Science Forum
The major problem confronting researchers studying the greenhouse effect and global warming is that there are so many variables involved it is almost impossible to tie any atmospheric changes to the theory.
Thus it seemed the height of hubris last year when James Hansen of NASA’s Goddard Institute for Space Studies bet that one of the first three years of the 1990s would be the hottest on record. As it turned out, it was a safe bet; a recent article in the journal Science, published by the American Association for the Advancement of Science, reported that, by three independent measures of global temperature, 1990 was the hottest year on record. The question now is whether Hansen is on to something and the greenhouse effect is real and immediate, or did he luck out.
“I think he lucked out,” says Hugh Ellsaesser of the Lawrence Livermore National Laboratory, who is still of the opinion that it is far too early to say that greenhouse warming has arrived. Ellsaesser was the only researcher to call Hansen’s bet, an act that cost him $100.
Although he was the loser, most climatologists agree with Ellsaesser that there is nowhere near enough evidence to predict that greenhouse warming has begun, let alone attribute a single, abnormally warm year to its effect. What happened in 1990 has nothing to do with the greenhouse effect, says climatologist Chester Ropelewski of the National Oceanic and Atmospheric Administration. However, the fact that climatologists discount the recent hot spell does not mean they do not believe greenhouse warming will not occur.
Science reported on a poll of 1,500 environmental scientists from 41 countries conducted by the Global Environmental Change Report of Massachusetts. Almost 90 percent favored taking immediate steps to reduce atmospheric carbon dioxide and other greenhouse gases. At the same time, only 65 percent believed there was better than an even chance that any significant warming would take place over the next century.
In 1989 the U.S. Department of Energy issued a report that certainly suggests the planet has been warming over the past several years. Before 1990, the year 1987 was the warmest on record and the decade of the 1980s had four of the warmest years on record. The report goes on to say that the average surface air temperature has increased by nearly 1 degree (0.5 degree Celsius) since 1850 and the start of the Industrial Revolution.
Hansen found the world is heating up even faster than the government report indicates. He found that the planet was 0.45 degree Celsius warmer than normal in 1990. Normal in this case is the average global temperature from 1951 to 1980 and does not include any of the “hot” years from the 1980s. This is a huge increase considering it equals that generally accepted for the past 150 years.
Climatologists trying to convince their governments that the greenhouse effect is real find themselves with a frustrating dilemma. At present there is not enough hard evidence to predict when the warming will take place or how severe it will be. If, on the other hand, the world waits to collect the necessary data, it will be too late to respond to its consequences. In the meantime, scientists have to content themselves with global climate models that they hope mirror the environmental changes taking place. These models, often called General Circulation Models (GCMs), are extremely complex and involve a great number of variables.
The basic premise is fairly simple. Certain gases in the atmosphere, primarily carbon dioxide, methane, water vapor, and nitrogen oxide gases, are transparent to some types of radiation while opaque to others. These gases allow ultraviolet radiation from the sun to reach the Earth’s surface during daylight hours but slow cooling at night by preventing infrared radiation from escaping back into space. This causes a gradual buildup of heat energy at the planet’s surface.
One frequently cited prediction from the National Academy of Sciences is that a doubling of atmospheric carbon dioxide will cause the average global temperature to increase by 1.5 to 4.5 degrees Celsius. If there was a direct, linear relationship between the amount of greenhouse gas in the atmosphere and temperature increase, the estimate would not vary so greatly. Unfortunately, there are many other factors to be taken into consideration.
Snow and ice play a significant role in that their surfaces are reflective and, by reflecting instead of absorbing solar energy, tend to keep warming from occurring. As temperatures rise, snow and ice will melt thereby cutting down on reflectivity and accelerating the warming trend. Moreover, the melting will cause an increase in atmospheric water vapor trapping more energy and hurrying the process. But this is not the entire story because an increase in atmospheric water vapor will cause thicker cloud covers that prevent solar radiation from getting to the Earth’s surface. Which of these effects are the most important? No one knows.
Another important, and largely unknown factor, is the role of the atmosphere and oceans as a sort of global thermostat. Some of the solar energy deposited on the ocean’s surface will be carried deep by currents. Much of it, however, is involved in the evaporation and precipitation cycle that tends to keep the surface temperature constant.
Many climatologists suspect this hydrologic balance has been altered but again this is not proven. Even the ocean’s plankton are getting into the act. Some researchers speculate that, as carbon dioxide rises in the atmosphere and the top few meters of the ocean warms, populations of one-celled animals will explode. Many of these form carbonate shells, an action that removes carbon dioxide from the atmosphere. There are hundreds of similar factors researchers know very little about but have to be factored into global climate models.
Given the uncertainties, Hansen’s winning of his rash bet was probably luck. The Science article does say that one aspect of the 1990 heat wave has intriqued the climatologists. The hot weather was not accompanied by an El Nino, a surge of warm water that periodically appears in the South Pacific and helps to raise global temperatures. A large El Nino in 1986, for example, was followed by record temperatures in 1987. None was observed in 1989 yet 1990 was the hottest year on record. Again, there is no easy explanation. An El Nino is expected this year so it will be interesting to see what 1992 brings.
Any hope of controlling a future greenhouse effect lies with the high-energy use countries such as the United States, the Soviet Union, and the European Economic Community. An article in Environmental Science Technology spoke somewhat pessimistically about any global consensus happening. Given the uncertain nature of greenhouse warming research, it is unlikely any government will put itself at an economic disadvantage to curb it. The U.S. government is on record as advocating further study. The unfortunate fact is that, when all the facts are in, it will be too late to do anything about it.
Clair Wood, a science instructor at Eastern Maine Technical College, is the NEWS science columnist.
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