. . . Excerpted from
       EARTH '88: CHANGING GEOGRAPHIC PERSPECTIVES
       1988, pp. 272-274

       Reprinted with permission from World Resources Institute.

THE GREENHOUSE EFFECT AND GLOBAL CLIMATE CHANGE
by James Gustave Speth
President, World Resources Institute

    For the past several years, the international scientific community has been issuing unusual warnings (Mintzer 1987). Earth's climate, the climate that has sustained life throughout history, it says, is now seriously threatened by atmospheric pollution.

    Perhaps the most notable warning came in October 1985, at a conference sponsored by the International Council of Scientific Unions (I.C.S.U.), the World Meteorological Organization (W.M.O.), and the U. N. Environment Programme (U.N.E.P.), in Villach, Austria. "As a result of the increasing concentrations of greenhouse gases," the conference statement began, "it is now believed that in the first half of the next century, a rise of global mean temperature could occur which is greater than any in Man's history" (U.N.E.P. et al. 1985).

    Through such activities as burning fossil fuels, leveling forests, and producing certain synthetic chemicals, people are releasing large quantities of "greenhouse" gases into the atmosphere. These gases absorb Earth's infrared radiation and prevent it from escaping into space. This process traps heat close to the surface and raises global temperatures.

    Excess carbon dioxide (CO2) is the main offender. Prior to the Industrial Revolution, the concentration of CO2 in the atmosphere was about 280 parts per million. At this concentration, CO2 (and water vapor) warmed Earth's surface by about 33 degrees Celsius and made Earth habitable. But, since then, especially since 1900 or so, the accelerating use of fossil fuels and vegetation loss over large areas of the planet have caused CO2 in the atmosphere to increase by about 25 per cent, to 348 parts per million.

    But CO2 buildup is not the only problem. Much of the new urgency about the greenhouse effect stems from the realization that other gases released through human activity--including C.F.C.s, methane, nitrous oxide, and ozone--now contribute about as much to the greenhouse effect as CO2 does.

    According to one estimate, past emissions of greenhouse gases have already committed Earth to an average warming of 1 degree to 2.5 degrees Celsius over that of the pre-industrial era (Ramanathan 1987), though only a fraction of this warming has been felt to date because of the inertia of the oceans. Several models project that if current trends in greenhouse gas buildup continue, human activity will have committed Earth to a warming of 1.5 degrees to 4.5 degrees Celsius by around 2030, the upper end being the more probable.

    To find conditions like those projected for the middle of next century, we must go back millions of years. If the greenhouse effect turns out to be as great as predicted by today's climate models, and if current emission trends continue, our world will soon differ radically from anything in human experience.

    While the regional impacts of a global warming are uncertain and difficult to predict, many of the anticipated changes are both far-reaching and disturbing. Rainfall and soil moisture patterns could shift dramatically, upsetting agricultural activities worldwide. Sea level could rise from 1 to 4 feet, flooding coasts and allowing salt water to intrude into water supplies. Ocean currents could shift, altering the climate of many areas and disrupting fisheries. The ranges of plant and animal species could change regionally, endangering protected areas as well as species whose habitats are now few and confined. Record heat waves and other weather anomalies could harm susceptible people, crops, and forests.

    In this context, it is not surprising that the scientists at Villach took the important step of urging that the greenhouse issue be moved into the policy arena. "Understanding of the greenhouse question is sufficiently developed," they concluded, "that scientists and policymakers should begin an active collaboration to explore the effectiveness of alternative policies and adjustments" (U.N.E.P. et al. 1985).

    With the buildup of greenhouse gases proceeding apace, a planetary experiment is under way. Before the results are fully known, future generations may have been irrevocably committed to an altered world--one that may be better in some respects but that also involves truly unprecedented risks.

    In light of these threats, two kinds of action seem justified: adaptive measures to prepare for apparently inevitable climate changes, and, more important, preventive measures to forestall changes that societies can still influence. Control of "greenhouse"-producing gas releases can both buy time and, ultimately, maintain Earth's climate as closely as possible to that of the past several thousand years.

    Given what is now known, major national and international initiatives--grounded in the best available science and policy analysis--should become a top priority of governments and citizens. A deeper appreciation of the risks of "greenhouse"- producing gas buildup should spread to leaders of government and business and to the general public, investing the greenhouse issue with a sense of urgency absent today. If nations are to be spared a Hobson's choice between energy shortages and climate change, we must become committed to energy efficiency, to solar and other new and renewable energy sources (commercial prospects for new solar technologies, particularly photovoltaic solar cells, appear increasingly promising), and to economic incentives and other measures that discourage the use of high-carbon fuels. Additional steps should also be taken to halt deforestation now under way in the tropics and to regulate C.F.C.s and other greenhouse gases.

    The years immediately ahead should be a period of intense scientific research, policy exploration, and adoption of appropriate measures. Innovative international responses should be discussed. Global and regional energy futures should be explored and we should especially emphasize their effects on the greenhouse problem. Preventive and adaptive strategies appropriate to the world's regions should be mapped and means found to build U.S.-Soviet cooperation on this issue since these two countries together have most of the world's coal reserves. (For discussions on the greenhouse effect and climate change, see: Mathews 1987, Mintzer 1987, U.N.E.P. 1987c.)