signed, local institutions must often relyon the integrity of the foreign partner insharing information. “You have no wayof knowing” what happened to a sam-ple, notes Berhanu M. Abegaz of theUniversity of Botswana. On occasion, adrug developer may offer to cultivate a

plant in the source country, Abegaz says.Nevertheless, he adds, this arrangementcan have a double edge: the firm thatholds the patent can also control theprice paid to farmers, and the produc-ers are kept at a subsistence level.

The more land brought under cultiva-

tion, the greater may be the threat tobiodiversity. And if collected from thewild, the plant itself may become endan-gered. That happened with the Pacificyew, which yields the anticancer agenttaxol. If a drug can be synthesized in thelaboratory, the pressure on biodiversity

News and Analysis24 Scientific American May 1996

Certain gases in the atmosphere allow visible light topass through, but they block much of the heat reflect-

ed from Earth’s surface—in the same fashion as the glasswindows in a greenhouse. Without this greenhouse effect,worldwide temperatures would be lower by 35 degrees Cel-sius, most of the oceans would freeze, and life would ceaseor be totally altered. According to the theory of global warm-ing, an increase in greenhouse gases in the atmosphere willproduce unacceptable temperature increases. A doubling ofthe volume of gases, for example, would cause temperaturesto go up by 1.5 degrees C or more, a phenomenal changeby historical standards.

The most dramatic consequence of the warming wouldbe a rise in sea level from the melting of polar ice caps, arise that the Environmental Protection Agency projects tobe 20 feet as early as the year 2300—sufficient to submergelarge parts of coastal cities. Global warming would result inprofound shifts in agriculture and may, as some have sug-gested, hasten the spread of infectious diseases.

Aside from water vapor, the principal greenhouse gasesare carbon dioxide, resulting from the burning of fossil fuels;methane, produced by the breakdown of plant materials bybacteria; nitrous oxide, produced during the burning of fossilfuels and by the decomposition of chemical fertilizers andby bacterial action; and chlorofluorocarbons, used for indus-trial and commercial purposes, such as air conditioning. Ofthese, carbon dioxide is the most important. The atmospher-ic concentration of CO2 was 280 parts per million before

the Industrial Revolution; with the increasing use of fossilfuels, it has risen to more than 350 parts per million today.

The idea of global warming gained support as tempera-tures soared to record levels in the 1980s and 1990s, butthere are several problems with the theory, including doubtsabout the reliability of the temperature record. Despite thisand other questions, a majority of climatologists feel that arisk of global warming exists, although there is much dis-agreement concerning the extent and timing. (One of theuncertainties is the possibility that large amounts of meth-ane now locked in Arctic tundra and permafrost could berapidly released if warming reaches a critical point.) At the1992 United Nations Conference on Environment and De-velopment, more than 150 countries signed the U.N. Frame-work Convention on Climate Change, which pledges signa-tories to control emissions of greenhouse gases.

In 1992 the Persian Gulf states of Qatar and the UnitedArab Emirates had the highest per capita emissions of car-bon dioxide—16.9 and 11.5 metric tons, respectively—whereas the U.S. was in eighth highest place with 5.2 metrictons. Overall, the U.S. produced 23 percent of global emis-sions, western Europe 14 percent, the former communistcountries of eastern Europe 20 percent, and Japan 5 percent.Of the developing countries, China was the biggest contrib-utor in 1992 with 12 percent, followed by India with almost4 percent. Although emissions have more than tripled dur-ing the past 40 years, they showed signs of leveling off inthe late 1980s and early 1990s. —Rodger Doyle

METRIC TONS PER CAPITA IN 1992

LESS THAN 1 1 TO 1.99 2 TO 2.99 3 OR MORE

SOURCE: Carbon Dioxide Information and Analysis Center

HONG KONG

SINGAPORE

B Y T H E N U M B E R S

RO

DG

ER D

OYLE

Carbon Dioxide Emissions

Copyright 1996 Scientific American, Inc.