Wei-Hock "Willie" Soon (born 1966) is a Malaysian astrophysicist and aerospace engineer employed as a part-time researcher at the Solar and Stellar Physics (SSP) Division of the Harvard-Smithsonian Center for Astrophysics.
Soon co-authored The Maunder Minimum and the Variable Sun–Earth Connection with Steven H. Yaskell. The book treats historical and proxy records of climate change coinciding with the Maunder Minimum, a period from 1645 to about 1715 when sunspots became exceedingly rare.
From 2005 to 2015, Soon had received over $1.2 million from the
fossil fuel industry, while failing to disclose that conflict of
interest in most of his work.
Early life and education
Willie Soon was born in Kangar, Malaysia, in 1966. He attended Khoon Aik Primary School in Kangar, Perlis, then Sekolah Menengah Syed Sirajudin Secondary School in Jejawi, Perlis, and Sekolah Menengah Dato Sheikh Ahmad Secondary School in Arau, Perlis. To further his education he emigrated to the United States in 1980 and attended the University of Southern California, receiving a B.Sc. in 1985, followed by a M.Sc. in 1987 and then a Ph.D. in Aerospace Engineering [with distinction] in 1991. His doctoral thesis was titled Non-equilibrium kinetics in high-temperature gases. He received the IEEE Nuclear and Plasma Sciences Society Graduate Scholastic Award in 1989 and the Rockwell Dennis Hunt Scholastic Award from the University of Southern California in 1991.
In 2003, Willie Soon was first author on a review paper in the journal Climate Research, with Sallie Baliunas
as co-author. This paper concluded that "the 20th century is probably
not the warmest nor a uniquely extreme climatic period of the last
millennium."
Shortly thereafter, 13 scientists published a refutation of the paper.
They raised three main objections: (1) Soon and Baliunas used data
reflective of changes in moisture, rather than temperature; (2) they
failed to distinguish between regional and hemispheric mean temperature
anomalies; and (3) they reconstructed past temperatures from proxy
evidence not capable of resolving decadal trends. Soon, Baliunas and David Legates published a response to these objections.
After disagreement with the publisher and with other members of the editorial board, Hans von Storch,
Clare Goodess, and two more members of the journal's ten-member
editorial board resigned in protest against what they felt was a failure
of the peer review process on the part of the journal. Otto Kinne, managing director of the journal's parent company, eventually stated that "CR [Climate Research]
should have been more careful and insisted on solid evidence and
cautious formulations before publication" and that "CR should have
requested appropriate revisions of the manuscript prior to publication."
Soon and Baliunas have also been criticised because they did not disclose that their research budget was funded in part by the American Petroleum Institute.
2011: Funding controversy
In 2011, it was revealed that Soon received over $1 million from petroleum and coal interests since 2001. Harvard–Smithsonian Center for Astrophysics documents obtained by Greenpeace under the US Freedom of Information Act show that the Charles G. Koch Charitable Foundation
gave Soon two grants totaling $175,000 in 2005–06 and again in 2010.
Multiple grants from the American Petroleum Institute between 2001 and
2007 totalled $274,000, and grants from Exxon Mobil
totalled $335,000 between 2005 and 2010. Other coal and oil industry
sources which funded him include the Mobil Foundation, the Texaco
Foundation and the Electric Power Research Institute.
Soon has stated unequivocally that he has "never been motivated by
financial reward in any of my scientific research" and "would have
accepted money from Greenpeace if they had offered it to do my
research."
Putting forward health reasons, in 2011 Soon went from full-time employment by the Smithsonian at the Harvard–Smithsonian Center for Astrophysics
to a part-time position. The Center's spokesman said "Willie's opinions
regarding climate change are his personal views not shared within our
research organization". Its former director Irwin Shapiro
said no attempt had been made to suppress Soon's views, and there had
been no complaints from other scientists there: "As far as I can tell,
no one pays any attention to him." Soon has been defended by others
agreeing with his views. In 2013, theoretical physicist Freeman Dyson wrote in an email to The Boston Globe:
"The whole point of science is to question accepted dogmas. For that
reason, I respect Willie Soon as a good scientist and a courageous
citizen." Republican Senator Jim Inhofe has cited Soon, and Inhofe's former director of communications Marc Morano
said that "Willie Soon is a hero of the skeptical movement. When you
are an early pioneer, you are going to face the scrutiny and attacks."
Soon has links with conservative groups which promote his writings to
influence the public debate on climate change, including The Heartland Institute, and the Committee for a Constructive Tomorrow. In a speech at The Heritage Foundation, he accused the IPCC of being "a pure bully" engaged in "blatant manipulations of fact", and said "Stop politicizing science! Just stop!"
January 2015 Monckton et al. paper
With William M. Briggs, geography professor David Legates, and journalist and British politician Christopher Monckton, Soon co-authored a paper published by the Chinese Science Bulletin in 2015. Climatologist Gavin Schmidt
described the paper as "complete trash". He said that the model used is
not new, "they arbitrarily restrict its parameters and then declare all
other models wrong."
2015: Disclosure violations
Soon, as a researcher at the Harvard-Smithsonian Center for Astrophysics (CfA), is a part-time employee of the Smithsonian Institution, a government agency covered by the Freedom of Information Act (FOIA). Greenpeace
worker Kert Davies made a succession of FOIA requests for Soon's
correspondence and grant arrangements and in 2014 was given documents
disclosing arrangements both Soon and the CfA had with funders. Later in
2014, Davies left Greenpeace to become executive director of a newly
founded non-profit, Climate Investigations Center.
The Smithsonian does not fund Soon, who "pursues external grants to fund his research." This funding had exceeded US$1.5 million since 2001;
under standard CfA procedures, more than half of the $1.2 million
funding since 2005 had gone towards the Smithsonian's facility operating
costs, with the remainder being passed on to Soon as his salary. Other
researchers there have a similar arrangement, but nearly all of their
funding comes through peer-reviewed award processes from government
bodies such as NASA and the National Science Foundation, whereas Soon has received very little federal money.
Soon's funding is highly unusual at the Smithsonian in its association
with private interests. It included at least $230,000 from the Charles G. Koch Foundation which is associated with the oil industry and $469,560 from the Southern Company which uses coal to generate electricity. Exxon Mobil and the American Petroleum Institute also provided funding, which was later replaced by anonymous donors through the Donors Trust, a donor-advised fund that offers anonymity to clients who do not wish to make their donations public. The latter was identified by a 2013 Drexel University study as the largest single provider of money to political efforts to fight climate-change policy.
A 2008 contract agreed to by the CfA required the institute to notify
the Southern Company before disclosing that Southern had provided
funding, and both the CfA and Willie Soon to provide Southern with
advance copies of any publications "for comment and input", though the
company could not block publications or require changes.
The Chinese Science Bulletin
has a strict policy requiring disclosure of "all relationships or
interests that could influence or bias the work", including
"professional interests or personal beliefs that may influence your
research", for example previous receipt of research grants. The Monckton
et al. paper published in January 2015 included a statement by the
authors, including Soon, that they had no conflict of interest, and
Davies wrote to the journal about the undisclosed funding shown by the
documents. On 24 January the journal replied that they would "look into
the matter as appropriate". The story was published by The Boston Globe
on 26 January with a statement by Monckton that allegations of failure
to disclose a material conflict of interest were untrue, as the authors
had not "received any funding whatsoever for our research, which was
conducted in our own time". He said that the Heartland Institute had provided funding to make the paper available to the public on the journal's website.
On February 21, publications including The Guardian and The New York Times
reported that Soon had failed to disclose conflicts of interest in at
least 11 papers since 2008, and alleged that Soon had violated ethical
guidelines of at least eight of those journals publishing his work. Charles R. Alcock,
director of the Harvard-Smithsonian Center for Astrophysics, described
the disclosure violations as "inappropriate behavior" that they would
"have to handle with Dr. Soon internally". On the same day, Nature
reported that the CfA had launched an investigation into whether Soon
had properly reported the funding arrangements shown in the documents.
Alcock said "We want to get the facts straight. If there is evidence of
failure to disclose, yes, we have a problem."
He said that the contract with Southern preventing disclosure of their
funding "was a mistake", and in a later email reply to questions said
"We will not permit similar wording in future grant agreements".
The Smithsonian announced that its Inspector General would investigate,
and in addition there was to be a full review of the Smithsonian's
ethics and disclosure policies about sponsored research, led by former NSF director Rita R. Colwell.
On March 2, 2015, The Heartland Institute conservative think tank released a statement by Soon,
which said he had "been the target of attacks in the press by various
radical environmental and politically motivated groups". He described
this as "a shameless attempt to silence my scientific research and
writings, and to make an example out of me as a warning to any other
researcher who may dare question in the slightest their fervently held
orthodoxy of anthropogenic global warming."
Some of the journals that had published Soon's work had begun reviewing
the papers in relation to their policies requiring disclosure: Soon
said he had "always complied with what I understood to be disclosure
practices in my field generally". He would be "happy to comply" if they
required further disclosure, and "would ask only that other authors—on
all sides of the debate—are also required to make similar disclosures."
He also requested that journalists who had reported on his actions similarly examined disclosure by other scientists. An investigation by InsideClimate News
could find no cases where mainstream climatologists had failed to
disclose the funding of their research. Unlike Soon, who had approached
private funders directly, their funding was almost entirely obtained
through open competitive peer-reviewed applications to public bodies.
Climate scientist Andrew Dessler
said "People always acknowledge their grants, and that's not really an
issue". Though it was almost certain that a disclosure issue could
arise, intentionally or otherwise, no instances were known. The nearest
case was raised by Steven Milloy's "Junk Science" blog when Nature Climate Change published a 2012 study by Kerry Emanuel,
who was paid a fixed amount by two companies to sit on their board.
Although the companies did not fund his research, the journal then added
disclosure of these board memberships. The blog raised the same concern
about a paper published a year later, but Proceedings of the National Academy of Sciences decided this disclosure was not required.
In April 2015, a Southern Company spokesman said "Our agreement
with the Smithsonian Astrophysical Observatory expires later this year
and there are no plans to renew it". It still required Soon to produce a
study on "Solar Activity Variation on Multiple Timescales" by November
2015.
Accumulation in the atmosphere of greenhouse gases, especially those resulting from humans burning fossil fuels, has been found to be the predominant cause of global warming and climate change.
Attribution of recent climate change is the effort to scientifically ascertain mechanisms responsible for recent global warming and related climate changes on Earth. The effort has focused on changes observed during the period of instrumental temperature record, particularly in the last 50 years. This is the period when human activity has grown fastest and observations of the atmosphere above the surface have become available. According to the Intergovernmental Panel on Climate Change (IPCC), it is "extremely likely" that human influence was the dominant cause of global warming between 1951 and 2010. The best estimate is that observed warming since 1951 has been entirely human caused.
Some of the main human activities that contribute to global warming are:
Multiple lines of evidence support attribution of recent climate change to human activities:
A physical understanding of the climate system: greenhouse gas concentrations have increased and their warming properties are well-established.
Historical estimates of past climate changes suggest that the recent changes in global surface temperature are unusual.
Computer-based climate models are unable to replicate the observed warming unless human greenhouse gas emissions are included.
Natural forces alone (such as solar and volcanic activity) cannot explain the observed warming.
The IPCC's attribution of recent global warming to human activities is a view shared by the scientific community, and is also supported by 196 other scientific organizations worldwide.
Background
The Keeling Curve shows the long-term increase of atmospheric carbon dioxide (CO 2) concentrations from 1958–2018. Monthly CO 2 measurements display seasonal oscillations in an upward trend. Each year's maximum occurs during the Northern Hemisphere's late spring.
Factors affecting Earth's climate can be broken down into feedbacks and forcings. A forcing is something that is imposed externally on the climate system. External forcings include natural phenomena such as volcanic eruptions and variations in the sun's output. Human activities can also impose forcings, for example, through changing the composition of the atmosphere.
Radiative forcing is a measure of how various factors alter the energy balance of the Earth's atmosphere.
A positive radiative forcing will tend to increase the energy of the
Earth-atmosphere system, leading to a warming of the system. Between the
start of the Industrial Revolution in 1750, and the year 2005, the increase in the atmospheric concentration of carbon dioxide (chemical formula: CO 2) led to a positive radiative forcing, averaged over the Earth's surface area, of about 1.66 watts per square metre (abbreviated W m−2).
Climate feedbacks can either amplify or dampen the response of the climate to a given forcing.
There are many feedback mechanisms in the climate system that can either amplify (a positive feedback) or diminish (a negative feedback) the effects of a change in climate forcing.
The climate system will vary in response to changes in forcings.
The climate system will show internal variability both in the presence
and absence of forcings imposed on it, (see images opposite). This
internal variability is a result of complex interactions between
components of the climate system, such as the coupling between the atmosphere and ocean (see also the later section on Internal climate variability and global warming). An example of internal variability is the El Niño–Southern Oscillation.
Detection vs. attribution
Probability density function (PDF) of fraction of surface temperature trends since 1950 attributable to human activity, based on IPCC AR5 10.5
In detection and attribution, the natural factors considered usually include changes in the Sun's output and volcanic eruptions, as well as natural modes of variability such as El Niño and La Niña. Human factors include the emissions of heat-trapping "greenhouse" gases and particulates as well as clearing of forests and other land-use changes. Figure source: NOAA NCDC.
Detection and attribution of climate signals, as well as its
common-sense meaning, has a more precise definition within the climate
change literature, as expressed by the IPCC. Detection of a climate signal does not always imply significant attribution. The IPCC's Fourth Assessment Report says "it is extremely likely
that human activities have exerted a substantial net warming influence
on climate since 1750," where "extremely likely" indicates a probability
greater than 95%. Detection of a signal requires demonstrating that an observed change is statistically significantly different from that which can be explained by natural internal variability
.
Attribution requires demonstrating that a signal is:
unlikely to be due entirely to internal variability;
consistent with the estimated responses to the given combination of anthropogenic and natural forcing
not consistent with alternative, physically plausible explanations
of recent climate change that exclude important elements of the given
combination of forcings.
Key attributions
Greenhouse gases
Carbon dioxide is the primary greenhouse gas that is contributing to recent climate change. CO 2 is absorbed and emitted naturally as part of the carbon cycle, through animal and plant respiration, volcanic eruptions, and ocean-atmosphere exchange.
Human activities, such as the burning of fossil fuels and changes in
land use (see below), release large amounts of carbon to the atmosphere,
causing CO 2 concentrations in the atmosphere to rise.
The high-accuracy measurements of atmospheric CO 2 concentration, initiated by Charles David Keeling in 1958, constitute the master time series documenting the changing composition of the atmosphere.
These data have iconic status in climate change science as evidence of
the effect of human activities on the chemical composition of the global
atmosphere.
In May 2019 the concentration of CO2 in the atmosphere reached
415 PPM. The last time when it reached this level was 2.6 - 5.3 million
years ago. Without human intervention, it would be 280 PPM
Emission Database for Global Atmospheric Research version 4.2, fast track 2010 project
Water vapor is the most abundant greenhouse gas and is the largest
contributor to the natural greenhouse effect, despite having a short
atmospheric lifetime (about 10 days).
Some human activities can influence local water vapor levels. However,
on a global scale, the concentration of water vapor is controlled by
temperature, which influences overall rates of evaporation and precipitation. Therefore, the global concentration of water vapor is not substantially affected by direct human emissions.
Land use
Climate change is attributed to land use for two main reasons. Between 1750 and 2007, about two-thirds of anthropogenic CO 2 emissions were produced from burning fossil fuels, and about one-third of emissions from changes in land use, primarily deforestation.
Deforestation both reduces the amount of carbon dioxide absorbed by
deforested regions and releases greenhouse gases directly, together with
aerosols, through biomass burning that frequently accompanies it.
Some of the causes of climate change are, generally, not
connected with it directly in the media coverage. For example, the harm
done by humans to the populations of Elephants and Monkeys contributes to deforestation therefore to climate change.
A second reason that climate change has been attributed to land use is that the terrestrial albedo is often altered by use, which leads to radiative forcing. This effect is more significant locally than globally.
Livestock and land use
Worldwide, livestock production occupies 70% of all land used for agriculture, or 30% of the ice-free land surface of the Earth.
More than 18% of anthropogenic greenhouse gas emissions are attributed
to livestock and livestock-related activities such as deforestation and
increasingly fuel-intensive farming practices. Specific attributions to the livestock sector include:
With virtual certainty, scientific consensus has attributed various forms of climate change, chiefly cooling effects, to aerosols, which are small particles or droplets suspended in the atmosphere.
Key sources to which anthropogenic aerosols are attributed include:
One global climate model's
reconstruction of temperature change during the 20th century as the
result of five studied forcing factors and the amount of temperature
change attributed to each.
Over the past 150 years human activities have released increasing quantities of greenhouse gases into the atmosphere. This has led to increases in mean global temperature, or global warming. Other human effects are relevant—for example, sulphate aerosols are believed to have a cooling effect. Natural factors also contribute. According to the historical temperature record of the last century, the Earth's near-surface air temperature has risen around 0.74 ± 0.18 °Celsius (1.3 ± 0.32 °Fahrenheit).
A historically important question in climate change research has regarded the relative importance of human activity and non-anthropogenic causes during the period of instrumental record. In the 1995 Second Assessment Report (SAR), the IPCC
made the widely quoted statement that "The balance of evidence suggests
a discernible human influence on global climate". The phrase "balance
of evidence" suggested the (English) common-law standard of proof
required in civil as opposed to criminal courts: not as high as "beyond
reasonable doubt". In 2001 the Third Assessment Report
(TAR) refined this, saying "There is new and stronger evidence that
most of the warming observed over the last 50 years is attributable to
human activities". The 2007 Fourth Assessment Report (AR4) strengthened this finding:
"Anthropogenic warming of the climate system is widespread and
can be detected in temperature observations taken at the surface, in the
free atmosphere and in the oceans. Evidence of the effect of external
influences, both anthropogenic and natural, on the climate system has
continued to accumulate since the TAR."
Other findings of the IPCC Fourth Assessment Report include:
that it is due to known natural external causes alone. The warming
occurred in both the ocean and the atmosphere and took place at a time
when natural external forcing factors would likely have produced
cooling."
"From new estimates of the combined anthropogenic forcing due to greenhouse gases, aerosols, and land surface changes, it is extremely likely (>95%) that human activities have exerted a substantial net warming influence on climate since 1750."
Over the past five decades there has been a global warming of approximately 0.65 °C (1.17 °F) at the Earth's surface (see historical temperature record).
Among the possible factors that could produce changes in global mean
temperature are internal variability of the climate system, external
forcing, an increase in concentration of greenhouse gases, or any
combination of these. Current studies indicate that the increase in
greenhouse gases, most notably CO 2, is mostly responsible for the observed warming. Evidence for this conclusion includes:
Estimates of internal variability from climate models, and
reconstructions of past temperatures, indicate that the warming is
unlikely to be entirely natural.
Climate models forced by natural factors and increased
greenhouse gases and aerosols reproduce the observed global temperature
changes; those forced by natural factors alone do not.
"Fingerprint" methods (see below) indicate that the pattern of change is closer to that expected from greenhouse gas-forced change than from natural change.
The plateau in warming from the 1940s to 1960s can be attributed largely to sulphate aerosol cooling.
Details on attribution
For
Northern Hemisphere temperature, recent decades appear to be the
warmest since at least about 1000AD, and the warming since the late 19th
century is unprecedented over the last 1000 years. Older data are insufficient to provide reliable hemispheric temperature estimates.
Recent scientific assessments find that most of the warming of the
Earth's surface over the past 50 years has been caused by human
activities.
This conclusion rests on multiple lines of evidence. Like the warming
"signal" that has gradually emerged from the "noise" of natural climate
variability, the scientific evidence for a human influence on global
climate has accumulated over the past several decades, from many
hundreds of studies. No single study is a "smoking gun."
Nor has any single study or combination of studies undermined the large
body of evidence supporting the conclusion that human activity is the
primary driver of recent warming.
The first line of evidence is based on a physical understanding
of how greenhouse gases trap heat, how the climate system responds to
increases in greenhouse gases, and how other human and natural factors
influence climate. The second line of evidence is from indirect
estimates of climate changes over the last 1,000 to 2,000 years. These
records are obtained from living things and their remains (like tree rings and corals) and from physical quantities (like the ratio between lighter and heavier isotopes of oxygen in ice cores),
which change in measurable ways as climate changes. The lesson from
these data is that global surface temperatures over the last several
decades are clearly unusual, in that they were higher than at any time
during at least the past 400 years. For the Northern Hemisphere, the recent temperature rise is clearly unusual in at least the last 1,000 years (see graph opposite).
The third line of evidence is based on the broad, qualitative
consistency between observed changes in climate and the computer model
simulations of how climate would be expected to change in response to
human activities. For example, when climate models are run with
historical increases in greenhouse gases, they show gradual warming of
the Earth and ocean surface, increases in ocean heat content and the
temperature of the lower atmosphere, a rise in global sea level, retreat of sea ice and snow cover, cooling of the stratosphere, an increase in the amount of atmospheric water vapor, and changes in large-scale precipitation and pressure patterns. These and other aspects of modelled climate change are in agreement with observations.
"Fingerprint" studies
Reconstructions
of global temperature that include greenhouse gas increases and other
human influences (red line, based on many models) closely match measured
temperatures (dashed line). Those that only include natural influences (blue line, based on many models) show a slight cooling, which has not occurred.
The ability of models to generate reasonable histories of global
temperature is verified by their response to four 20th-century volcanic
eruptions: each eruption caused brief cooling that appeared in observed
as well as modeled records.
Finally, there is extensive statistical
evidence from so-called "fingerprint" studies. Each factor that affects
climate produces a unique pattern of climate response, much as each
person has a unique fingerprint. Fingerprint studies exploit these
unique signatures, and allow detailed comparisons of modelled and
observed climate change patterns. Scientists rely on such studies to
attribute observed changes in climate to a particular cause or set of
causes. In the real world, the climate changes that have occurred since
the start of the Industrial Revolution
are due to a complex mixture of human and natural causes. The
importance of each individual influence in this mixture changes over
time. Of course, there are not multiple Earths, which would allow an
experimenter to change one factor at a time on each Earth, thus helping
to isolate different fingerprints. Therefore, climate models are used to
study how individual factors affect climate. For example, a single
factor (like greenhouse gases) or a set of factors can be varied, and
the response of the modelled climate system to these individual or
combined changes can thus be studied.
Two
fingerprints of human activities on the climate are that land areas
will warm more than the oceans, and that high latitudes will warm more
than low latitudes. These projections have been confirmed by observations (shown above).
For example, when climate model simulations of the last century
include all of the major influences on climate, both human-induced and
natural, they can reproduce many important features of observed climate
change patterns. When human influences are removed from the model
experiments, results suggest that the surface of the Earth would
actually have cooled slightly over the last 50 years (see graph,
opposite). The clear message from fingerprint studies is that the
observed warming over the last half-century cannot be explained by
natural factors, and is instead caused primarily by human factors.
Another fingerprint of human effects on climate has been
identified by looking at a slice through the layers of the atmosphere,
and studying the pattern of temperature changes from the surface up
through the stratosphere (see the section on solar activity).
The earliest fingerprint work focused on changes in surface and
atmospheric temperature. Scientists then applied fingerprint methods to a
whole range of climate variables, identifying human-caused climate
signals in the heat content of the oceans, the height of the tropopause (the boundary between the troposphere and stratosphere, which has shifted upward by hundreds of feet in recent decades), the geographical patterns of precipitation, drought, surface pressure, and the runoff from major river basins.
Studies published after the appearance of the IPCC Fourth Assessment Report in 2007 have also found human fingerprints in the increased levels of atmospheric moisture (both close to the surface and over the full extent of the atmosphere), in the decline of Arctic sea ice extent, and in the patterns of changes in Arctic and Antarctic surface temperatures.
The message from this entire body of work is that the climate
system is telling a consistent story of increasingly dominant human
influence – the changes in temperature, ice extent, moisture, and circulation patterns fit together in a physically consistent way, like pieces in a complex puzzle.
Increasingly, this type of fingerprint work is shifting its
emphasis. As noted, clear and compelling scientific evidence supports
the case for a pronounced human influence on global climate. Much of the
recent attention is now on climate changes at continental and regional
scales, and on variables that can have large impacts on societies. For
example, scientists have established causal links between human
activities and the changes in snowpack, maximum and minimum (diurnal) temperature, and the seasonal timing of runoff over mountainous regions of the western United States. Human activity is likely to have made a substantial contribution to ocean surface temperature changes in hurricane
formation regions. Researchers are also looking beyond the physical
climate system, and are beginning to tie changes in the distribution and
seasonal behaviour of plant and animal species to human-caused changes
in temperature and precipitation.
For over a decade, one aspect of the climate change story seemed
to show a significant difference between models and observations. In the
tropics,
all models predicted that with a rise in greenhouse gases, the
troposphere would be expected to warm more rapidly than the surface.
Observations from weather balloons, satellites, and surface thermometers
seemed to show the opposite behaviour (more rapid warming of the
surface than the troposphere). This issue was a stumbling block in
understanding the causes of climate change. It is now largely resolved.
Research showed that there were large uncertainties in the satellite and weather balloon
data. When uncertainties in models and observations are properly
accounted for, newer observational data sets (with better treatment of
known problems) are in agreement with climate model results.
This
set of graphs shows the estimated contribution of various natural and
human factors to changes in global mean temperature between 1889–2006. Estimated contributions are based on multivariate analysis rather than model simulations.
The graphs show that human influence on climate has eclipsed the
magnitude of natural temperature changes over the past 120 years.
Natural influences on temperature—El Niño, solar variability, and
volcanic aerosols—have varied approximately plus and minus 0.2 °C
(0.4 °F), (averaging to about zero), while human influences have
contributed roughly 0.8 °C (1 °F) of warming since 1889.
Top chart: Observed global average temperature change (1870— ).Bottom chart: Data more recent than that plotted at left, and
merged for display on the same axis to emphasize relative strengths of
forces affecting temperature change. Human-caused forces have
increasingly dominated.
This does not mean, however, that all remaining differences between
models and observations have been resolved. The observed changes in some
climate variables, such as Arctic sea ice, some aspects of
precipitation, and patterns of surface pressure, appear to be proceeding
much more rapidly than models have projected. The reasons for these
differences are not well understood. Nevertheless, the bottom-line
conclusion from climate fingerprinting is that most of the observed
changes studied to date are consistent with each other, and are also
consistent with our scientific understanding of how the climate system
would be expected to respond to the increase in heat-trapping gases
resulting from human activities.
Extreme weather events
Frequency
of occurrence (vertical axis) of local June–July–August temperature
anomalies (relative to 1951–1980 mean) for Northern Hemisphere land in
units of local standard deviation (horizontal axis). According to Hansen et al. (2012),
the distribution of anomalies has shifted to the right as a consequence
of global warming, meaning that unusually hot summers have become more
common. This is analogous to the rolling of a dice: cool summers now
cover only half of one side of a six-sided die, white covers one side,
red covers four sides, and an extremely hot (red-brown) anomaly covers
half of one side.
One of the subjects discussed in the literature is whether or not
extreme weather events can be attributed to human activities.
Seneviratne et al. (2012)
stated that attributing individual extreme weather events to human
activities was challenging. They were, however, more confident over
attributing changes in long-term trends of extreme weather. For example,
Seneviratne et al. (2012)
concluded that human activities had likely led to a warming of extreme
daily minimum and maximum temperatures at the global scale.
Another way of viewing the problem is to consider the effects of
human-induced climate change on the probability of future extreme
weather events. Stott et al. (2003), for example, considered whether or not human activities had increased the risk of severe heat waves in Europe, like the one experienced in 2003. Their conclusion was that human activities had very likely more than doubled the risk of heat waves of this magnitude.
An analogy can be made between an athlete on steroids and human-induced climate change.
In the same way that an athlete's performance may increase from using
steroids, human-induced climate change increases the risk of some
extreme weather events.
Hansen et al. (2012)
suggested that human activities have greatly increased the risk of
summertime heat waves. According to their analysis, the land area of the
Earth affected by very hot summer temperature anomalies has greatly
increased over time. In the base period
1951-1980, these anomalies covered a few tenths of 1% of the global land
area. In recent years, this has increased to around 10% of the global land area. With high confidence, Hansen et al. (2012) attributed the 2010 Moscow and 2011 Texas heat waves to human-induced global warming.
An earlier study by Dole et al. (2011) concluded that the 2010 Moscow heatwave was mostly due to natural weather variability. While not directly citing Dole et al. (2011), Hansen et al. (2012) rejected this type of explanation. Hansen et al. (2012)
stated that a combination of natural weather variability and
human-induced global warming was responsible for the Moscow and Texas
heat waves.
Scientific literature and opinion
There are a number of examples of published and informal support for
the consensus view. As mentioned earlier, the IPCC has concluded that
most of the observed increase in globally averaged temperatures since
the mid-20th century is "very likely" due to human activities. The IPCC's conclusions are consistent with those of several reports produced by the US National Research Council.
A report published in 2009 by the U.S. Global Change Research Program concluded that "[global] warming is unequivocal and primarily human-induced."
A number of scientific organizations have issued statements that support the consensus view. Two examples include:
a joint statement made in 2005 by the national science academies of the G8, and Brazil, China and India;
The IPCC Fourth Assessment Report (2007), concluded that attribution
was possible for a number of observed changes in the climate.
However, attribution was found to be more difficult when assessing
changes over smaller regions (less than continental scale) and over
short time periods (less than 50 years).
Over larger regions, averaging reduces natural variability of the climate, making detection and attribution easier.
In 1996, in a paper in Nature titled "A search for human influences on the thermal structure of the atmosphere", Benjamin D. Santer
et al. wrote: "The observed spatial patterns of temperature change in
the free atmosphere from 1963 to 1987 are similar to those predicted by
state-of-the-art climate models incorporating various combinations of
changes in carbon dioxide, anthropogenic sulphate aerosol and
stratospheric ozone concentrations. The degree of pattern similarity
between models and observations increases through this period. It is
likely that this trend is partially due to human activities, although
many uncertainties remain, particularly relating to estimates of natural
variability."
A 2002 paper in the Journal of Geophysical Research
says "Our analysis suggests that the early twentieth century warming
can best be explained by a combination of warming due to increases in
greenhouse gases and natural forcing, some cooling due to other
anthropogenic forcings, and a substantial, but not implausible,
contribution from internal variability. In the second half of the
century we find that the warming is largely caused by changes in
greenhouse gases, with changes in sulphates and, perhaps, volcanic
aerosol offsetting approximately one third of the warming."
A 2005 review of detection and attribution studies by the International Ad Hoc Detection and Attribution Group
found that "natural drivers such as solar variability and volcanic
activity are at most partially responsible for the large-scale
temperature changes observed over the past century, and that a large
fraction of the warming over the last 50 yr can be attributed to
greenhouse gas increases. Thus, the recent research supports and
strengthens the IPCC Third Assessment Report conclusion that 'most of
the global warming over the past 50 years is likely due to the increase
in greenhouse gases.'"
Barnett and colleagues (2005) say that the observed warming of the
oceans "cannot be explained by natural internal climate variability or
solar and volcanic forcing, but is well simulated by two anthropogenically
forced climate models," concluding that "it is of human origin, a
conclusion robust to observational sampling and model differences".
Two papers in the journal Science in August 2005 resolve the problem, evident at the time of the TAR, of tropospheric temperature trends (see also the section on "fingerprint" studies)
. The UAH version of the record contained errors, and there is evidence
of spurious cooling trends in the radiosonde record, particularly in
the tropics. See satellite temperature measurements for details; and the 2006 US CCSP report.
A 2010 paper in the Proceedings of the National Academy of Sciences
found that among a pool of roughly 1,000 researchers who work directly
on climate issues and publish the most frequently on the subject, 97%
agree that anthropogenic climate change is happening.
A 2011 paper from George Mason University published in the International Journal of Public Opinion Research,
"The Structure of Scientific Opinion on Climate Change," collected the
opinions of scientists in the earth, space, atmospheric, oceanic or
hydrological sciences.
The 489 survey respondents—representing nearly half of all those
eligible according to the survey's specific standards – work in
academia, government, and industry, and are members of prominent
professional organizations. The study found that 97% of the 489 scientists surveyed agreed that global temperatures have risen over the past century. Moreover, 84% agreed that "human-induced greenhouse warming" is now occurring." Only 5% disagreed with the idea that human activity is a significant cause of global warming.
As described above, a small minority of scientists do disagree with the consensus: see list of scientists opposing global warming consensus. For example, Willie Soon and Richard Lindzen
say that there is insufficient proof for anthropogenic attribution.
Generally this position requires new physical mechanisms to explain the
observed warming.
Solar activity
Solar irradiance (yellow) plotted together with temperature (red) over 1880 to 2018.
Modelled
simulation of the effect of various factors (including GHGs, Solar
irradiance) singly and in combination, showing in particular that solar
activity produces a small and nearly uniform warming, unlike what is
observed.
Solar sunspot maximum occurs when the magnetic field of the sun collapses and reverse as part of its average 11 year solar cycle (22 years for complete North to North restoration).
The role of the sun in recent climate change has been looked at by climate scientists. Since 1978, output from the Sun has been measured by satellites significantly more accurately than was previously possible from the surface. These measurements indicate that the Sun's total solar irradiance
has not increased since 1978, so the warming during the past 30 years
cannot be directly attributed to an increase in total solar energy
reaching the Earth (see graph above, left). In the three decades since
1978, the combination of solar and volcanic activity probably had a slight cooling influence on the climate.
Climate models have been used to examine the role of the sun in recent climate change.
Models are unable to reproduce the rapid warming observed in recent
decades when they only take into account variations in total solar
irradiance and volcanic activity. Models are, however, able to simulate
the observed 20th century changes in temperature when they include all
of the most important external forcings, including human influences and
natural forcings. As has already been stated, Hegerl et al.
(2007) concluded that greenhouse gas forcing had "very likely" caused
most of the observed global warming since the mid-20th century. In
making this conclusion, Hegerl et al. (2007) allowed for the possibility that climate models had been underestimated the effect of solar forcing.
The role of solar activity in climate change has also been calculated over longer time periods using "proxy" datasets, such as tree rings.
Models indicate that solar and volcanic forcings can explain periods of relative warmth and cold between A.D. 1000 and 1900, but human-induced forcings are needed to reproduce the late-20th century warming.
Another line of evidence against the sun having caused recent
climate change comes from looking at how temperatures at different
levels in the Earth's atmosphere have changed.
Models and observations (see figure above, middle) show that greenhouse
gas results in warming of the lower atmosphere at the surface (called
the troposphere) but cooling of the upper atmosphere (called the stratosphere). Depletion of the ozone layer by chemical refrigerants
has also resulted in a cooling effect in the stratosphere. If the sun
was responsible for observed warming, warming of the troposphere at the
surface and warming at the top of the stratosphere would be expected as
increase solar activity would replenish ozone and oxides of nitrogen.
The stratosphere has a reverse temperature gradient than the
troposphere so as the temperature of the troposphere cools with
altitude, the stratosphere rises with altitude. Hadley cells
are the mechanism by which equatorial generated ozone in the tropics
(highest area of UV irradiance in the stratosphere) is moved poleward.
Global climate models suggest that climate change may widen the Hadley
cells and push the jetstream northward thereby expanding the tropics
region and resulting in warmer, dryer conditions in those areas overall.
Non-consensus views
Contribution of natural factors and human activities to radiative forcing of climate change. Radiative forcing values are for the year 2005, relative to the pre-industrial era (1750).
The contribution of solar irradiance to radiative forcing is 5% the
value of the combined radiative forcing due to increases in the
atmospheric concentrations of carbon dioxide, methane and nitrous oxide.
Habibullo Abdussamatov (2004), head of space research at St. Petersburg's Pulkovo Astronomical Observatory in Russia, has argued that the sun is responsible for recently observed climate change. Journalists for news sources canada.com (Solomon, 2007b), National Geographic News (Ravillious, 2007), and LiveScience (Than, 2007) reported on the story of warming on Mars.
In these articles, Abdussamatov was quoted. He stated that warming on
Mars was evidence that global warming on Earth was being caused by
changes in the sun.
Ravillious (2007) quoted two scientists who disagreed with Abdussamatov: Amato Evan, a climate scientist at the University of Wisconsin–Madison, in the US, and Colin Wilson, a planetary physicist at Oxford University in the UK. According to Wilson, "Wobbles in the orbit of Mars are the main cause of its climate change in the current era" (see also orbital forcing). Than (2007) quoted Charles Long, a climate physicist at Pacific Northwest National Laboratories in the US, who disagreed with Abdussamatov.
"I
think it is an intriguing coincidence that warming trends have been
observed on a number of very diverse planetary bodies in our solar
system, (...) Perhaps this is just a fluke."
Than (2007) provided alternative explanations of why warming had occurred on Triton, Pluto, Jupiter and Mars.
The US Environmental Protection Agency (US EPA, 2009) responded to public comments on climate change attribution.
A number of commenters had argued that recent climate change could be
attributed to changes in solar irradiance. According to the US EPA
(2009), this attribution was not supported by the bulk of the scientific literature.
Citing the work of the IPCC (2007), the US EPA pointed to the low
contribution of solar irradiance to radiative forcing since the start of
the Industrial Revolution in 1750. Over this time period (1750 to
2005),
the estimated contribution of solar irradiance to radiative forcing was
5% the value of the combined radiative forcing due to increases in the
atmospheric concentrations of carbon dioxide, methane and nitrous oxide
(see graph opposite).
Effect of cosmic rays
Henrik Svensmark has suggested that the magnetic activity of the sun deflects cosmic rays, and that this may influence the generation of cloud condensation nuclei, and thereby have an effect on the climate. The website ScienceDaily reported on a 2009 study that looked at how past changes in climate have been affected by the Earth's magnetic field.
Geophysicist Mads Faurschou Knudsen, who co-authored the study, stated
that the study's results supported Svensmark's theory. The authors of
the study also acknowledged that CO 2 plays an important role in climate change.
Consensus view on cosmic rays
The view that cosmic rays could provide the mechanism by which changes
in solar activity affect climate is not supported by the literature. Solomon et al. (2007) state:
[..]
the cosmic ray time series does not appear to correspond to global
total cloud cover after 1991 or to global low-level cloud cover after
1994. Together with the lack of a proven physical mechanism and the
plausibility of other causal factors affecting changes in cloud cover,
this makes the association between galactic cosmic ray-induced changes
in aerosol and cloud formation controversial
Studies by Lockwood and Fröhlich (2007) and Sloan and Wolfendale (2008) found no relation between warming in recent decades and cosmic rays. Pierce and Adams (2009)
used a model to simulate the effect of cosmic rays on cloud properties.
They concluded that the hypothesized effect of cosmic rays was too
small to explain recent climate change. Pierce and Adams (2009)
noted that their findings did not rule out a possible connection
between cosmic rays and climate change, and recommended further
research.
Erlykin et al. (2009)
found that the evidence showed that connections between solar variation
and climate were more likely to be mediated by direct variation of
insolation rather than cosmic rays, and concluded: "Hence within our
assumptions, the effect of varying solar activity, either by direct
solar irradiance or by varying cosmic ray rates, must be less than 0.07
°C since 1956, i.e. less than 14% of the observed global warming."
Carslaw (2009) and Pittock (2009)
review the recent and historical literature in this field and continue
to find that the link between cosmic rays and climate is tenuous, though
they encourage continued research. US EPA (2009) commented on research by Duplissy et al. (2009):
The CLOUD experiments at CERN
are interesting research but do not provide conclusive evidence that
cosmic rays can serve as a major source of cloud seeding. Preliminary
results from the experiment (Duplissy et al., 2009) suggest that though
there was some evidence of ion mediated nucleation, for most of the
nucleation events observed the contribution of ion processes appeared to
be minor. These experiments also showed the difficulty in maintaining
sufficiently clean conditions and stable temperatures to prevent
spurious aerosol bursts. There is no indication that the earlier
Svensmark experiments could even have matched the controlled conditions
of the CERN experiment. We find that the Svensmark results on cloud
seeding have not yet been shown to be robust or sufficient to materially
alter the conclusions of the assessment literature, especially given
the abundance of recent literature that is skeptical of the cosmic
ray-climate linkage
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