an atmospheric CO₂ content below the preindustrial level may a glaciation occur within the next 10 ka. ... Given the continued anthropogenic CO₂ emissions, glacial inception is very unlikely to occur in the next 50 ka, because the timescale for CO₂ and temperature reduction toward unperturbed values in the absence of active removal is very long [IPCC, 2013], and only weak precessional forcing occurs in the next two precessional cycles." (A precessional cycle is around 21,000 years, the time it takes for the perihelion to move all the way around the tropical year.)

As the NAS report indicates, scientific knowledge regarding climate change was more uncertain than it is today. At the time that Rasool and Schneider wrote their 1971 paper, climatologists had not yet recognized the significance of greenhouse gases other than water vapor and carbon dioxide, such as methane, nitrous oxide, and chlorofluorocarbons. Early in that decade, carbon dioxide was the only widely studied human-influenced greenhouse gas. The attention drawn to atmospheric gases in the 1970s stimulated many discoveries in subsequent decades. As the temperature pattern changed, global cooling was of waning interest by 1979.

The ice age fallacy

A common argument used to dismiss the significance of human-caused climate change is to allege that scientists showed concerns about global cooling which did not materialise, and there is therefore no need to heed current scientific concerns about global warming. In a 1998 article promoting the Oregon Petition, Fred Singer argued that expert concerns about global warming should be dismissed on the basis that what he called "the same hysterical fears" had supposedly been expressed earlier about global cooling.

Bryan Walsh of Time magazine (2013) calls this argument "the Ice Age Fallacy". Illustrating the argument, for several years an image had been circulated of a Time cover, supposedly dated 1977, showing a penguin above a cover story title "How to Survive the Coming Ice Age". In March 2013, The Mail on Sunday published an article by David Rose, showing this same cover image, to support his claim that there was as much concern in the 1970s about a "looming 'ice age'" as there was now about global warming. After researching the authenticity of the magazine cover image, in July 2013, Walsh confirmed that the image was a hoax, modified from a 2007 cover story image for "The Global Warming Survival Guide".

Year Without a Summer

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Year_Without_a_Summer 

 

Year Without a Summer
1816 summer temperature anomaly compared with average temperatures from 1971 to 2000
Volcano	Mount Tambora
Start date	Eruption occurred on 10 April 1815
Type	Ultra-Plinian
Location	Lesser Sunda Islands, Dutch East Indies (now Republic of Indonesia)
Impact	Caused a volcanic winter that dropped temperatures by 0.4–0.7°C (or 0.7–1°F) worldwide

The year 1816 AD is known as the Year Without a Summer because of severe climate abnormalities that caused average global temperatures to decrease by 0.4–0.7 °C (0.7–1 °F). Summer temperatures in Europe were the coldest of any on record between 1766 and 2000, resulting in crop failures and major food shortages across the Northern Hemisphere.

Evidence suggests that the anomaly was predominantly a volcanic winter event caused by the massive 1815 eruption of Mount Tambora in April in the Dutch East Indies (modern-day Indonesia). This eruption was the largest in at least 1,300 years (after the hypothesized eruption causing the volcanic winter of 536); its effect on the climate may have been exacerbated by the 1814 eruption of Mayon in the Philippines.

Description

The Year Without a Summer was an agricultural disaster; historian John D. Post called it "the last great subsistence crisis in the Western world". The climatic aberrations of 1816 had their greatest effect on New England, Atlantic Canada, and Western Europe.

The main cause of the Year Without a Summer is generally held to be a volcanic winter created by the April 1815 eruption of Mount Tambora on Sumbawa. The eruption had a volcanic explosivity index (VEI) ranking of 7, and ejected at least 37 km³ (8.9 cu mi) of dense-rock equivalent material into the atmosphere. It remains the most recent confirmed VEI-7 eruption to date.

Other large volcanic eruptions (of at least VEI-4) around this time include:

• The 1808 mystery eruption in the southwestern Pacific Ocean
• 1812, La Soufrière on Saint Vincent in the Caribbean
• 1812, Awu in the Sangihe Islands, Dutch East Indies
• 1813, Suwanosejima in the Ryukyu Islands
• 1814, Mayon in the Philippines

These eruptions had built up a substantial amount of atmospheric dust, and thus temperatures fell worldwide as the airborne material blocked sunlight in the stratosphere. According to a 2012 analysis by Berkeley Earth, the 1815 Tambora eruption caused a temporary drop in the Earth's average land temperature of about one degree Celsius; smaller temperature drops were recorded from the 1812–1814 eruptions.

The Earth had already been in a centuries-long period of cooling that began in the 14th century. Known today as the Little Ice Age, it had already caused considerable agricultural distress in Europe. The eruption of Tambora occurred near the end of the Little Ice Age, exacerbating the background global cooling of the period.

This period also occurred during the Dalton Minimum, a period of relatively low solar activity from 1790 to 1830. May 1816 had the lowest Wolf number (0.1) to date since records on solar activity began. It is not yet known, however, if and how changes in solar activity affect Earth's climate, and this correlation does not prove that lower solar activity produces global cooling.

Africa

No direct evidence for conditions in the Sahel region have been found, though conditions from surrounding areas have implied above-normal rainfall. Below the Sahel, the coastal regions of West Africa likely experienced below-normal levels of precipitation. Severe storms affected the South African coast during the Southern Hemisphere winter. On July 29–30, 1816, a violent storm occurred near Cape Town, which brought forceful northerly winds and hail and caused severe damage to shipping.

Asia

The monsoon season in China was disrupted, resulting in overwhelming floods in the Yangtze Valley. Fort Shuangcheng reported fields disrupted by frost and conscripts deserting as a result. Summer snowfall or otherwise mixed precipitation was reported in various locations in Jiangxi and Anhui. In Taiwan, snow was reported in Hsinchu and Miaoli, and frost was reported in Changhua. A large-scale famine in Yunnan helped reverse the fortunes of the ruling Qing dynasty.

In India, the delayed summer monsoon caused late torrential rains that aggravated the spread of cholera from a region near the Ganges in Bengal to as far as Moscow. In Bengal, abnormal cold and snow was reported in the winter monsoon.

In Japan, which was still cautious after the cold-weather-related Great Tenmei famine of 1782–1788, cold damaged crops, but no crop failures were reported and there was no adverse effect on population.

Sulfate concentration in ice cores from Greenland. An unknown eruption occurred before 1810. The peak after 1815 was caused by Mount Tambora.

Europe

As a result of the series of volcanic eruptions in the 1810s, crops had been poor for several years; the final blow came in 1815 with the eruption of Tambora. Europe, still recuperating from the Napoleonic Wars, suffered from widespread food shortages, resulting in its worst famine of the century. Low temperatures and heavy rains resulted in failed harvests in Great Britain and Ireland. Famine was prevalent in north and southwest Ireland, following the failure of wheat, oat, and potato harvests. Food prices rose sharply throughout Europe. With the cause of the problems unknown, hungry people demonstrated in front of grain markets and bakeries. Food riots took place in many European cities. Though riots were common during times of hunger, the food riots of 1816 and 1817 were the most violent period on the continent since the French Revolution.

Between 1816 and 1819, major typhus epidemics occurred in parts of Europe, including Ireland, Italy, Switzerland, and Scotland, precipitated by the famine. More than 65,000 people died as the disease spread out of Ireland.

The long-running Central England temperature record reported the eleventh coldest year on record since 1659, as well as the third coldest summer and the coldest July on record. Widespread flooding of Europe's major rivers is attributed to the event, as is frost in August. Hungary experienced snowfall colored brown by volcanic ash; in northern Italy, red snow fell throughout the year.

In western Switzerland, the summers of 1816 and 1817 were so cold that an ice dam formed below a tongue of the Giétro Glacier in the Val de Bagnes, creating a lake. Despite engineer Ignaz Venetz's efforts to drain the growing lake, the ice dam collapsed catastrophically in June 1818, killing forty people in the resulting flood.

North America

In the spring and summer of 1816, a persistent "dry fog" was observed in parts of the eastern United States. The fog reddened and dimmed sunlight such that sunspots were visible to the naked eye. Neither wind nor rainfall dispersed the "fog", retrospectively characterized by Clive Oppenheimer as a "stratospheric sulfate aerosol veil".

The weather was not in itself a hardship for those accustomed to long winters. Hardship came from the weather's effect on crops and thus on the supply of food and firewood. The consequences were felt most strongly at higher elevations, where farming was already difficult even in good years. In May 1816, frost killed off most crops in the higher elevations of Massachusetts, New Hampshire, Vermont, and upstate New York. On June 6, snow fell in Albany, New York, and Dennysville, Maine. In Cape May, New Jersey, frost was reported five nights in a row in late June, causing extensive crop damage. Though fruit and vegetable crops survived in New England, corn was reported to have ripened so poorly that no more than a quarter of it was usable for food, and much of it was moldy and not even fit for animal feed. The crop failures in New England, Canada, and parts of Europe caused food prices to rise sharply. In Canada, Quebec ran out of bread and milk, and Nova Scotians found themselves boiling foraged herbs for sustenance.

Sarah Snell Bryant, of Cummington, Massachusetts, wrote in her diary: "Weather backward." At the Church Family of Shakers near New Lebanon, New York, Nicholas Bennet wrote in May 1816 that "all was froze" and the hills were "barren like winter". Temperatures fell below freezing almost every day in May. The ground froze on June 9; on June 12, the Shakers had to replant crops destroyed by the cold. On July 7, it was so cold that all of their crops had stopped growing. Salem, Massachusetts physician Edward Holyoke - a weather observer and amateur astronomer - while in Franconia, New Hampshire, wrote on June 7, "exceedingly cold. Ground frozen hard, and squalls of snow through the day. Icicles 12 inches long in the shade of noon day." After a lull, by August 17, Holyoke noted an abrupt change from summer to winter by August 21, when a meager bean and corn crop were killed. "The fields," he wrote, "were as empty and white as October." The Berkshires saw frost again on August 23, as did much of New England and upstate New York.

Massachusetts historian William G. Atkins summed up the disaster:

Severe frosts occurred every month; June 7th and 8th snow fell, and it was so cold that crops were cut down, even freezing the roots ... In the early Autumn when corn was in the milk [the endosperm inside the kernel was still liquid] it was so thoroughly frozen that it never ripened and was scarcely worth harvesting. Breadstuffs were scarce and prices high and the poorer class of people were often in straits for want of food. It must be remembered that the granaries of the great west had not then been opened to us by railroad communication, and people were obliged to rely upon their own resources or upon others in their immediate locality.

In July and August, lake and river ice was observed as far south as northwestern Pennsylvania. Frost was reported in Virginia on August 20 and 21. Rapid, dramatic temperature swings were common, with temperatures sometimes reverting from normal or above-normal summer temperatures as high as 95 °F (35 °C) to near-freezing within hours. Thomas Jefferson, by then retired from politics to his estate at Monticello, sustained crop failures that sent him further into debt. On September 13, a Virginia newspaper reported that corn crops would be one half to two-thirds short and lamented that "the cold as well as the drought has nipt the buds of hope". A Norfolk, Virginia, newspaper reported:

It is now the middle of July, and we have not yet had what could properly be called summer. Easterly winds have prevailed for nearly three months past ... the sun during that time has generally been obscured and the sky overcast with clouds; the air has been damp and uncomfortable, and frequently so chilling as to render the fireside a desirable retreat.

Regional farmers succeeded in bringing some crops to maturity, but corn and other grain prices rose dramatically. The price of oats, for example, rose from 12¢ per bushel in 1815 to 92¢ per bushel in 1816. Crop failures were aggravated by inadequate transportation infrastructure; with few roads or navigable inland waterways and no railroads, it was prohibitively expensive to import food in most of the country.

Maryland experienced brown, bluish, and yellow snowfall in April and May, colored by volcanic ash in the atmosphere.

South America

A newspaper account of northeastern Brazil was published in the United Kingdom:

By an arrival at Liverpool we have received accounts from Pernambuco of the 8th of Feb. [1817], which state that a most uncommon drought has been experienced in the tropical regions of the Brazils, or that part of the country between Pernambuco and Rio Janiero. By this circumstance all the streams had been dried up, the cattle were dying or dead, and all the population emigrating to the borders of the great rivers in search of water. The greatest distress prevailed, provisions were wanting, and the mills completely at a stand. They have no windmills, so that no corn could be ground. Vessels have been sent from Pernambuco to the United States to fetch flour, and what had tended to increase this distress was the interruption of the coasting trade through the dread of war with Buenos Ayres.

Societal effects

Caspar David Friedrich paintings before and after the eruption

The Monk by the Sea (ca. 1808–1810)

 

Two Men by the Sea (1817)

High levels of tephra in the atmosphere caused a haze to hang over the sky for several years after the eruption, and created rich red hues in sunsets. Paintings during the years before and after seem to confirm that these striking reds were not present before Mount Tambora's eruption, and depict moodier, darker scenes, even in the light of both the sun and the moon. Caspar David Friedrich's The Monk by the Sea (ca. 1808–1810) and Two Men by the Sea (1817) indicate this shift of mood.

Chichester Canal (1828) by J. M. W. Turner

A 2007 study analyzing paintings created between the years 1500 and 1900 around the times of notable volcanic events found a correlation between volcanic activity and the amount of red used in the painting. High levels of tephra in the atmosphere led to spectacular sunsets during this period, as depicted in the paintings of J. M. W. Turner, and may have given rise to the yellow tinge predominant in his paintings such as Chichester Canal (1828). Similar phenomena were observed after the 1883 eruption of Krakatoa, and on the West Coast of the United States following the 1991 eruption of Mount Pinatubo.

The lack of oats to feed horses may have inspired the German inventor Karl Drais to research new ways of horseless transportation, which led to the invention of the draisine and velocipede, a precursor of the bicycle.

The crop failures of the "Year without a Summer" may have shaped the settlement of the Midwestern United States, as many thousands of people left New England for western New York and the Northwest Territory in search of a more hospitable climate, richer soil, and better growing conditions. Indiana became a state in December 1816, and Illinois did two years later. British historian Lawrence Goldman has suggested that migration into the burned-over district of upstate New York was responsible for centering the abolitionist movement in that region.

According to historian L. D. Stillwell, Vermont alone experienced a decrease in population of between 10,000 and 15,000 in 1816 and 1817, erasing seven previous years of population growth. Among those who left Vermont were the family of Joseph Smith, who moved from Norwich, Vermont, to Palmyra, New York. This move precipitated the series of events that culminated in Smith founding the Church of Jesus Christ of Latter-day Saints.

In June 1816, "incessant rainfall" during the "wet, ungenial summer" forced Mary Shelley, Percy Bysshe Shelley, Lord Byron, John William Polidori, and their friends to stay indoors at Villa Diodati for much of their Swiss holiday. Inspired by a collection of German ghost stories that they had read, Lord Byron proposed a contest to see who could write the scariest story, leading Shelley to write Frankenstein and Lord Byron to write "A Fragment", which Polidori later used as inspiration for The Vampyre – a precursor to Dracula. These days inside Villa Diodati, remembered fondly by Mary Shelley, were occupied by opium use and intellectual conversations. After listening intently to one of these conversations, she awoke with the image of Victor Frankenstein kneeling over his monstrous creation, and thus was inspired to write Frankenstein. Lord Byron was inspired to write the poem "Darkness" by a single day when "the fowls all went to roost at noon and candles had to be lit as at midnight". The imagery in the poem is starkly similar to the conditions of the Year Without a Summer:

I had a dream, which was not all a dream.
The bright sun was extinguish'd, and the stars
Did wander darkling in the eternal space,
Rayless, and pathless, and the icy earth
Swung blind and blackening in the moonless air;
Morn came and went—and came, and brought no day

Justus von Liebig, a chemist who had experienced the famine as a child in Darmstadt, later studied plant nutrition and introduced mineral fertilizers.

Comparable events

Toba catastrophe

The 1628–1626 BC climate disturbances, usually attributed to the Minoan eruption of Santorini

The Hekla 3 eruption of about 1200 BC, contemporary with the historical Bronze Age collapse

The Hatepe eruption (sometimes referred to as the Taupō eruption), around AD 180

The winter of 536 has been linked to the effects of a volcanic eruption, possibly at Krakatoa, or of Ilopango in El Salvador

The Heaven Lake eruption of Paektu Mountain between modern-day North Korea and the People's Republic of China, in 969 (± 20 years), is thought to have had a role in the downfall of Balhae

The 1257 Samalas eruption of Mount Rinjani on the island of Lombok in 1257

The 1452/1453 mystery eruption has been implicated in events surrounding the Fall of Constantinople in 1453

An eruption of Huaynaputina, in Peru, caused 1601 to be the coldest year in the Northern Hemisphere for six centuries (see Russian famine of 1601–1603); 1601 consisted of a bitterly cold winter, a cold, frosty, nonexistent spring, and a cool, cloudy, wet summer

An eruption of Laki, in Iceland, was responsible for up to hundreds of thousands of fatalities throughout the Northern Hemisphere (over 25,000 in England alone), and one of the coldest winters ever recorded in North America, 1783–1784; long-term consequences included poverty and famine that may have contributed to the French Revolution in 1789.

The 1883 eruption of Krakatoa caused average Northern Hemisphere summer temperatures to fall by as much as 1.2 °C (2.2 °F). One of the wettest rainy seasons in recorded history followed in California during 1883–1884.

The eruption of Mount Pinatubo in 1991 led to odd weather patterns and temporary cooling in the United States, particularly in the Midwest and parts of the Northeast. Every month in 1992 except for January and February was colder than normal. More rain than normal fell across the West Coast of the United States, particularly California, during the 1991–1992 and 1992–1993 rainy seasons. The American Midwest experienced more rain and major flooding during the spring and summer of 1993. This may also have contributed to the historic "Storm of the Century" on the Atlantic Coast in March that same year.