Global warming

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. According to United Nations Environment Programme (UNEP), economic sectors likely to face difficulties related to climate change include banks, agriculture, transport and others. The broad agreement among climate scientists that global temperatures will continue to increase has led some nations, states, corporations and individuals to implement responses. 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. 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. A positive feedback is a process that amplifies some change.

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. 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 CO2, methane, tropospheric ozone, CFCs and nitrous oxide.

The 2007 IPCC Fourth Assessment Report concludes that no one technology or sector can be completely responsible for mitigating future warming. Since 1979, land temperatures have increased about twice as fast as ocean temperatures (0.25 °C per decade against 0.13 °C per decade). 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.

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. Some effects on both the natural environment and human life are, at least in part, already being attributed to global warming.

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). 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. Debates weigh the benefits of limiting industrial emissions of greenhouse gases against the costs that such changes would entail. Some global warming skeptics in the science or political community 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 on the magnitude of the threat posed by global warming.

Atmospheric soot aerosols directly absorb solar radiation, which heats the atmosphere and cools the surface. 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. The main tools for projecting future climate changes are mathematical models based on physical principles including fluid dynamics, thermodynamics and radiative transfer.

Australia announced its Carbon Pollution Reduction Scheme in 2008. 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. 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.

The future rate of rise will depend on uncertain economic, sociological, technological, and natural developments. Most national governments have signed and ratified the Kyoto Protocol aimed at reducing greenhouse gas emissions. The most commonly discussed measure of global warming is the trend in globally averaged temperature near the Earth s surface.

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. Temperature changes vary over the globe. 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.

Over a third of the world s population were unaware of global warming, developing countries less aware than developed, and Africa the least aware. Reduction of stratospheric ozone has a cooling influence, but substantial ozone depletion did not occur until the late 1970s. 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. In addition to their direct effect by scattering and absorbing solar radiation, aerosols have indirect effects on the radiation budget. Soot may cool or warm, depending on whether it is airborne or deposited.

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 continuing retreat of glaciers, permafrost and sea ice is expected, with warming being strongest in the Arctic.

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. A wide variety of measures have been suggested for adaptation to global warming. Awareness does not equate to belief that global warming is a result of human activities.

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. The main positive feedback in global warming involves the tendency of warming to increase the amount of water vapor in the atmosphere.

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. 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.

No large-scale geoengineering projects have yet been undertaken. Increased publicity of the scientific findings surrounding global warming has resulted in political and economic debate. In 2007-2008 the Gallup Polls surveyed 127 countries. Broader effects are expected to include glacial retreat, Arctic shrinkage, and worldwide sea level rise.

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. Some models also include treatments of chemical and biological processes. 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).

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. 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 observational studies also show a positive feedback. 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. Temperate regions are projected to experience some benefits, such as fewer cold-related deaths. Additional anticipated effects include sea level rise of 0.18 to 0.59 meters (0.59 to 1.9 ft) in 2090-2100 relative to 1980-1999, The IPCC reports the aggregate net economic costs of damages from climate change globally (discounted to the specified year).

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. 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. External forcing is a term used in climate science for processes external to the climate system (though not necessarily external to Earth).

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. The concentrations of CO2 and methane have increased by 36% and 148% respectively since the mid-1700s. CO2 concentrations are continuing to rise due to burning of fossil fuels and land-use change.

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. Social and economic effects of global warming may be exacerbated by growing population densities in affected areas. 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. It usually is impossible to connect specific weather events to global warming.

Regionally (but not globally), as much as 50% of surface warming due to greenhouse gases may be masked by atmospheric brown clouds. Variations in solar output have been the cause of past climate changes. Greenhouse gases and solar forcing affect temperatures in different ways. Expressed as a linear trend, this temperature rose by 0.74°C ±0.18°C over the period 1906-2005.

It was discovered by Joseph Fourier in 1824 and was first investigated quantitatively by Svante Arrhenius in 1896. Attribution of recent climate change focuses on the first three types of forcing.

All modern climate models are in fact combinations of models for different parts of the Earth. Global surface temperature increased 0.74 ± 0.18 °C (1.33 ± 0.32 °F) during the last century. Climate model projections summarized in the latest IPCC report indicate that the global surface temperature will probably rise a further 1.1 to 6.4 °C (2.0 to 11.5 °F) during the twenty-first century. 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 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). 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, Geoengineering is the deliberate modification of Earth s natural environment on a large scale to suit human needs.

Prominent global warming skeptics include Richard Lindzen, Fred Singer, Patrick Michaels, John Christy, and Robert Balling. Find more about Global warming on Wikipedia s sister projects: Research Educational Albedo · Bond events · Cloud forcing · Glaciation · Global cooling · Ocean variability (AMO · ENSO · IOD · PDO) · Orbital variations · Orbital forcing · Radiative forcing · Solar variation · Volcanism . 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.

In 2005, the average social cost of carbon from 100 peer-reviewed estimates is US$12 per tonne of CO2, but range -$3 to $95/tCO2. Models suggest that mitigation can quickly begin to slow global warming, but that temperatures will appreciably decrease only after several centuries. Many environmental groups encourage individual action against global warming, as well as community and regional actions.

The urban heat island effect is estimated to account for about 0.002 °C of warming per decade since 1900. 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.

Accordingly, the IPCC Special Report on Emissions Scenarios gives a wide range of future CO2 scenarios, ranging from 541 to 970 ppm by the year 2100. The destruction of stratospheric ozone by chlorofluorocarbons is sometimes mentioned in relation to global warming. Others have suggested a quota on worldwide fossil fuel production, citing a direct link between fossil fuel production and CO2 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 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. 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 of global warming is accomplished through reductions in the rate of anthropogenic greenhouse gas release.

Although there are a few areas of linkage, the relationship between the two is not strong.