Inside a greenhouse, it is the glass roof that creates the warmth. The glass lets sunlight stream in. When the sunlight strikes a surface and turns into heat energy, the heat then radiates back toward the sky. The radiated heat strikes the glass, which has the peculiar property of allowing light to pass through much better than it lets heat pass through. Therefore, some of the heat is reflected back down into the greenhouse, and the greenhouse warms up.

For at least 100 years, physicists and chemists have known that carbon dioxide (CO2) in the atmosphere acts like glass covering the earth. [1]CO2 lets sunlight in, but does not let heat out nearly so well. Since 1850, the carbon dioxide content of the atmosphere has increased 30% because of humans burning coal and oil. There is nearly universal agreement among scientists that this will warm the earth. [2] It's only a question of when.

Now evidence is accumulating steadily, indicating that the warming has begun:

** AIR IS WARMING: Global average air temperature over the last century has risen about 0.8 degrees Fahrenheit (F.), which is 0.45 degrees Celsius (C.), according to the Intergovernmental Panel on Climate Change (IPCC). The IPCC is made up of about 200 of the world's leading scientists who specialize in climate studies. In some areas, such as Australia and New Zealand, the increase in air temperature has exceeded the average; in New Zealand, average air temperature has risen between 0.7 and 1.4 degrees F. (or between 0.4 and 0.8 degrees C.). [3]

** OCEANS ARE WARMING: In November, 1994, researchers announced finding a 0.9 degree F. (0.5 degree C.) rise in the temperature of the deep waters of the Indian Ocean, compared to measurements taken 20 years ago. This was the third ocean observed to be warming. In 1992 Nathan Bindoff reported that the subsurface temperature of the southwestern Pacific Ocean had increased at about the same rate (0.9 degrees F. [0.5 degrees C.] over 20 years). [4] In early 1994, a group led by Gregorio Parrilla of the Spanish Oceanographic Institute reported that the North Atlantic was also warming. [5]

** In December, 1994, Ed Carmack of the Institute of Ocean Sciences in Sidney, British Columbia, Canada, reported that the waters 200 to 1000 meters (660 to 3280 feet) beneath the Arctic Ocean have warmed 1.8 degrees F. (1.0 degrees C.) "compared to a few years ago." "There is clear evidence that the arctic is warming," Carmack reported. [6] The Arctic is thus the fourth ocean found to be measurably warming. In June, 1995, researchers used a new technique to measure temperature beneath the Arctic ice cap. They measured the speed of sound through Arctic waters, and from that calculated a warming of 0.9 degrees F. (0.5 degrees C.) compared to thermometer data from a decade ago. [7]

** GLACIERS ARE MELTING. For example, on Mount Jaya in New Guinea, three glaciers have shrunk by 6.2 square miles (16 square kilometers) since 1936, and now only 1.1 square miles (3 square kilometers) of ice remain. "The region has heavy snow showers," says Geoff Hope of the Australian National University in Canberra, "so the shrinking must be due to a rise in temperature." [8]

** PLANT AND ANIMAL SPECIES HAVE BEGUN TO SHIFT THEIR TERRITORY IN RESPONSE TO RISING TEMPERATURES. For example, 45 species of invertebrates were surveyed along the California coastline in 1930 and again in 1993-94. A definite shift northward in the range of these species was observed over the 60-year period. During the period, annual average (mean) ocean temperature at the shoreline increased 1.35 degrees F. (0.75 degrees C.), and average summer maximum air temperatures increased 3.9 degrees F. (2.2 degrees C.). [9]

** In 1994, researchers reported a study of plants on 26 mountain tops in the Alps in western Austria and eastern Switzerland. From "12 very precise historical records" the researchers were able to show that 9 species of plants have been moving upward at the rate of 4 meters (12 feet) per decade since the original measurements were made 70 to 90 years ago. [10] These species are in danger of becoming extinct as they move upward because eventually they will run out of mountain.

** MOSQUITOES ARE SPREADING: Plants are not the only creatures moving northward and to higher elevations. Mosquitoes that carry diseases such as malaria, yellow fever, dengue fever, and encephalitis are also extending their range, and moving to higher elevations --thus threatening larger human populations with exposure to serious infectious diseases. Dengue fever --also known as "breakbone fever" because it is so painful --appeared in Texas this past summer.

In May, 1995, researchers in the Netherlands and in England estimated the increase in malaria that could occur if the IPCC's projection for global warming proves correct. They concluded that, in tropical regions, the "epidemic potential of the mosquito population" would double; on the other hand, in temperate climates, the epidemic potential would increase 100-fold (in other words, it would become 100 times as great as it is today). Furthermore, they said, "There is a real risk of reintroducing malaria into nonmalarial areas, including parts of Australia, the United States, and southern Europe." All told, they estimated that climate change of 5.4 degrees F. (3 degrees C.) in the next century could cause an additional 50 million to 80 million new cases of malaria each year around the globe. [11] Today, about 110 million new cases of malaria occur each year, globally.

The increase of malaria is not merely theoretical. A recent study of a 1987 malaria outbreak in Rwanda showed that 80% of the outbreak could be explained by unusually high temperatures, and abundant rainfall (both of which are expected to increase with global warming). [12] A 1.8 degree F. (1.0 degree C.) temperature increase led to a 337% increase in malaria. Furthermore, there is evidence of a 5-to-8-year cycle of malaria outbreaks in various parts of the world, and these can be shown to correlate with the El Nino Southern Oscillation (ENSO), a periodic warming of the southern Pacific ocean surface, which usually occurs about twice each decade. ENSO ordinarily appears at Christmastime and affects patterns of temperature, rainfall, and drought worldwide for about a year. [13] Since 1980, ENSO events have occurred more frequently, and have lasted longer than they used to. As a writer in SCIENCE magazine said recently, "Recent data suggest that warming in the deep oceans may be driving El Nino conditions...." [14]During the period 1991-1994, El Nino recurred each year --an event without precedent in the historical record. [15] Paul Epstein of the Harvard School of Public Health explains the importance of recent El Nino events this way: Warmer seas evaporate quickly, yielding greater precipitation over some areas and drought in others. The strength of the 1992/1993 El Nino was unexpected, and the endurance of +2 to 3 degree C. (3.6 to 5.4 degree F.) increases in ocean temperatures into summer was unprecedented. As a result of the extended El Nino event of the last 4 years, weather patterns have become particularly erratic and volatile (i.e., unstable), Epstein writes.

** ALGAE ARE BLOOMING. Partly as a result of El Nino events, marine ecosystems around the globe have begun to experience enormous unnatural blooms of algae. Algae are tiny floating plants that photosynthesize, which is to say they use energy from sunlight to combine carbon dioxide and hydrogen (from water) into carbohydrates. Thus algae form the bottom of the oceans' food chains. According to researchers from Harvard University and from the University of Maryland, recent algae blooms threaten the health of marine ecosystems,[16,17] and of humans.

Algae blooms are promoted by many human activities:

** Algae growth is promoted by nitrogen-rich waste waters, by fertilizers, by acid rain, and by nutrient-carrying soil that runs off the land when it rains.

** Wetlands and mangroves ("nature's kidneys") filter out nitrates and phosphates (chemicals which act as fertilizers and promote algae blooms).

** While nutrient sources are increasing, the filtration systems are being lost to coastal development, to aquaculture (fish farming), to diking (a response to rising sea levels, caused by global warming), and to drilling.

** Simultaneously, fish stocks (which eat the creatures that eat algae) are being depleted (14 of 17 major world fisheries are in serious decline).

** Simultaneously, climate-related warmer sea-surface temperatures also increase growth of algae by: (1) increasing photosynthesis and speeding up the algae's metabolism; (2) increasing nutrient-rich coastal upwelling (upward flows of water); and (3) shifting the community of organisms toward more toxic species ("red tides," fish and shellfish poisonings) which are in turn less palatable to creatures that eat algae.

Why should humans care? For one thing, algae provide a home for the microbe that causes cholera --an illness that kills humans by a violent diarrhea, if not promptly and expertly treated. In 1991, El Nino and algae blooms contributed to a massive outbreak of cholera in Latin America in which 500,000 people fell ill and 5000 died. [16]

In sum, "The spread if infectious diseases will be the most important public health problem related to climate change," says Jonathan Patz, a microbiologist at Johns Hopkins University. [14]
                                                                         --Peter Montague
===============
[1] Svante Arrhenius, "On the Influence of Carbonic Acid in the Air Upon the Temperature of the Ground," PHILOSOPHICAL MAGAZINE (1896) cited in Douglas Cogan, THE GREENHOUSE GAMBIT (Washington, D.C.: Investor Responsibility Research Center, 1992), pg. 63.

[2] Kathy Maskell, Irving M. Mintzer, and Bruce A. Callendar, "Basic science of climate change," THE LANCET Vol. 342, No. 8878 (October 23, 1993), pgs. 1027-1031.

[3] Tim Thwaites, "Are the Antipodes in hot water?" NEW SCIENTIST November 12, 1994, pg. 21.

[4] Nathan L. Bindoff and others, "Warming of the water column in the southwest Pacific Ocean," NATURE Vol. 357 No. 6373 (May 7, 1992), pg. 59.

[5] Gregorio Parrilla and others, "Rising temperatures in the subtropical North Atlantic Ocean over the past 35 years," NATURE Vol. 369 No. 6475 (May 5, 1994), pgs. 48-51.

[6] John Travis, "Taking a Bottom-to-Sky 'Slice' of the Arctic Ocean," SCIENCE Vol. 266 (December 23, 1994), pgs. 1947-1948.

[7] Antonio Regalado, "Listen Up! The World's Oceans May Be Starting to Warm," SCIENCE Vol. 268 (June 9, 1995), pgs. 1436-1437.

[8] Helen Goss, "Meltdown warning as tropical glaciers trickle away," NEW SCIENTIST June 24, 1995, page unknown.

[9] J.P. Barry and others, "Climate-Related, Long-Term Faunal Changes in a California Rocky Intertidal Community," SCIENCE Vol. 267 (February 3, 1995), pgs. 672-675.

[10] Georg Grabherr and others, "Climate effects on mountain plants," NATURE Vol. 369 (June 9, 1994), page unknown. See also Carol Kaesuk Yoon, "Warming Moves Plants Up Peaks, Threatening Extinction," NEW YORK TIMES June 21, 1994, pg. C4.

[11] Willem J.M. Martens and others, "Potential Impact of Global Climate Change on Malaria Risk," ENVIRONMENTAL HEALTH PERSPECTIVES Vol. 103, No. 5 (May 1995), pgs. 458-464.

[12] Michael E. Loevinsohn, "Climatic warming and increased malaria incidence in Rwanda," THE LANCET Vol. 343 (March 19, 1994), pgs. 714-718.

[13] M.J. Bouma and others, "Climate change and periodic epidemic malaria," THE LANCET Vol. 343 (June 4, 1994), page unknown.

[14] Richard Stone, "If the Mercury Soars, So May Health Hazards," SCIENCE Vol. 267 (February 17, 1995), pgs. 957-958.

[15] Paul R. Epstein, "Emerging Diseases and Ecosystem Instability: New Threats to Public Health," AMERICAN JOURNAL OF PUBLIC HEALTH Vol. 85, No. 2 (February 1995), pgs. 168-172.

[16] Paul R. Epstein and others, "Marine Ecosystems," THE LANCET Vol. 342 (November 3, 1993), pgs. 1216-1219.

[17] Elizabeth Culotta, "Red Menace in the World's Oceans," SCIENCE Vol. 257 (September 11, 1992), pgs. 1476-1477.

Descriptor terms: greenhouse effect; greenhouse gases; carbon dioxide; air pollution; atmosphere; coal; oil; fossil fuels; combustion; air temperature; global warming; oceans; glaciers; mosquitoes; dengue fever; yellow fever; malaria; encephalitis; rwanda; el nino southern oscillation; enso; paul epstein; algae; eutrophication; fertilizer; nutrients; mangroves; wetlands; aquaculture; fish; cholera; infectious diseases;