Global warming From Wikipedia, the free encyclopedia This article is about the current change in Earth's climate. For general discuss ion of how the climate can change, see Climate change. For other uses, see Globa l warming (disambiguation). Page semi-protectedThis is a featured article. Click here for more information. refer to caption Global mean land-ocean temperature change from 1880?2012, relative to the 1951?1 980 mean. The black line is the annual mean and the red line is the 5-year runni ng mean. The green bars show uncertainty estimates. Source: NASA GISS. (click fo r larger image) Map of temperature changes across the world key to above map of temperature changes The map shows the 10-year average (2000?2009) global mean temperature anomaly re lative to the 1951?1980 mean. The largest temperature increases are in the Arcti c and the Antarctic Peninsula. Source: NASA Earth Observatory[1] refer to caption Fossil fuel related carbon dioxide (CO2) emissions compared to five of the IPCC' s "SRES" emissions scenarios. The dips are related to global recessions. Image s ource: Skeptical Science. Global warming refers to an unequivocal and continuing rise in the average tempe rature of Earth's climate system.[2] Since 1971, 90% of the warming has occurred in the oceans.[3] Despite the oceans' dominant role in energy storage, the term "global warming" is also used to refer to increases in average temperature of t he air and sea at Earth's surface.[4][5] Since the early 20th century, the globa l air and sea surface temperature has increased about 0.8 C (1.4 F), with about two- thirds of the increase occurring since 1980.[6] Each of the last three decades h as been successively warmer at the Earthfs surface than any preceding decade sinc e 1850.[7] Scientific understanding of the cause of global warming has been increasing. In its fourth assessment (AR4 2007) of the relevant scientific literature, the Inte rnational Panel on Climate Change (IPCC) reported that scientists were more than 90% certain that most of global warming was being caused by increasing concentr ations of greenhouse gases produced by human activities.[8][9][10] In 2010 that finding was recognized by the national science academies of all major industrial ized nations.[11][A] Affirming these findings in 2013, the IPCC stated that the largest driver of global warming is carbon dioxide (CO2) emissions from fossil f uel combustion, cement production, and land use changes such as deforestation.[1 2] Its 2013 report states Human influence has been detected in warming of the atmosphere and the ocean, in changes in the global water cycle, in reductions in snow and ice, in global mea n sea level rise, and in changes in some climate extremes. This evidence for hum an influence has grown since AR4. It is extremely likely (95-100%) that human in fluence has been the dominant cause of the observed warming since the mid-20th c entury. ?IPCC AR5 WG1 Summary for Policymakers[13] Climate model projections were summarized in the 2007 Fourth Assessment Report ( AR4) by the Intergovernmental Panel on Climate Change (IPCC). They indicated tha t during the 21st century the global surface temperature is likely to rise a fur ther 1.1 to 2.9 C (2.0 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.[14] The ranges of these estimates arise from th e use of models with differing sensitivity to greenhouse gas concentrations.[15] [16] Future climate change and associated impacts will vary from region to region aro und the globe.[17][18] The effects of an increase in global temperature include a rise in sea levels and a change in the amount and pattern of precipitation, as well as a probable expansion of subtropical deserts.[19] Warming is expected to be strongest in the Arctic, with the continuing retreat of glaciers, permafrost and sea ice. Other likely effects of the warming include more frequent extreme weather events including heat waves, droughts and heavy rainfall; ocean acidific ation; and species extinctions due to shifting temperature regimes. Effects sign ificant to humans include the threat to food security from decreasing crop yield s and the loss of habitat from inundation.[20][21] Proposed policy responses to global warming include mitigation by emissions redu ction, adaptation to its effects, and possible future geoengineering. Most count ries are parties to the United Nations Framework Convention on Climate Change (U NFCCC),[22] whose ultimate objective is to prevent dangerous anthropogenic (i.e. , human-induced) climate change.[23] Parties to the UNFCCC have adopted a range of policies designed to reduce greenhouse gas emissions[24]:10[25][26][27]:9 and to assist in adaptation to global warming.[24]:13[27]:10[28][29] Parties to the UNFCCC have agreed that deep cuts in emissions are required,[30] and that futur e global warming should be limited to below 2.0 C (3.6 F) relative to the pre-indust rial level.[30][B] Reports published in 2011 by the United Nations Environment P rogramme[31] and the International Energy Agency[32] suggest that efforts as of the early 21st century to reduce emissions may be inadequate to meet the UNFCCC' s 2 C target. Emissions of greenhouse gases grew 2.2% per year between 2000 and 2010, compared with 1.3% per year from 1970 to 2000.[33] Contents [hide] 1 Observed temperature changes 2 Initial causes of temperature changes (external forcings) 2.1 Greenhouse gases 2.2 Particulates and soot 2.3 Solar activity 3 Feedback 4 Climate models 5 Observed and expected environmental effects 5.1 Natural systems 5.2 Ecological systems 5.3 Long-term effects 5.4 Large-scale and abrupt impacts 6 Observed and expected effects on social systems 6.1 Food security 6.2 Habitat inundation 7 Proposed policy responses to global warming 7.1 Mitigation 7.2 Adaptation 8 Discourse about global warming 8.1 Political discussion 8.2 Scientific discussion 8.3 Discussion by the public and in popular media 8.3.1 Surveys of public opinion 9 Etymology 10 See also 11 Notes 12 Citations 13 References 14 Further reading 15 External links Observed temperature changes Main article: Instrumental temperature record refer to caption and adjacent text Two millennia of mean surface temperatures according to different reconstruction s from climate proxies, each smoothed on a decadal scale, with the instrumental temperature record overlaid in black. refer to caption and adjacent text NOAA graph of Global Annual Temperature Anomalies 1950?2012, showing the El Nino -Southern Oscillation refer to caption and image description Earth has been in radiative imbalance since at least the 1970s, where less energ y leaves the atmosphere than enters it. Most of this extra energy has been absor bed by the oceans.[34] It is very likely that human activities substantially con tributed to this increase in ocean heat content.[35] The Earth's average surface temperature rose by 0.74}0.18 C over the period 1906?20 05. 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). Th e urban heat island effect is very small, estimated to account for less than 0.0 02 C of warming per decade since 1900.[36] Temperatures in the lower troposphere h ave increased between 0.13 and 0.22 C (0.22 and 0.4 F) per decade since 1979, accord ing to satellite temperature measurements. Climate proxies show the temperature to have been relatively stable over the one or two thousand years before 1850, w ith regionally varying fluctuations such as the Medieval Warm Period and the Lit tle Ice Age.[37] The warming that is evident in the instrumental temperature record is consistent with a wide range of observations, as documented by many independent scientific groups.[38] Examples include sea level rise (water expands as it warms),[39] wi despread melting of snow and ice,[40] increased heat content of the oceans,[38] increased humidity,[38] and the earlier timing of spring events,[41] e.g., the f lowering of plants.[42] The probability that these changes could have occurred b y chance is virtually zero.[38] Recent estimates by NASA's Goddard Institute for Space Studies (GISS) and the Na tional Climatic Data Center show that 2005 and 2010 tied for the planet's warmes t year since reliable, widespread instrumental measurements became available in the late 19th century, exceeding 1998 by a few hundredths of a degree.[43][44][4 5] 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 d ifferences between these three years."[46] The World Meteorological Organization (WMO) 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 1 998 (+0.51 C), although the differences between the three years are not statistica lly significant..."[47] Every year from 1986 to 2013 has seen annual average glo bal land and ocean surface temperatures above the 1961-1990 average.[48][49] Temperatures in 1998 were unusually warm because global temperatures are affecte d by the El Nino-Southern Oscillation (ENSO), and the strongest El Nino in the p ast century occurred during that year.[50] Global temperature is subject to shor t-term fluctuations that overlay long term trends and can temporarily mask them.