Global warming
Climate model projections are summarized in the 2007 Fourth Assessment Report (AR4) by the Intergovernmental Panel on Climate Change (IPCC). They indicate that during the 21st century the global surface temperature is likely to rise a further 1.1 to 2.9 °C (2 to 5.2 °F) for their lowest emissions scenario and 2.4 to 6.4 °C (4.3 to 11.5 °F) for their highest.[8] The ranges of these estimates arise from the use of models with differing sensitivity to greenhouse gas concentrations.
An increase in global temperature will cause sea levels to rise and will change the amount and pattern of precipitation, and a probable expansion of subtropical deserts.[11] 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 of the warming include more frequent occurrence of extreme weather events including heatwaves, droughts and heavy rainfall events, species extinctions due to shifting temperature regimes, and changes in crop yields. Warming and related changes will vary from region to region around the globe, with projections being more robust in some areas than others.[12] In a 4 °C world, the limits for human adaptation are likely to be exceeded in many parts of the world, while the limits for adaptation for natural systems would largely be exceeded throughout the world. Hence, the ecosystem services upon which human livelihoods depend would not be preserved.[13]
Most countries are parties to the United Nations Framework Convention on Climate Change (UNFCCC),[14] whose ultimate objective is to prevent "dangerous" anthropogenic (i.e., human-induced) climate change.[15] Parties to the UNFCCC have adopted a range of policies designed to reduce greenhouse gas emissions[16]:10[17][18][19]:9 and to assist in adaptation to global warming.[16]:13[19]:10[20][21] Parties to the UNFCCC have agreed that deep cuts in emissions are required,[22] and that future global warming should be limited to below 2.0 °C (3.6 °F) relative to the pre-industrial level.[22][B] Analyses by the United Nations Environment Programme (published in 2011)[23] and International Energy Agency (2011)[24] suggest that current efforts to reduce emissions may be inadequately stringent to meet the UNFCCC's 2 °C target.
Global mean land-ocean temperature change from 1880–2010, relative to the 1951–1980 mean. The black line is the annual mean and the red line is the 5-year running mean. The green bars show uncertainty estimates. Source: NASA GISS
The map shows the 10-year average (2000–2009) global mean temperature anomaly relative to the 1951–1980 mean. The largest temperature increases are in the Arctic and the Antarctic Peninsula. Source: NASA Earth Observatory[1]
Fossil fuel related CO2 emissions compared to five of IPCC's emissions scenarios. The dips are related to global recessions. Data from IPCC SRES scenarios; Data spreadsheet included with International Energy Agency's "CO2 Emissions from Fuel Combustion 2010 – Highlights"; and Supplemental IEA data. Image source: Skeptical Science
Observed temperature changes
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.[25][26][27] The Earth's average surface temperature, expressed as a linear trend, 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±0.02 °C per decade). The urban heat island effect is very small, estimated to account for less than 0.002 °C of warming per decade since 1900.[28] 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. Climate proxies show the temperature 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.[29]Recent estimates by NASA's Goddard Institute for Space Studies (GISS) and the National Climatic Data Center show that 2005 and 2010 tied for the planet's warmest year since reliable, widespread instrumental measurements became available in the late 19th century, exceeding 1998 by a few hundredths of a degree.[30][31][32] Current estimates by the Climatic Research Unit (CRU) show 2005 as the second warmest year, behind 1998 with 2003 and 2010 tied for third warmest year, however, “the error estimate for individual years ... is at least ten times larger than the differences between these three years.”[33] The World Meteorological Organization (WMO) statement on the status of the global climate in 2010 explains that, “The 2010 nominal value of +0.53 °C ranks just ahead of those of 2005 (+0.52 °C) and 1998 (+0.51 °C), although the differences between the three years are not statistically significant...”[34]
Temperatures in 1998 were unusually warm because the strongest El Niño in the past century occurred during that year.[35] 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.[36][37]
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).[38] 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.[39] 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.[40]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.
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.[156] 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."[157][158] A 2010 poll by the Office of National Statistics found that 75% of UK respondents were at least "fairly convinced" that the world's climate is changing, compared to 87% in a similar survey in 2006.[159] A January 2011 ICM poll in the UK found 83% of respondents viewed climate change as a current or imminent threat, while 14% said it was no threat. Opinion was unchanged from an August 2009 poll asking the same question, though there had been a slight polarisation of opposing views.[160]A survey in October, 2009 by the Pew Research Center for the People & the Press showed decreasing public perception in the United States that global warming was a serious problem. All political persuasions showed reduced concern with lowest concern among Republicans, only 35% of whom considered there to be solid evidence of global warming.[161] The cause of this marked difference in public opinion between the United States and the global public is uncertain but the hypothesis has been advanced that clearer communication by scientists both directly and through the media would be helpful in adequately informing the American public of the scientific consensus and the basis for it.[162] The U.S. public appears to be unaware of the extent of scientific consensus regarding the issue, with 59% believing that scientists disagree "significantly" on global warming.[163]
By 2010, with 111 countries surveyed, Gallup determined that there was a substantial decrease in the number of Americans and Europeans who viewed Global Warming as a serious threat. In the United States, a little over half the population (53%) now viewed it as a serious concern for either themselves or their families; a number 10 percentage points below the 2008 poll (63%). Latin America had the biggest rise in concern, with 73% saying global warming was a serious threat to their families.[164] That global poll also found that people are more likely to attribute global warming to human activities than to natural causes, except in the USA where nearly half (47%) of the population attributed global warming to natural causes.[165]
On the other hand, in May 2011 a joint poll by Yale and George Mason Universities found that nearly half the people in the USA (47%) attribute global warming to human activities, compared to 36% blaming it on natural causes. Only 5% of the 35% who were "disengaged", "doubtful", or "dismissive" of global warming were aware that 97% of publishing US climate scientists agree global warming is happening and is primarily caused by humans.[166]
Researchers at the University of Michigan have found that the public's belief as to the causes of global warming depends on the wording choice used in the polls.[167]
In the United States, according to the Public Policy Institute of California's (PPIC) eleventh annual survey on environmental policy issues, 75% said they believe global warming is a very serious or somewhat serious threat to the economy and quality of life in California.[168]
A July 2011 Rasmussen Reports poll found that 69% of adults in the USA believe it is at least somewhat likely that some scientists have falsified global warming research.[155]
A September 2011 Angus Reid Public Opinion poll found that Britons (43%) are less likely than Americans (49%) or Canadians (52%) to say that "global warming is a fact and is mostly caused by emissions from vehicles and industrial facilities." The same poll found that 20% of Americans, 20% of Britons and 14% of Canadians think "global warming is a theory that has not yet been proven."
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