Global warming and climate change are terms for the observed century-scale rise in the average temperature of the Earth’s climate system and its related effects. Multiple lines of scientific evidence show that the climate system is warming. Although the increase of near-surface atmospheric temperature is the measure of global warming often reported in the popular press, most of the additional energy stored in the climate system since 1970 has gone into ocean warming. The remainder has melted ice and warmed the continents and atmosphere.[a] Many of the observed changes since the 1950s are unprecedented over tens to thousands of years. On 12 November 2015, NASA scientists reported that human-made carbon dioxide (CO2) continues to increase above levels not seen in hundreds of thousands of years: currently, about half of the carbon dioxide released from the burning of fossil fuels is not absorbed by vegetation and the oceans and remains in the atmosphere.
Scientific understanding of global warming is increasing. The Intergovernmental Panel on Climate Change (IPCC) reported in 2014 that scientists were more than 95% certain that global warming is mostly being caused by increasing concentrations of greenhouse gases (GHG) and other human (anthropogenic) activities. Climate model projections summarized in the report indicated that during the 21st century the global surface temperature is likely to rise a further 0.3 to 1.7 °C (0.5 to 3.1 °F) for their lowest emissions scenario using stringent mitigation and 2.6 to 4.8 °C (4.7 to 8.6 °F) for their highest. These findings have been recognized by the national science academies of the major industrialized nations[b] and are not disputed by any scientific body of national or international standing.
Future climate change and associated impacts will differ from region to region around the globe. Anticipated effects include warming global temperature, rising sea levels, changing precipitation, and expansion of deserts in the subtropics. Warming is expected to be greater over land than over the oceans and greatest in the Arctic, with the continuing retreat of glaciers, permafrost and sea ice. Other likely changes include more frequent extreme weather events including heat waves, droughts, heavy rainfall with floods and heavy snowfall; ocean acidification; and species extinctions due to shifting temperature regimes. Effects significant to humans include the threat to food security from decreasing crop yields and the abandonment of populated areas due to rising sea levels. Because the climate system has a large inertia and CO2 will stay in the athmosphere for a long time, many of these effects will not only exist for decades or centuries, but will persist for tens of thousands of years.
Possible societal responses to global warming include mitigation by emissions reduction, adaptation to its effects, building systems resilient to its effects, and possible future climate engineering. Most countries are parties to the United Nations Framework Convention on Climate Change (UNFCCC), whose ultimate objective is to prevent dangerous anthropogenic climate change. The UNFCCC have adopted a range of policies designed to reduce greenhouse gas emissions and to assist in adaptation to global warming. Parties to the UNFCCC have agreed that deep cuts in emissions are required, and that future global warming should be limited to below 2.0 °C (3.6 °F) relative to the pre-industrial level.[c]
Public reactions to global warming and general fears of its effects are also steadily on the rise, with a global 2015 Pew Research Center report showing a median of 54% who consider it “a very serious problem”. There are, however, significant regional differences. Notably, Americans and Chinese, whose economies are responsible for the greatest annual CO2 emissions, are among the least concerned.
- Scientific journals use “global warming” to describe an increasing global average temperature just at earth’s surface, and most of these authorities further limit “global warming” to such increases caused by human activities or increasing greenhouse gases.
- The 2001 joint statement was signed by the national academies of science of Australia, Belgium, Brazil, Canada, the Caribbean, the People’s Republic of China, France, Germany, India, Indonesia, Ireland, Italy, Malaysia, New Zealand, Sweden, and the UK. The 2005 statement added Japan, Russia, and the U.S. The 2007 statement added Mexico and South Africa. The Network of African Science Academies, and the Polish Academy of Sciences have issued separate statements. Professional scientific societies include American Astronomical Society, American Chemical Society, American Geophysical Union, American Institute of Physics, American Meteorological Society, American Physical Society, American Quaternary Association, Australian Meteorological and Oceanographic Society, Canadian Foundation for Climate and Atmospheric Sciences, Canadian Meteorological and Oceanographic Society, European Academy of Sciences and Arts, European Geosciences Union, European Science Foundation, Geological Society of America, Geological Society of Australia, Geological Society of London-Stratigraphy Commission,InterAcademy Council, International Union of Geodesy and Geophysics, International Union for Quaternary Research, National Association of Geoscience Teachers, National Research Council (US), Royal Meteorological Society, and World Meteorological Organization.
- Earth has already experienced almost 1/2 of the 2.0 °C (3.6 °F) described in the Cancún Agreement. In the last 100 years, Earth’s average surface temperature increased by about 0.8 °C (1.4 °F) with about two thirds of the increase occurring over just the last three decades.
- The greenhouse effect produces an average worldwide temperature increase of about 33 °C (59 °F) compared to black body predictions without the greenhouse effect, not an average surface temperature of 33 °C (91 °F). The average worldwide surface temperature is about 14 °C (57 °F).
- A rise in temperature from 10 °C to 20 °C is not a doubling of absolute temperature; a rise from (273 + 10) K = 283 K to (273 + 20) K = 293 K is an increase of (293 − 283)/283 = 3.5 %.
- 16 January 2015: NASA GISS: NASA GISS: NASA, NOAA Find 2014 Warmest Year in Modern Record, in: Research News. NASA Goddard Institute for Space Studies, New York, NY, USA. Retrieved 20 February 2015
- Gillis, Justin (28 November 2015). “Short Answers to Hard Questions About Climate Change”. The New York Times. Retrieved 29 November 2015.
- Hartmann, D. L.; Klein Tank, A. M. G.; Rusticucci, M. (2013).”2: Observations: Atmosphere and Surface” (PDF). IPCC WGI AR5 (Report). p. 198.
Evidence for a warming world comes from multiple independent climate indicators, from high up in the atmosphere to the depths of the oceans. They include changes in surface, atmospheric and oceanic temperatures; glaciers; snow cover; sea ice; sea level and atmospheric water vapour. Scientists from all over the world have independently verified this evidence many times.
- “Myth vs Facts….”. EPA (US). 2013.The U.S. Global Change Research Program, the National Academy of Sciences, and the Intergovernmental Panel on Climate Change (IPCC) have each independently concluded that warming of the climate system in recent decades is ‘unequivocal’. This conclusion is not drawn from any one source of data but is based on multiple lines of evidence, including three worldwide temperature datasets showing nearly identical warming trends as well as numerous other independent indicators of global warming (e.g., rising sea levels, shrinking Arctic sea ice).
- Borenstein, Seth (29 November 2015). “Earth is a wilder, warmer place since last climate deal made”. Retrieved29 November 2015.
- Rhein, M.; Rintoul, S. R. (2013). “3: Observations: Ocean”(PDF). IPCC WGI AR5 (Report). p. 257.
Ocean warming dominates the global energy change inventory. Warming of the ocean accounts for about 93% of the increase in the Earth’s energy inventory between 1971 and 2010 (high confidence), with warming of the upper (0 to 700 m) ocean accounting for about 64% of the total. Melting ice (including Arctic sea ice, ice sheets and glaciers) and warming of the continents and atmosphere account for the remainder of the change in energy.
- IPCC, Climate Change 2013: The Physical Science Basis – Summary for Policymakers, Observed Changes in the Climate System, p. 2, in IPCC AR5 WG1 2013. “Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia.”
- a b Buis, Alan; Ramsayer, Kate; Rasmussen, Carol (12 November 2015). “A Breathing Planet, Off Balance”. NASA. Retrieved 13 November 2015.
- a b Staff (12 November 2015). “Audio (66:01) – NASA News Conference – Carbon & Climate Telecon”. NASA. Retrieved12 November 2015.
- a b St. Fleur, Nicholas (10 November 2015). “Atmospheric Greenhouse Gas Levels Hit Record, Report Says”. The New York Times. Retrieved 11 November 2015.
- a b Ritter, Karl (9 November 2015). “UK: In 1st, global temps average could be 1 degree C higher”. AP News. Retrieved11 November 2015.
- a b “CLIMATE CHANGE 2014: Synthesis Report. Summary for Policymakers” (PDF). IPCC. Retrieved 1 November2015.
The following terms have been used to indicate the assessed likelihood of an outcome or a result: virtually certain 99–100% probability, very likely 90–100%, likely 66–100%, about as likely as not 33–66%, unlikely 0–33%, very unlikely 0–10%, exceptionally unlikely 0–1%. Additional terms (extremely likely: 95–100%, more likely than not >50–100%, more unlikely than likely 0–<50% and extremely unlikely 0–5%) may also be used when appropriate.
- “CLIMATE CHANGE 2014: Synthesis Report. Summary for Policymakers” (PDF). IPCC. Retrieved 7 March2015.
The evidence for human influence on the climate system has grown since the Fourth Assessment Report (AR4). It is extremely likely that more than half of the observed increase in global average surface temperature from 1951 to 2010 was caused by the anthropogenic increase in greenhouse gas concentrations and other anthropogenic forcings together
- America’s Climate Choices: Panel on Advancing the Science of Climate Change; National Research Council (2010). Advancing the Science of Climate Change. Washington, D.C.: The National Academies Press. ISBN 0-309-14588-0.
(p1) … there is a strong, credible body of evidence, based on multiple lines of research, documenting that climate is changing and that these changes are in large part caused by human activities. While much remains to be learned, the core phenomenon, scientific questions, and hypotheses have been examined thoroughly and have stood firm in the face of serious scientific debate and careful evaluation of alternative explanations. * * * (p21-22) Some scientific conclusions or theories have been so thoroughly examined and tested, and supported by so many independent observations and results, that their likelihood of subsequently being found to be wrong is vanishingly small. Such conclusions and theories are then regarded as settled facts. This is the case for the conclusions that the Earth system is warming and that much of this warming is very likely due to human activities.
- Stocker et al., Technical Summary, in IPCC AR5 WG1 2013.
- “Joint Science Academies’ Statement” (PDF). Retrieved6 January 2014.
- Kirby, Alex (17 May 2001). “Science academies back Kyoto”. BBC News. Retrieved 27 July 2011.
- a b DiMento, Joseph F. C.; Doughman, Pamela M. (2007).Climate Change: What It Means for Us, Our Children, and Our Grandchildren. The MIT Press. p. 68. ISBN 978-0-262-54193-0.
- Parry, M.L.; et al., “Technical summary”, Box TS.6. The main projected impacts for regions, in IPCC AR4 WG2 2007, pp. 59–63
- Solomon et al., Technical Summary, Section TS.5.3: Regional-Scale Projections, in IPCC AR4 WG1 2007.
- Lu, Jian; Vechhi, Gabriel A.; Reichler, Thomas (2007).”Expansion of the Hadley cell under global warming” (PDF).Geophysical Research Letters 34 (6): L06805.Bibcode:2007GeoRL..3406805L.doi:10.1029/2006GL028443.
- On snowfall:
- Christopher Joyce (15 February 2010). “Get This: Warming Planet Can Mean More Snow”. NPR.
- “Global warming means more snowstorms: scientists”. 1 March 2011.
- “Does record snowfall disprove global warming?”. 9 July 2010. Retrieved 14 December 2014.
- Battisti, David; Naylor, Rosamund L. (2009). “Historical warnings of future food insecurity with unprecedented seasonal heat”. Science 323 (5911): 240–4.doi:10.1126/science.1164363. PMID 19131626. Retrieved13 April 2012.
- US NRC 2012, p. 26
- Peter U. Clark et al.: Consequences of twenty-first-century policy for multi-millennial climate and sea-level change. Nature Climate Change 6, 2016, 360-369, doi:10.1038/NCLIMATE2923
- United Nations Framework Convention on Climate Change(UNFCCC) (2011). “Status of Ratification of the Convention”. UNFCCC Secretariat: Bonn, Germany: UNFCCC.. Most countries in the world are Parties to the United Nations Framework Convention on Climate Change (UNFCCC), which has adopted the 2 °C target. As of 25 November 2011, there are 195 parties (194 states and 1 regional economic integration organization (theEuropean Union)) to the UNFCCC.
- “Article 2”. The United Nations Framework Convention on Climate Change.
The ultimate objective of this Convention and any related legal instruments that the Conference of the Parties may adopt is to achieve, in accordance with the relevant provisions of the Convention, stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system. Such a level should be achieved within a time-frame sufficient to allow ecosystems to adapt naturally to climate change, to ensure that food production is not threatened and to enable economic development to proceed in a sustainable manner. Such a level should be achieved within a time-frame sufficient to allow ecosystems to adapt naturally to climate change, to ensure that food production is not threatened and to enable economic development to proceed in a sustainable manner, excerpt from the founding international treaty that took force on 21 March 1994.
- a b United Nations Framework Convention on Climate Change(UNFCCC) (2005). “Sixth compilation and synthesis of initial national communications from Parties not included in Annex I to the Convention. Note by the secretariat. Executive summary”(PDF). Geneva (Switzerland): United Nations Office at Geneva.
- Gupta, S. et al. 13.2 Climate change and other related policies, in IPCC AR4 WG3 2007.
- Ch 4: Climate change and the energy outlook., in IEA 2009, pp. 173–184 (pp.175-186 of PDF)
- a b United Nations Framework Convention on Climate Change(UNFCCC) (2011). “Compilation and synthesis of fifth national communications. Executive summary. Note by the secretariat”(PDF). Geneva (Switzerland): United Nations Office at Geneva.
- Adger, et al., Chapter 17: Assessment of adaptation practices, options, constraints and capacity, Executive summary, inIPCC AR4 WG2 2007.
- 6. Generating the funding needed for mitigation and adaptation (PDF), in “World Development Report 2010: Development and Climate Change”. Washington, D.C., USA: The International Bank for Reconstruction and Development / The World Bank. 2010: 262–263.
- a b United Nations Framework Convention on Climate Change(UNFCCC) (2011). “Conference of the Parties – Sixteenth Session: Decision 1/CP.16: The Cancun Agreements: Outcome of the work of the Ad Hoc Working Group on Long-term Cooperative Action under the Convention (English): Paragraph 4” (PDF). UNFCCC Secretariat: Bonn, Germany: UNFCCC: 3.“(…) deep cuts in global greenhouse gas emissions are required according to science, and as documented in the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, with a view to reducing global greenhouse gas emissions so as to hold the increase in global average temperature below 2 °C above preindustrial levels”
- America’s Climate Choices. Washington, D.C.: The National Academies Press. 2011. p. 15. ISBN 978-0-309-14585-5.
The average temperature of the Earth’s surface increased by about 1.4 °F (0.8 °C) over the past 100 years, with about 1.0 °F (0.6 °C) of this warming occurring over just the past three decades.