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. Global warming and its effects are also referred to as climate change.
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 smaller quantities of chlorofluorocarbons and other more potent greenhouse 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 increase in 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 (IPCC), 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 IPCC report, based on a three-year study, termed global warming "unequivocal" and said that most of the change was most likely due to human activities, and its report five years later restated those findings even more strongly.
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, known as the Kyoto Protocol. In 2001 the G. W. Bush administration announced it would abandon the accord; 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.
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 created (2005) an agreement outside the Kyoto Protocol that proposed to reduce emissions through the development and implementation of new technologies. The Asia-Pacific Partnership on Clean Development and Climate established 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 U.S. President 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. The 15th UN Conference on Climate Change, held in Copenhagen, Denmark, in Dec., 2009, failed to lead to a legally binding treaty on reducing global greenhouse-gas emissions. It had been hoped that the meeting would result in a new protocol that would replace that agreed to at Kyoto. The 17th conference, which met in 2012 in Durban, South Africa, agreed to extend the accord (which was extended to 2020 later in 2012) and also agreed to work toward an unspecified new accord; at the same time, however, Canada became the first ratifying nation to withdraw from the Kyoto Protocol.
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); P. Conkling et al., The Fate of Greenland: Lessons from Abrupt Climate Change (2011); B. McKibben, ed., The Global Warming Reader (2012).
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