is the increase in the average temperature of the Earth's near-surface air and oceans since the mid-twentieth century and its projected continuation. Global surface temperature increased 0.74 ± 0.18 °C (1.33 ± 0.32 °F) during the last century.[1][A] The Intergovernmental Panel on Climate Change (IPCC) concludes that anthropogenic greenhouse gases are responsible for most of the observed temperature increase since the middle of the twentieth century,[1] and that natural phenomena such as solar variation and volcanoes probably had a small warming effect from pre-industrial times to 1950 and a small cooling effect afterward.[2][3] These basic conclusions have been endorsed by more than 40 scientific societies and academies of science,[B] including all of the national academies of science of the major industrialized countries
GreenHouse gases
The greenhouse effect was discovered by Joseph Fourier in 1824 and first investigated quantitatively by Svante Arrhenius in 1896.[14] It is the process by which absorption and emission of infrared radiation by atmospheric gases warm a planet's lower atmosphere and surface. 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 atmospheric concentrations of greenhouse gases.
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, and adaptation to the changing global environment.
Mitigation
Emissions reduction
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.[88] Only the United States and Kazakhstan have not ratified the treaty, with the United States historically being the world's largest emitter of greenhouse gases. The treaty expires in 2012. International talks began in May 2007 on a future treaty to succeed the current one.[89] UN negotiations are now gathering pace in advance of a key meeting in Copenhagen in December 2009.
Geoengineering
Geoengineering is the deliberate modification of Earth's natural environment on a large scale to suit human needs.[95] An example is greenhouse gas remediation, which removes greenhouse gases from the atmosphere, usually through carbon sequestration techniques such as carbon dioxide air capture.[96] Solar radiation management reduces insolation, such as by the addition of stratospheric sulfur aerosols.
Adaptation
A wide variety of measures have been suggested for adaptation to global warming. These range from the trivial, such as the installation of air-conditioning equipment, up to major infrastructure projects, such as abandonment of settlements threatened by sea level rise. Measures including water conservation,[98] changes to agricultural practices,[99] construction of flood defences,[100] changes to medical care,[101] and interventions to protect threatened species[102] 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.
