Global Warming(Encyclopedia)
global warming, the gradual increase of the temperature of the earth's lower atmosphere as a result of the increase in greenhouse gases since the Industrial Revolution.
The temperature of the atmosphere near the earth's surface is warmed through a natural process called the greenhouse effect. Visible, shortwave light comes from the sun to the earth, passing unimpeded through a blanket of thermal, or greenhouse, gases composed largely of water vapor, carbon dioxide, methane, nitrous oxide, and ozone. Infrared radiation reflects off the planet's surface toward space but does not easily pass through the thermal blanket. Some of it is trapped and reflected downward, keeping the planet at an average temperature suitable to life, about 60°F (16°C).
Growth in industry, agriculture, and transportation since the Industrial Revolution has produced additional quantities of the natural greenhouse gases plus chlorofluorocarbons and other gases, augmenting the thermal blanket. It is generally accepted that this increase in the quantity of greenhouse gases is trapping more heat and increasing global temperatures, making a process that has been beneficial to life potentially disruptive and harmful. During the past century, the atmospheric temperature has risen 1.1°F (0.6°C), and sea level has risen several inches. Some projected, longer-term results of global warming include melting of polar ice, with a resulting rise in sea level and coastal flooding; disruption of drinking water supplies dependent on snow melts; profound changes in agriculture due to climate change; extinction of species as ecological niches disappear; more frequent tropical storms; and an increased incidence of tropical diseases.
Among factors that may be contributing to global warming are the burning of coal and petroleum products (sources of carbon dioxide, methane, nitrous oxide, ozone); deforestation, which increases the amount of carbon dioxide in the atmosphere; methane gas released in animal waste; and increased cattle production, which contributes to deforestation, methane production, and use of fossil fuels.
Much of the debate surrounding global warming has centered on the accuracy of scientific predictions concerning future warming. To predict global climatic trends, climatologists accumulate large historical databases and use them to create computerized models that simulate the earth's climate. The validity of these models has been a subject of controversy. Skeptics say that the climate is too complicated to be accurately modeled, and that there are too many unknowns. Some also question whether the observed climate changes might simply represent normal fluctuations in global temperature. Nonetheless, for some time there has been general agreement that at least part of the observed warming is the result of human activity, and that the problem needs to be addressed. In 1992, at the United Nations Conference on Environment and Development, over 150 nations signed a binding declaration on the need to reduce global warming.
In 1994, however, a UN scientific advisory panel, the Intergovernmental Panel on Climate Change, concluded that reductions beyond those envisioned by the treaty would be needed to avoid global warming. The following year, the advisory panel forecast a rise in global temperature of from 1.44 to 6.3°F (0.8–3.5°C) by 2100 if no action is taken to cut down on the production of greenhouse gases, and a rise of from 1 to 3.6°F (0.5–2°C) even if action is taken (because of already released gases that will persist in the atmosphere).
A UN Conference on Climate Change, held in Kyoto, Japan, in 1997 resulted in an international agreement to fight global warming, which called for reductions in emissions of greenhouse gases by industrialized nations. Not all industrial countries, however, immediately signed or ratified the accord. In 2001 the G. W. Bush administration announced it would abandon the Kyoto Protocol; because the United States produces about one quarter of the world's greenhouse gases, this was regarded as a severe blow to the effort to slow global warming. Despite the American move, most other nations agreed later in the year (in Bonn, Germany, and in Marrakech, Morocco) on the details necessary to convert the agreement into a binding international treaty, which came into force in 2005 after ratification by more than 125 nations.
Improved automobile mileage, reforestation projects, energy efficiency in construction, and national support for mass transit are among relatively simpler adjustments that could significantly lower U.S. production of greenhouse gases. More aggressive adjustments include a gradual worldwide shift away from the use of fossil fuels, the elimination of chlorofluorocarbons, and the slowing of deforestation by restructuring the economies of developing nations. In 2002 the Bush administration proposed several voluntary measures for slowing the increase in, instead of reducing, emissions of greenhouses gases.
Bibliography
See P. Brown, Global Warming: Can Civilization Survive? (1997); T. G. Moore, Climate of Fear: Why We Shouldn't Worry about Global Warming (1998); S. G. Philander, Is the Temperature Rising?: The Uncertain Science of Global Warming (1998); K. E. Ready, GAIA Weeps: The Crisis of Global Warming (1998); G. E. Christianson, Greenhouse: The 200-Year Story of Global Warming (1999).
Global WarmingResearch, Policy and Education The Earth Institute at Columbia U.www.earthinstitute.columbia.edu
ancient astronomy & mythnew views on ancient science read: Origin of Culturewww.crimsonbird.com
Science
global warming
The term attached to the notion that the Earth's temperature is increasing due to the greenhouse effect.
Whether global warming is actually happening is a subject of scientific debate.
Potential effects
Many public policy organizations, governments, and individuals are concerned that global warming could harm the environment in various ways. As well as the intrinsic value attached by them to the preservation of the environment, there are wide range of possible consequences for humans. These include rising sea levels, declining output of global agriculture, increased extreme weather, and the spread of disease.
The extent and likelihood of these consequences is a matter of considerable controversy, with environmentalist groups typically emphasizing the possible dangers and groups close to industry questioning the climate models and consequences of global warming — and funding scientists to do so. A summary of possible effects and our current understanding can be found in the report of the IPCC Working Group II. Much remains to be learned, however.
Effects on ecosystems
Secondary evidence of global warming — lessened snow cover, rising sea levels, weather changes — provides examples of consequences of global warming that may influence not only human activities but also the ecosystems. Increasing global temperature means that ecosystems may
change; some species may be forced out of their habitats (possibly to extinction) because of changing conditions, while others may flourish. Few of the terrestrial ecoregions on Earth could expect to be unaffected.Sea level rise
Main article: sea level rise
Another effect of great concern is a sea level rise. Sea levels appear to be rising 1 to 2 mm/y this century, although satellite data show a rate of 3 mm/y since 1992. Some Pacific Ocean island nations, such as Tuvalu, are concerned about the possibility of an eventual evacuation. For historical reasons to do with trade, many of the world's largest and most prosperous cities are on the coast, and the cost of building better coastal defenses is likely to be considerable. Some countries will be more affected than others - low-lying countries such as Bangladesh and the Netherlands will be worst hit by any sea level rise, in terms of floods or the cost of preventing them.
More extreme weather
Increasing water vapor at Boulder, Colorado.
As the climate grows warmer, evaporation will increase. This will cause heavier rainfall and more erosion. Many scientists think that it could result in more extreme weather as global warming progresses. The IPCC TAR says: "...global average water vapour concentration and precipitation are projected to increase during the 21st century. By the second half of the 21st century, it is likely that precipitation will have increased over northern mid- to high latitudes and Antarctica in winter. At low latitudes there are both regional increases and decreases over land areas. Larger year to year variations in precipitation are very likely over most areas where an increase in mean precipitation is projected" .
Decline of agriculture
Main article: Global warming and agriculture
For some time it was hoped that a positive effect of global warming would be increased agricultural yields, because of the role of CO2 in photosynthesis. This may still be true in some regions (such as Siberia), but recent evidence is that global yields will be negatively affected. "Rising atmospheric temperatures, longer droughts and side-effects of both, such as higher levels of ground-level ozone gas, are likely to bring about a substantial reduction in crop yields in the coming decades, large-scale experiments have shown."
Spread of disease
It has been claimed that global warming will probably extend the favourable zones for vectors conveying infectious disease such as malaria. However, it has been pointed out that despite the disappearance of infectious disease most temperate regions, the indigenous mosquitoes that transmitted it were never eliminated and remain common in some areas. Thus, although temperature is important in the transmission dynamics of malaria, many other variables are of equal or greater importance. (http://www.cdc.gov/ncidod/eid/vol6no1/reiter.htm)
Destabilisation of local climates
Global warming might also have other, less obvious effects. The North Atlantic drift, for instance, is affected by salinity changes. It seems that it is diminishing as the climate grows warmer, and there has been speculation that areas like Scandinavia and Britain that are warmed by the drift might face a colder climate in spite of the general global warming. Some even fear that global warming may be able to trigger the type of abrupt massive temperature shifts which bracketed the Younger Dryas period. (See the discussion of chaos theory for related ideas.). However, in coupled AOGCMs the warming effects outweigh the cooling, even locally: the IPCC TAR notes that even in models where the THC weakens, there is still a warming over Europe. (http://www.grida.no/climate/ipcc_tar/wg1/357.htm). See also ([www.realclimate.org]).
A study (published in Science) of changes to Siberia's permafrost suggests that it is gradually disappearing in the southern regions, leading to the loss of nearly 11% of Siberia's nearly 11,000 lakes since 1971.[41] (http://www.guardian.co.uk/international/story/0,,1503170,00.html)
Reducing ozone layer
One of the lesser-known effects of global warming is a reduction in the thickness of the ozone layer, which protects life on Earth from harmful radiation. Global warming appears to be partially countering the improvements in the ozone layer caused by the reduction in the use of ozone-destroying chemicals achieved through the Montreal Protocol. "What appears to have caused the further loss of ozone is the increasing number of stratospheric clouds in the winter, 15 miles above the earth. These clouds, in the middle of the ozone layer, provide a platform which makes it easier for rapid chemical reactions which destroy ozone to take place." ([www.guardian.co.uk]) A reduced ozone layer has negative impacts on human health (notably skin cancer and eye problems such as cataracts) and on ecosystems. However, the net effect of the thinning of the ozone layer on human health may be positive. Research by Dr. Edward Giovannucci, a Harvard University professor of medicine and nutrition who gave a keynote lecture at a recent American Association for Cancer Research, suggests that vitamin D might help prevent 30 deaths for each one caused by skin cancer. Vitamin D is nicknamed the "sunshine vitamin" because the skin makes it from ultraviolet rays. ([www.freenewmexican.com]) (http://www.cbsnews.com/stories/2005/02/01/health/main670995.shtml) The ecological impact may have further knock-on effects, as it reduces photosynthesis in plants (with potential impacts on agriculture) and damages the DNA of plankton, which play a significant role in the world's carbon cycle. On the technical details of the two-way interaction between the ozone layer and global warming, see the relation of global warming and ozone depletion, below.
Possible positive effects
However, global warming may also have positive effects, since higher temperatures and higher CO2 concentrations may improve ecosystems' productivity. Satellite data shows that the
productivity of the Northern Hemisphere has increased since 1982. On the other hand, an increase in the total amount of biomass produced is not necessarily all good, since biodiversity can still decrease even though a smaller number of species are flourishing. Similarly, from the human economic viewpoint, an increase in total biomass but a decrease in crop harvests would be a net disadvantage. In addition, IPCC models predict that higher CO2 concentrations would only spur growth of flora up to a point, because in many regions the limiting factors are water or nutrients, not temperature or CO2; after that, though greenhouse effects and warming would continue there would be no compensatory increase in growth.A possible counter-argument to this is the claim that suppression of plant growth is caused by a shortage of atmospheric carbon dioxide, which is rare in comparison to oxygen (21%). This carbon dioxide starvation becomes apparent in photorespiration, where there is so little carbon dioxide, that oxygen can enter a plant's chloroplasts and takes the place where carbon dioxide normally would be in the Calvin Cycle. This causes the sugars being made to be destroyed, badly suppressing growth.
The relation between global warming and ozone depletion
Main article: ozone depletion
Although they are often interlinked in the popular press, the connection between global warming and ozone depletion is not strong. There are four areas of linkage:
Global warming from CO2 radiative forcing is expected (perhaps somewhat surprisingly) to cool the stratosphere. This, in turn, would lead to a relative increase in ozone depletion and the frequency of ozone holes.
Conversely, ozone depletion represents a radiative forcing of the climate system. There are two opposed effects: reduced ozone allows more solar radiation to penetrate, thus warming the troposphere. But a colder stratosphere emits less long-wave radiation, tending to cool the troposphere. Overall, the cooling dominates: the IPCC concludes that observed stratospheric O3 losses over the past two decades have caused a negative forcing of the surface-troposphere system of about –0.15 ± 0.10 W m–2 .
One of the strongest predictions of the GW theory is that the stratosphere should cool. However, although this is observed, it is difficult to use it for attribution (for example, warming induced by increased solar radiation would not have this upper cooling effect) because similar cooling is caused by ozone depletion.
Ozone depleting chemicals are also greenhouse gases, representing 0.34 ± 0.03 W/m2, or about 14% of the total radiative forcing from well-mixed GHG's .
The relation between global warming and global dimming
Main article: global dimming
Some scientists now consider that the effects of the recently recognized phenomenon of global dimming (the reduction in sunlight reaching the surface of the planet, possibly due to aerosols) may have masked some of the effect of global warming. If this is so, the indirect aerosol effect is stronger than previously believed, which would imply that the climate sensitivity to CO2 is also stronger. Concerns about the effect of aerosol on the global climate were first researched as part of concerns over global cooling in the 1970s.
Attempts to combat global warming
Mitigating temperature rise
Kyoto Protocol
Carbon sequestration / Carbon tax
Future energy development
Soft energy path
United Kingdom Climate Change Programme
Mitigating the effects of global warming
