Global warming
From Wikipedia, the free encyclopedia
For scientific and political disputes, see Global warming controversy, Scientific
opinion on climate change and Public opinion on climate change.
For past climate change see Paleoclimatology and Geologic temperature record.
For the Sonny Rollins album see Global Warming (album).
1880-2009 global mean surface temperature difference relative to the 1961–1990 average. Data
source: NASA GISS
Comparison of ground based (blue) and satellite based (red: UAH; green: RSS) records of
temperature variations since 1979. Trends plotted since January 1982.
Mean surface temperature change for the period 2000 to 2009 relative to the average temperatures
from 1951 to 1980.[1]
Global warming is the increase in the average temperature of Earth's near-surface
air and oceans since the mid-20th century and its projected continuation. According
to the 2007 Fourth Assessment Report by the Intergovernmental Panel on Climate
Change (IPCC), global surface temperature increased 0.74 ± 0.18 ° C
(1.33 ± 0.32 ° F) during the 20th century.[2][A] Most of the observed temperature
increase since the middle of the 20th century has been caused by increasing
concentrations of greenhouse gases, which result from human activity such as the
burning of fossil fuel and deforestation.[3] Global dimming, a result of increasing
concentrations of atmospheric aerosols that block sunlight from reaching the
surface, has partially countered the effects of warming induced by greenhouse
gases.
Climate model projections summarized in the latest IPCC report indicate that the
global surface temperature is likely to rise a further 1.1 to 6.4 ° C (2.0 to 11.5 ° F)
during the 21st century.[2] The uncertainty in this estimate arises from the use of
models with differing sensitivity to greenhouse gas concentrations and the use of
differing estimates of future greenhouse gas emissions. An increase in global
temperature will cause sea levels to rise and will change the amount and pattern of
precipitation, probably including expansion of subtropical deserts.[4] Warming is
expected to be strongest in the Arctic and would be associated with continuing
retreat of glaciers, permafrost and sea ice. Other likely effects include changes in
the frequency and intensity of extreme weather events, species extinctions, and
changes in agricultural yields. Warming and related changes will vary from region to
region around the globe, though the nature of these regional variations is uncertain.
[5] As a result of contemporary increases in atmospheric carbon dioxide, the oceans
have become more acidic, a result that is predicted to continue.[6][7]
The scientific consensus is that anthropogenic global warming is occurring.[8][9][10]
[B] Nevertheless, political and public debate continues. The Kyoto Protocol is aimed
at stabilizing greenhouse gas concentration to prevent a "dangerous anthropogenic
interference".[11] As of November 2009, 187 states had signed and ratified the
protocol.[12]
Proposed responses to climate change include mitigation to reduce emissions,
adaptation to the effects of global warming, and geoengineering to remove
greenhouse gases from the atmosphere or block incoming sunlight.
Contents [hide]
1 1 Temperature changes
2 2 External forcings
1 2.1 Greenhouse
gases
2 2.2 Aerosols and
soot
3 2.3 Solar variation
3 3 Feedback
4 4 Climate models
5 5 Attributed and expected
effects
1 5.1 Natural systems
2 5.2 Ecological
systems
3 5.3 Social systems
6 6 Responses to global
warming
1 6.1 Mitigation
2 6.2 Adaptation
3 6.3
Geoengineering
4 6.4 UNFCCC
7 7 Views on global warming
1 7.1 Politics
2 7.2 Public opinion
3 7.3 Other views
8 8 Etymology
9 9 See also
1010 Notes
11 11 References
1212 Further reading
1313 External links
Temperature changes
Main article: Temperature record
Two millennia of mean surface temperatures according to different reconstructions, each smoothed
on a decadal scale, with the actual recorded temperatures overlaid in black.
Evidence for warming of the climate system includes observed increases in global
average air and ocean temperatures, widespread melting of snow and ice, and
rising global average sea level.[13][14][15][16][17] The most common measure of
global warming is the trend in globally averaged temperature near the Earth's
surface. Expressed as a linear trend, this temperature rose by 0.74 ± 0.18 ° C over
the period 1906–2005. The rate of warming over the last half of that period was
almost double that for the period as a whole (0.13 ± 0.03 ° C per decade, versus
0.07 ° C ± 0.02 ° C per decade). The urban heat island effect is estimated to
account for about 0.002 ° C of warming per decade since 1900.[18] Temperatures in
the lower troposphere have increased between 0.13 and 0.22 ° C (0.22 and 0.4 °F)
per decade since 1979, according to satellite temperature measurements.
Temperature is believed to have been relatively stable over the one or two thousand
years before 1850, with regionally varying fluctuations such as the Medieval Warm
Period and the Little Ice Age.[19]
Estimates by NASA's Goddard Institute for Space Studies (GISS) and the National
Climatic Data Center show that 2005 was the warmest year since reliable,
widespread instrumental measurements became available in the late 19th century,
exceeding the previous record set in 1998 by a few hundredths of a degree.[20][21]
Estimates prepared by the World Meteorological Organization and the Climatic
Research Unit show 2005 as the second warmest year, behind 1998.[22][23]
Temperatures in 1998 were unusually warm because the strongest El Niño in the
past century occurred during that year.[24] Global temperature is subject to short-
term fluctuations that overlay long term trends and can temporarily mask them. The
relative stability in temperature from 2002 to 2009 is consistent with such an
episode.[25][26]
Temperature changes vary over the globe. Since 1979, land temperatures have
increased about twice as fast as ocean temperatures (0.25 ° C per decade against
0.13 ° C per decade).[27] Ocean temperatures increase more slowly than land
temperatures because of the larger effective heat capacity of the oceans and
because the ocean loses more heat by evaporation.[28] The Northern Hemisphere
warms faster than the Southern Hemisphere because it has more land and because
it has extensive areas of seasonal snow and sea-ice cover subject to ice-albedo
feedback. Although more greenhouse gases are emitted in the Northern than
Southern Hemisphere this does not contribute to the difference in warming because
the major greenhouse gases persist long enough to mix between hemispheres.[29]
The thermal inertia of the oceans and slow responses of other indirect effects mean
that climate can take centuries or longer to adjust to changes in forcing. Climate
commitment studies indicate that even if greenhouse gases were stabilized at 2000
levels, a further warming of about 0.5 ° C (0.9 ° F) would still occur.[30]
External forcings
External forcing refers to processes external to the climate system (though not
necessarily external to Earth) that influence climate. Climate responds to several
types of external forcing, such as radiative forcing due to changes in atmospheric
composition (mainly greenhouse gas concentrations), changes in solar luminosity,
volcanic eruptions, and variations in Earth's orbit around the Sun.[31] Attribution of
recent climate change focuses on the first three types of forcing. Orbital cycles vary
slowly over tens of thousands of years and thus are too gradual to have caused the
temperature changes observed in the past century.
Greenhouse gases
Main articles: Greenhouse effect, Radiative forcing, and Carbon dioxide in Earth's
atmosphere
Greenhouse effect schematic showing energy flows between space, the atmosphere, and earth's
surface. Energy exchanges are expressed in watts per square meter (W/m2).
Recent atmospheric carbon dioxide (CO2) increases. Monthly CO2 measurements display
seasonal oscillations in overall yearly uptrend; each year's maximum occurs during the Northern
Hemisphere's late spring, and declines during its growing season as plants remove some
atmospheric CO2.
The greenhouse effect is the process by which absorption and emission of infrared
radiation by gases in the atmosphere warm a planet's lower atmosphere and
surface. It was proposed by Joseph Fourier in 1824 and was first investigated
quantitatively by Svante Arrhenius in 1896.[32]
Naturally occurring greenhouse gases have a mean warming effect of about 33 °C
(59 ° F).[33][C] The major greenhouse gases are water vapor, which causes about
36–70 percent of the greenhouse effect; carbon dioxide (CO2), which causes 9–26
percent; methane (CH4), which causes 4–9 percent; and ozone (O3), which causes
3–7 percent.[34][35][36] Clouds also affect the radiation balance, but they are
composed of liquid water or ice and so have different effects on radiation from water
vapor.
Human activity since the Industrial Revolution has increased the amount of
greenhouse gases in the atmosphere, leading to increased radiative forcing from
CO2, methane, tropospheric ozone, CFCs and nitrous oxide. The concentrations of
CO2 and methane have increased by 36% and 148% respectively since 1750.[37]
These levels are much higher than at any time during the last 650,000 years, the
period for which reliable data has been extracted from ice cores.[38][39][40] Less
direct geological evidence indicates that CO2 values higher than this were last seen
about 20 million years ago.[41] Fossil fuel burning has produced about three-
quarters of the increase in CO2 from human activity over the past 20 years. Most of
the rest is due to land-use change, particularly deforestation.[42]
Over the last three decades of the 20th century, GDP per capita and population
growth were the main drivers of increases in greenhouse gas emissions.[43] CO2
emissions are continuing to rise due to the burning of fossil fuels and land-use
change.[44][45]:71 Emissions scenarios, estimates of changes in future emission
levels of greenhouse gases, have been projected that depend upon uncertain
economic, sociological, technological, and natural developments.[46] In most
scenarios, emissions continue to rise over the century, while in a few, emissions are
reduced.[47][48] These emission scenarios, combined with carbon cycle modelling,
have been used to produce estimates of how atmospheric concentrations of
greenhouse gases will change in the future. Using the six IPCC SRES "marker"
scenarios, models suggest that by the year 2100, the atmospheric concentration of
CO2 could range between 541 and 970 ppm.[49] This is an increase of 90-250%
above the concentration in the year 1750. Fossil fuel reserves are sufficient to reach
these levels and continue emissions past 2100 if coal, oil sands or methane
clathrates are extensively exploited.[50]
The destruction of stratospheric ozone by chlorofluorocarbons is sometimes
mentioned in relation to global warming. Although there are a few areas of linkage,
the relationship between the two is not strong. Reduction of stratospheric ozone has
a cooling influence.[51] Substantial ozone depletion did not occur until the late
1970s.[52] Ozone in the troposphere (the lowest part of the Earth's atmosphere)
does contribute to surface warming.[53]
Aerosols and soot
Ship tracks over the Atlantic Ocean on the east coast of the United States. The climatic impacts
from aerosol forcing could have a large effect on climate through the indirect effect.
Global dimming, a gradual reduction in the amount of global direct irradiance at the
Earth's surface, has partially counteracted global warming from 1960 to the present.
[54] The main cause of this dimming is aerosols produced by volcanoes and
pollutants. These aerosols exert a cooling effect by increasing the reflection of
incoming sunlight. The effects of the products of fossil fuel combustion—CO2 and
aerosols—have largely offset one another in recent decades, so that net warming
has been due to the increase in non-CO2 greenhouse gases such as methane.[55]
Radiative forcing due to aerosols is temporally limited due to wet deposition which
causes aerosols to have an atmospheric lifetime of one week. Carbon dioxide has a
lifetime of a century or more, and as such, changes in aerosol concentrations will
only delay climate changes due to carbon dioxide.[56]
In addition to their direct effect by scattering and absorbing solar radiation, aerosols
have indirect effects on the radiation budget.[57] Sulfate aerosols act as cloud
condensation nuclei and thus lead to clouds that have more and smaller cloud
droplets. These clouds reflect solar radiation more efficiently than clouds with fewer
and larger droplets.[58] This effect also causes droplets to be of more uniform size,
which reduces growth of raindrops and makes the cloud more reflective to incoming
sunlight.[59] Indirect effects are most noticeable in marine stratiform clouds, and
have very little radiative effect on convective clouds. Aerosols, particularly their
indirect effects, represent the largest uncertainty in radiative forcing.[60]
Soot may cool or warm the surface, depending on whether it is airborne or
deposited. Atmospheric soot aerosols directly absorb solar radiation, which heats
the atmosphere and cools the surface. In isolated areas with high soot production,
such as rural India, as much as 50% of surface warming due to greenhouse gases
may be masked by atmospheric brown clouds.[61] Atmospheric soot always
contributes additional warming to the climate system. When deposited, especially
on glaciers or on ice in arctic regions, the lower surface albedo can also directly
heat the surface.[62] The influences of aerosols, including black carbon, are most
pronounced in the tropics and sub-tropics, particularly in Asia, while the effects of
greenhouse gases are dominant in the extratropics and southern hemisphere.[63]
Solar variation
Main article: Solar variation
Solar variation over thirty years.
Variations in solar output have been the cause of past climate changes.[64] The
effect of changes in solar forcing in recent decades is uncertain, but small, with
some studies showing a slight cooling effect,[65] while others studies suggest a
slight warming effect.[31][66][67][68]
Greenhouse gases and solar forcing affect temperatures in different ways. While
both increased solar activity and increased greenhouse gases are expected to
warm the troposphere, an increase in solar activity should warm the stratosphere
while an increase in greenhouse gases should cool the stratosphere.[31]
Observations show that temperatures in the stratosphere have been cooling since
1979, when satellite measurements became available. Radiosonde (weather
balloon) data from the pre-satellite era show cooling since 1958, though there is
greater uncertainty in the early radiosonde record.[69]
A related hypothesis, proposed by Henrik Svensmark, is that magnetic activity of
the sun deflects cosmic rays that may influence the generation of cloud
condensation nuclei and thereby affect the climate.[70] Other research has found no
relation between warming in recent decades and cosmic rays.[71][72] The influence
of cosmic rays on cloud cover is about a factor of 100 lower than needed to explain
the observed changes in clouds or to be a significant contributor to present-day
climate change.[73]
Feedback
Main article: Climate change feedback
Feedback is a process in which changing one quantity changes a second quantity,
and the change in the second quantity in turn changes the first. Positive feedback
amplifies the change in the first quantity while negative feedback reduces it.
Feedback is important in the study of global warming because it may amplify or
diminish the effect of a particular process. The main positive feedback in global
warming is the tendency of warming to increase the amount of water vapor in the
atmosphere, a significant greenhouse gas. The main negative feedback is radiative
cooling, which increases as the fourth power of temperature; the amount of heat
radiated from the Earth into space increases with the temperature of Earth's surface
and atmosphere. Imperfect understanding of feedbacks is a major cause of
uncertainty and concern about global warming. A wide range of potential feedback
process exist, such as Arctic methane release and ice-albedo feedback.
Consequentially, potential tipping points may exist, which may have the potential to
cause abrupt climate change.[74]
Climate models
Main article: Global climate model
Calculations of global warming prepared in or before 2001 from a range of climate models under
the SRES A2 emissions scenario, which assumes no action is taken to reduce emissions and
regionally divided economic development.
The geographic distribution of surface warming during the 21st century calculated by the HadCM3
climate model if a business as usual scenario is assumed for economic growth and greenhouse
gas emissions. In this figure, the globally averaged warming corresponds to 3.0 ° C (5.4 ° F).
The main tools for projecting future climate changes are mathematical models
based on physical principles including fluid dynamics, thermodynamics and
radiative transfer. Although they attempt to include as many processes as possible,
simplifications of the actual climate system are inevitable because of the constraints
of available computer power and limitations in knowledge of the climate system. All
modern climate models are in fact combinations of models for different parts of the
Earth. These include an atmospheric model for air movement, temperature, clouds,
and other atmospheric properties; an ocean model that predicts temperature, salt
content, and circulation of ocean waters; models for ice cover on land and sea; and
a model of heat and moisture transfer from soil and vegetation to the atmosphere.
Some models also include treatments of chemical and biological processes.[75]
Warming due to increasing levels of greenhouse gases is not an assumption of the
models; rather, it is an end result from the interaction of greenhouse gases with
radiative transfer and other physical processes.[76] Although much of the variation
in model outcomes depends on the greenhouse gas emissions used as inputs, the
temperature effect of a specific greenhouse gas concentration (climate sensitivity)
varies depending on the model used. The representation of clouds is one of the
main sources of uncertainty in present-generation models.[77]
Global climate model projections of future climate most often have used estimates
of greenhouse gas emissions from the IPCC Special Report on Emissions
Scenarios (SRES). In addition to human-caused emissions, some models also
include a simulation of the carbon cycle; this generally shows a positive feedback,
though this response is uncertain. Some observational studies also show a positive
feedback.[78][79][80] Including uncertainties in future greenhouse gas concentrations
and climate sensitivity, the IPCC anticipates a warming of 1.1 ° C to 6.4 ° C (2.0 ° F
to 11.5 °F) by the end of the 21st century, relative to 1980–1999.[2]
Models are also used to help investigate the causes of recent climate change by
comparing the observed changes to those that the models project from various
natural and human-derived causes. Although these models do not unambiguously
attribute the warming that occurred from approximately 1910 to 1945 to either
natural variation or human effects, they do indicate that the warming since 1970 is
dominated by man-made greenhouse gas emissions.[31]
The physical realism of models is tested by examining their ability to simulate
current or past climates.[81] Current climate models produce a good match to
observations of global temperature changes over the last century, but do not
simulate all aspects of climate.[42] Not all effects of global warming are accurately
predicted by the climate models used by the IPCC. Observed Arctic shrinkage has
been faster than that predicted.[82] Precipitation increased proportional to
atmospheric humidity, and hence significantly faster than current global climate
models predict.[83][84]
Attributed and expected effects
Main articles: Effects of global warming and Regional effects of global warming
Global warming may be detected in natural, ecological or social systems as a
change having statistical significance.[85] Attribution of these changes e.g., to
natural or human activities, is the next step following detection.[86]
Natural systems
Sparse records indicate that glaciers have been retreating since the early 1800s. In the 1950s
measurements began that allow the monitoring of glacial mass balance, reported to the WGMS
and the NSIDC.
Global warming has been detected in a number of systems. Some of these
changes, e.g., based on the instrumental temperature record, have been described
in the section on temperature changes. Rising sea levels and observed decreases
in snow and ice extent are consistent with warming.[17] Most of the increase in
global average temperature since the mid-20th century is, with high probability,[D]
attributable to human-induced changes in greenhouse gas concentrations.[87]
Even with current policies to reduce emissions, global emissions are still expected
to continue to grow over the coming decades.[88] Over the course of the 21st
century, increases in emissions at or above their current rate would very likely
induce changes in the climate system larger than those observed in the 20th
century.
In the IPCC Fourth Assessment Report, across a range of future emission
scenarios, model-based estimates of sea level rise for the end of the 21st century
(the year 2090-2099, relative to 1980-1999) range from 0.18 to 0.59 m. These
estimates, however, were not given a likelihood due to a lack of scientific
understanding, nor was an upper bound given for sea level rise. Over the course of
centuries to millennia, the melting of ice sheets could result in sea level rise of 4–
6 m or more.[89]
Changes in regional climate are expected to include greater warming over land, with
most warming at high northern latitudes, and least warming over the Southern
Ocean and parts of the North Atlantic Ocean.[88] Snow cover area and sea ice
extent are expected to decrease. The frequency of hot extremes, heat waves, and
heavy precipitation will very likely increase.
Ecological systems
In terrestrial ecosystems, the earlier timing of spring events, and poleward and
upward shifts in plant and animal ranges, have been linked with high confidence to
recent warming.[17] Future climate change is expected to particularly affect certain
ecosystems, including tundra, mangroves, and coral reefs.[88] It is expected that
most ecosystems will be affected by higher atmospheric CO2 levels, combined with
higher global temperatures.[90] Overall, it is expected that climate change will result
in the extinction of many species and reduced diversity of ecosystems.[91]
Social systems
There is some evidence of regional climate change affecting systems related to
human activities, including agricultural and forestry management activities at higher
latitudes in the Northern Hemisphere.[17] Future climate change is expected to
particularly affect some sectors and systems related to human activities.[88] Low-
lying coastal systems are vulnerable to sea level rise and storm surge. Human
health will be at increased risk in populations with limited capacity to adapt to
climate change. It is expected that some regions will be particularly affected by
climate change, including the Arctic, Africa, small islands, and Asian and African
megadeltas. In some areas the effects on agriculture, industry and health could be
mixed, or even beneficial in certain respects, but overall it is expected that these
benefits will be outweighed by negative effects.[92]
Responses to global warming
Mitigation
Main article: Climate change mitigation
See also: Fee and dividend
Reducing the amount of future climate change is called mitigation of climate
change. The IPCC defines mitigation as activities that reduce greenhouse gas
(GHG) emissions, or enhance the capacity of carbon sinks to absorb GHGs from
the atmosphere.[93] Many countries, both developing and developed, are aiming to
use cleaner, less polluting, technologies.[45]:192 Use of these technologies aids
mitigation and could result in substantial reductions in CO2 emissions. Policies
include targets for emissions reductions, increased use of renewable energy, and
increased energy efficiency. Studies indicate substantial potential for future
reductions in emissions.[94] Since even in the most optimistic scenario, fossil fuels
are going to be used for years to come, mitigation may also involve carbon capture
and storage, a process that traps CO2 produced by factories and gas or coal power
stations and then stores it, usually underground.[95]
Adaptation
Main article: Adaptation to global warming
Other policy responses include adaptation to climate change. Adaptation to climate
change may be planned, e.g., by local or national government, or spontaneous, i.e.,
done privately without government intervention.[96] The ability to adapt is closely
linked to social and economic development.[94] Even societies with high capacities
to adapt are still vulnerable to climate change. Planned adaptation is already
occurring on a limited basis. The barriers, limits, and costs of future adaptation are
not fully understood.
Geoengineering
Another policy response is engineering of the climate (geoengineering). This policy
response is sometimes grouped together with mitigation.[97] Geoengineering is
largely unproven, and reliable cost estimates for it have not yet been published.[98]
Geoengineering encompasses a range of techniques to remove CO2 from the
atmosphere or to block incoming sunlight.
UNFCCC
Most countries are Parties to the United Nations Framework Convention on Climate
Change (UNFCCC).[99] The ultimate objective of the Convention is to prevent
"dangerous" human interference of the climate system.[100] As is stated in the
Convention, this requires that GHGs are stabilized in the atmosphere at a level
where ecosystems can adapt naturally to climate change, food production is not
threatened, and economic development can proceed in a sustainable fashion.
The UNFCCC recognizes differences among countries in their responsibility to act
on climate change.[101] In the Kyoto Protocol to the UNFCCC, most developed
countries (listed in Annex I of the treaty) took on legally binding commitments to
reduce their emissions.[102] Policy measures taken in response to these
commitments have reduced emissions.[103] For many developing (non-Annex I)
countries, reducing poverty is their overriding aim.[104]
At the 15th UNFCCC Conference of the Parties, held in 2009 at Copenhagen,
several UNFCCC Parties produced the Copenhagen Accord.[105] Parties agreeing
with the Accord aim to limit the future increase in global mean temperature to below
2 °C. [106] The 16th Conference of the Parties (COP16) was held at Cancún in 2010.
It produced an agreement, not a binding treaty, that the Parties should take urgent
action to reduce greenhouse gas emissions to meet the 2 ° C goal. It also
recognized the need to consider strengthening the goal to a global average rise of
1.5 ° C. [107]
Views on global warming
Main articles: Global warming controversy and Politics of global warming
See also: Scientific opinion on climate change and Public opinion on climate
change
Per capita greenhouse gas emissions in 2000, including land-use change.
Total greenhouse gas emissions in 2000, including land-use change.
There are different views over what the appropriate policy response to climate
change should be.[108][109] These competing views weigh the benefits of limiting
emissions of greenhouse gases against the costs. In general, it seems likely that
climate change will impose greater damages and risks in poorer regions.[110]
Politics
Developed and developing countries have made different arguments over who
should bear the burden of economic costs for cutting emissions. Developing
countries often concentrate on per capita emissions, that is, the total emissions of
a country divided by its population.[111] Per capita emissions in the industrialized
countries are typically as much as ten times the average in developing countries.
[112] This is used to make the argument that the real problem of climate change is
due to the profligate and unsustainable lifestyles of those living in rich countries.[111]
On the other hand, commentators from developed countries point out that total
carbon emissions,[111] carrying capacity, efficient energy use and civil and political
rights are very important issues. World population is the number of humans per unit
area. However the land is not the same everywhere. Not only the quantity of fossil
fuel use but also the quality of energy use is a key debate point. For example,
efficient energy use supporting technological change might help reduce excess
carbon dioxide in Earth's atmosphere. The use of fossil fuels for conspicuous
consumption and excessive entertainment are issues that can conflict with civil and
political rights. People in developed countries argue that history has proven the
difficulty of implementing fair rationing programs in different countries because
there is no global system of checks and balances or civil liberties.
The Kyoto Protocol, which came into force in 2005, sets legally binding emission
limitations for most developed countries.[102] Developing countries are not subject
to limitations. This exemption led the U.S. and Australia to decide not to ratify the
treaty,[113] [114][115] although Australia did finally ratify the treaty in December 2007.
[116] Debate continued at the Copenhagen climate summit and the Cancún climate
summit.
Public opinion
In 2007–2008 Gallup Polls surveyed 127 countries. Over a third of the world's
population was unaware of global warming, with people in developing countries less
aware than those in developed, and those in Africa the least aware. Of those aware,
Latin America leads in belief that temperature changes are a result of human
activities while Africa, parts of Asia and the Middle East, and a few countries from
the Former Soviet Union lead in the opposite belief.[117] In the Western world,
opinions over the concept and the appropriate responses are divided. Nick Pidgeon
of Cardiff University said that "results show the different stages of engagement
about global warming on each side of the Atlantic", adding, "The debate in Europe
is about what action needs to be taken, while many in the U.S. still debate whether
climate change is happening."[118][119]
Other views
Most scientists accept that humans are contributing to observed climate change.[44]
[120] National science academies have called on world leaders for policies to cut
global emissions.[121] However, some scientists and non-scientists question
aspects of climate-change science.[122][123]
Organizations such as the libertarian Competitive Enterprise Institute, conservative
commentators, and some companies such as ExxonMobil have challenged IPCC
climate change scenarios, funded scientists who disagree with the scientific
consensus, and provided their own projections of the economic cost of stricter
controls.[124][125][126][127] In the finance industry, Deutsche Bank has set up an
institutional climate change investment division (DBCCA),[128] which has
commissioned and published research[129] on the issues and debate surrounding
global warming.[130] Environmental organizations and public figures have
emphasized changes in the current climate and the risks they entail, while
promoting adaptation to changes in infrastructural needs and emissions reductions.
[131] Some fossil fuel companies have scaled back their efforts in recent years,[132]
or called for policies to reduce global warming.[133]
Etymology
The term global warming was probably first used in its modern sense on 8 August
1975 in a science paper by Wally Broecker in the journal Science called "Are we on
the brink of a pronounced global warming?".[134][135][136] Broecker's choice of
words was new and represented a significant recognition that the climate was
warming; previously the phrasing used by scientists was "inadvertent climate
modification," because while it was recognized humans could change the climate,
no one was sure which direction it was going.[137] The National Academy of
Sciences first used global warming in a 1979 paper called the Charney Report, it
said: "if carbon dioxide continues to increase, [we find] no reason to doubt that
climate changes will result and no reason to believe that these changes will be
negligible."[138] The report made a distinction between referring to surface
temperature changes as global warming, while referring to other changes caused
by increased CO2 as climate change.[137] This distinction is still often used in
science reports, with global warming meaning surface temperatures, and climate
change meaning other changes (increased storms, etc..)[137]
Global warming became more widely popular after 1988 when NASA scientist
James Hansen used the term in a testimony to Congress.[137] He said: "global
warming has reached a level such that we can ascribe with a high degree of
confidence a cause and effect relationship between the greenhouse effect and the
observed warming."[139] His testimony was widely reported and afterward global
warming was commonly used by the press and in public discourse.[137]
