WASHINGTON — In the fierce heat and drought of the summer of 1988, talk about global warming took on new significance. The fact that the 1980s have seen four of the hottest years on record appears to more and more scientists as not just another weather cycle, but an outgrowth of the "greenhouse effect."
By describing global warming as a huge hobgoblin needing herculean international efforts, scientists and environmentalists may have missed an opportunity to show individuals how they can help manage the most critical environmental and economic issue of their lifetimes.
Positive action to offset global climate change is doable by anyone with hands strong enough to get a tree seedling in the ground. If we consider the whole picture of the causes and possible solutions to global warming, such a simple act as planting trees could have significant effects.
About half the greenhouse effect is caused by an increase in atmospheric carbon dioxide. Human activities have raised the amount of carbon dioxide in the atmosphere in recent decades, largely in two ways:
First, we have burned huge supplies of fossil fuels, thereby accelerating the transfer of carbon from terrestrial forms to atmospheric gas. Second, we have significantly deforested the Earth. Slashing and burning forests has contributed to a major carbon transfer from earth to air. And that same loss of forest has reduced the amount of plant life available to undertake the critical opposite transformation: taking carbon dioxide out of the air and returning it to terrestrial forms.
Plants, through the process of photosynthesis, take up carbon dioxide, use it as a basic building block for new organic compounds and give off gaseous oxygen in the process. The former carbon dioxide is then stored--as cellulose in a tree trunk, muscle tissue in an animal that eats leaves, or in the body of a soil bacterium. It will remain there until released to the air again through respiration, burning or chemical transformation. This is the carbon cycle basic to all life on Earth.
Humans have exacerbated the greenhouse effect by affecting both sides of the carbon equation--accelerating the release of carbon dioxide to the air and cutting back on the return cycle by demolishing forests.
We need to reduce those activities that cause carbon gassification; we need to speed up the return processes. Happily, people can do both, starting right at home.
The vision of a peaceful human settlement in a hot climate is one of a tree-shaded oasis. In fact, today's urban areas, with temperatures 3 to 10 degrees warmer than the surrounding countryside, resemble deserts in need of oases. So-called "heat islands" are a product of multiple factors: heat produced by autos, buildings, factories; extra heat absorbed by sun-bathed blacktop streets and parking lots; heat absorbed by dark buildings.
Transforming urban heat islands into oases is possible, and we know how to do it. It will require changes in building design and colors and, least expensive to accomplish, it will require more and healthier trees.
Laboratory models show that having three shade trees on the south and west sides of a house can lower air conditioning bills by up to half, depending on conditions in the community. The total effect, in terms of reduced power demands and energy consumption, could translate into significant impact on national carbon dioxide reduction goals.
Right now, the American Forestry Assn. estimates that there are 100 million spaces where additional trees could be planted around American homes and communities.
Urban tree-planting is not the only effort needed. Reduction of fossil fuel emissions is also a step in the right direction. The United States, responsible for almost one-fourth of the world's energy consumption, has many conservation techniques that can significantly affect the total imbalance in the transfer of carbon dioxide from earth to air. But planting urban trees is one of the most cost-effective. It is available immediately. It can be done by ordinary citizens and local organizations, proceeding without massive new investments or new technology.
Tree-planting in rural areas, on lands so subject to soil erosion that they shouldn't be cropped anyway, could add substantially to the reduction of carbon dioxide. So could thinning the trees in existing woodlands so that remaining trees grow more rapidly. Scientists estimate that improving the woodlands could remove as much as one-third of the total carbon dioxide now being released into the air by the burning of fossil fuels.