global warming

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 20th cent., the atmospheric temperature rose 1.1°F (0.6°C), and sea level rose 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 2007 report by the Intergovernmental Panel on Climate Change, based on a three-year study, termed global warming "unequivocal" and said that most of the change was most likely due to human activities.

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. The United States, Australia, China, India, Japan, and South Korea established (2005) an agreement outside the Kyoto Protocal that proposed to reduce emissions through the development and implementation of new technologies. The Asia-Pacific Partnership on Clean Development and Climate, as it is called, involves no commitments on the part of its members; it held its first meeting in 2006. Also in 2006, California enacted legislation that called for cutting carbon dioxide emissions by 25% by 2020; the state is responsible for nearly 7% of all such emissions in the United States. In 2007 President George W. Bush called for the world's major polluting nations to set global and national goals for the reduction of greenhouse gas emissions, but the nonbinding nature of the proposed goals provoked skepticism from nations that favored stronger measures.

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); T. Flannery, The Weather Makers: How Man Is Changing the Climate and What It Means for Life on Earth (2006); E. Kolbert, Field Notes from a Catastrophe (2006); E. Linden, The Winds of Change (2006).

global warming ‘Global warming’ is the term applied to increasing average global temperature, popularly associated with the enhanced greenhouse effect. Since the mid-1980s, the prospect of warming has become reality. Global temperature series, combining observations from land and sea surface, have shown that temperatures have risen by between 0.5 and 0.8 °C over the past 100 years, the warmest year being 1998, followed by 1997, 1995, and 1999. This warming has coincided with advances in computer modelling of the enhanced greenhouse effect. This is the process by which long-wave (outgoing) radiation emitted from the surface of the Earth is absorbed by greenhouse gases, primarily carbon dioxide, methane, nitrous oxide, various chlorofluorocarbons, tropospheric ozone, and water vapour. The atmospheric life of greenhouse gases means that emissions in the late-twentieth century will still be making a contribution to the greenhouse effect at the end of the twenty-first century.

Climate modelling is an attempt to simulate the effects of changing atmospheric processes, including changes in the radiation balance caused by greenhouse gases. The equilibrium (eventual) response to a doubling of the pre-Industrial Revolution greenhouse effect is expected to result in a warming of 2–4 °C by the late twenty-first century.

Since the late 1980s, research has been focused through the Intergovernmental Panel on Climate Change (IPCC). The rate at which greenhouse gases concentrations will increase and the sensitivity of the climate system to such change are key uncertainties, together with various forms of positive and negative feedback (e.g. those associated with changes in cloud cover). In the early 1990s, transient (time-dependent) models started to incorporate more fully the thermal inertia of oceans, indicating possible rates of warming. These indicate an average warming of 1 to 1.4 °C by about 2040. This is likely to be exceeded in the interiors of the larger continents (especially in winter at high latitudes), whilst some sea surfaces and adjacent coastal regions may have little or no warming.

The uncertain outcome and consequences of climate change in the twenty-first century accounts for the urgency of securing international policy responses. The Climate Convention signed after the 1992 Earth Summit require signatories to reduce greenhouse gas emissions to 1990 levels by 2000, with further reductions being sought by 1997. We are, however, still likely to have committed the Earth to a warming over the next 50 years two to three times that of the last 150 years. Additional uncertainty arises from the response to warming of other components of the climate system, notably any changes of the atmospheric circulation on the distribution of rainfall (see recent climate changes). Global warming can thus be seen as one of the most far-reaching environmental problems of our time.

Julian Mayes

Bibliography

Ferguson, H. L. and Jager, J. (eds) (1991) Climate change: science, impacts and policy. Proceedings of the 2nd World Climate Conference. Cambridge University Press.
Houghton, J. T., Jenkins, G. T., and Ephraums, J. J. (eds) (1990) Climate change: the IPPC scientific assessment. Cambridge University Press.
Houghton, J. T., Callander, B. A., and Varney, S. K. (eds) (1992) Climate change 1992: the supplementary report to the IPPC scientific assessment. Cambridge University Press.
Watson, R. T., Zinyowera, M. C., and Moss, R. H. (eds) (1996) Climate change 1995. Impacts, adaptations and mitigation of climate change: scientific–technical anlayses. Contribution of Working Group II to the (2nd) Assessment Report of the Intergovernment Panel on Climate Change. Cambridge University Press.
Parry, M. L. (ed.) (1991) The potential effects of climate change in the United Kingdom. UK Climate Change Impacts Review Group, 1st Report. HMSO, Norwich.

global warming The modification of climates that would result from the retention of an increased proportion of terrestrial radiation by certain atmospheric gases emitted mainly as by-products of human activities (i.e. an anthropogenically induced ‘greenhouse effect’). Computer models of the general circulation predict that the warming would occur mainly in middle to high latitudes, but its precise extent and consequences (e.g. in terms of changes in sea level) are uncertain.