Global climate change: components and consequences.

Since the December 1997 meeting of world leaders in Kyoto, Japan, the issue of global climate change has been the subject of "heated" discussions. In June NEHA's Council of Delegates adopted a position on global climate change (Journal of Environmental Health, November 1997). Given the current arguments and misconceptions surrounding this issue, I thought it would be useful to revisit the topic of global climate change.

Global warming and global climate change have become synonymous in the public's mind. As environmental health professionals, we know the difference is vast. Although temperature change is certainly a major component, many other factors contribute to the problem of climate change.

Climate change has three basic components. First, if the Earth's energy balance is altered, the climate of the Earth is also altered. In 1896, a Swedish scientist, Svante Arrhenius, was the first to note an increase in the amount of atmospheric carbon dioxide (C[O.sub.2]), primarily caused by increased industrial activity. Indeed, C[O.sub.2] has increased by 25 percent in the last 250 years, and C[O.sub.2] is predicted to double by the middle of the next century. Plants, which remove C[O.sub.2] from the atmosphere, have been unable to keep up with demand resulting from the higher C[O.sub.2] levels and increased deforestation. The increased C[O.sub.2] has acted as a blanket, keeping solar energy trapped below it. In addition, release of chlorofluorocarbons from aerosol cans, rockets, and supersonic aircraft has depleted the ozone layer; consequently more solar radiation reaches Earth. The planet no longer is capable of releasing energy at the same rate it absorbs it. The energy budget has become unbalanced.

The second component of climate change is the effect particulates have on the earth's precipitation patterns. Levels of particulate matter, such as smoke and dust, have greatly increased in our atmosphere; this matter is then available to form precipitation nuclei. Two excellent examples of altered precipitation are in the U.S. Midwest, where transpiration from corn crops has been found to fuel storm systems, and in Australia, where smoke particles from burning sugar cane stubble have formed such good precipitation nuclei, that areas downwind of the cane fields have experienced a 20 percent drop in precipitation.

The third component is the effect of heat produced by human activities. The best examples of this effect are thermal blankets created by urbanization. Also, acid rain forms when sulfur and nitrogen oxides, which are released into the atmosphere by the burning of fossil fuels, combine with water. Acid rain contributes to desertification, and, once again, increased temperatures result.

Many other events can contribute to climate change, such as small sustained changes in the water balance as a result of urbanization, erosion, and increased irrigation; radioactive contamination from testing and use of nuclear weapons; and water pollution at levels too high to permit renewal of purity. All of these factors can alter our climate, perhaps in ways we have yet to determine.

What are the potential impacts of climate change? Climatic oscillations, tracked by the Extreme Event Index, have increased exponentially in the past four decades. According to the National Oceanic and Atmospheric Administration, July 1998 had the highest recorded temperatures since weather records have been kept, and, according to the National Climatic Data Center, the 1990s have been the hottest decade in 600 years.

Possible agricultural effects are less well defined. On the one hand, the melting polar ice would cause sea levels to rise, and arable land would be inundated with salt water. In heat-stricken areas, soil moisture would be reduced. Climatic zones would shift, forcing zonal vegetation into different, possibly unfavorable, soils. Changes in temperature could interfere with plant life cycles. On the other hand, increased C[O.sub.2]would make plants grow bigger and become more water efficient. Growing seasons would become longer.

Beyond the obvious examples, such as increased heat and cold injuries, are many other health effects that could have an even more dramatic impact. Increased numbers of skin cancers and cataracts have already been attributed to ozone depletion. Many infectious diseases once confined to specific climatic regions are now spreading to areas where climate changes have made their presence possible. Perhaps even more devastating would be the secondary effects, such as disruption of sanitation and health services during extreme events, malnutrition, and dehydration resulting from lack of clean water supplies. The social effects of climate change (economic, cultural, and political) could cause migration of "eco-refugees" into already stressed communities.

All is not doom and gloom, however. As environmental health experts, we can support the development of technologies that not only conserve energy and materials but also reduce greenhouse emissions. We can support reforestation technologies and use appropriate energy planning to reduce reliance on fossil fuels. We can promote the development of and infrastructure for water purification and storage. We can encourage a continued corporate transition to sustainable environmental programs.

We are fortunate to have a national leader such as Vice President Al Gore who recognizes the threats to our environment and is prepared to suffer political attacks for his support of technologies aimed at reducing climate change. If we are to "think globally and act locally," we must understand that this also means support of controversial conservation programs. I support the Vice President's efforts - and have written to let him know of my support.

How about you?