Global warming: public health and the debate about science and policy.

Considerable attention continues to focus on the science and policy aspects of the global warming debate and the potential for negative health effects associated with the predicted changes in climate patterns. As with many public policy issues, the debate is shaped by two competing views. There are those who say it is all a hoax and compare global warming to alar in apples, Times Beach, and the cranberry scare of 1959. Others suggest that we are beginning to see the effects of global warming now and should take decisive action to slow the change that is taking place. Where on this continuum does the truth lie? That is the issue for science and policy.

As has been the case with other environmental issues, the science is not definitive. We must extrapolate from what is known to predict what will happen.

A fundamental point is being overlooked, however, while scientists debate and economists worry. That point is a message about prevention, protection of public health, and preservation of the environment, all of which should influence the interim policy decisions made while we wait for greater scientific certainty. There is sufficient science to support steps toward mitigation or prevention of adverse effects even in the absence of a complete explanation of global warming as a short-term anomaly or a prelude to irreversible change.

Paul Epstein, of the Harvard Medical School, has described a framework for assessing health, climate change, and ecosystem vulnerability. Using the analogy of the disease triangle (agent, host, and environment) Epstein's framework defines three spheres: climate system, ecosystems, and social systems. Each of those three spheres can influence the nature and rate of change in the others. The current dispute among scientists and policy makers concerns the specific influence of the climate system sphere, particularly the implications of the global warming phenomenon. There is less uncertainty, however, about the factors that influence change in the other spheres. For example, it is known that the consumption of fossil fuels is generating greenhouse gases and releasing them into the atmosphere at an unprecedented rate. Likewise, activities such as deforestation are changing and, in some cases, destroying ecosystems. It is also known that these changes entail a loss of diversity through the extinction of plant, insect, and animal species. Environmental factors include overharvesting, loss of habitat, and the emission of chemical pollutants. Each of those factors can be measured quantitatively.

While the meaning of the rise in global temperature and effects such as increasing ocean levels continue to be disputed, the spread of certain diseases has been clearly documented. Those diseases have been found at latitudes where they have not previously been identified. The increased incidence of hantavirus, malaria, cholera, and toxic algal blooms suggests a change in ecological balance and predator-prey relationships that can influence the risk of disease in humans. Regardless of whether there is a proven relationship between global warming, climate changes, and the emergence of new patterns of infectious disease, the public health community is obligated to investigate these new trends and determine what additional analysis and intervention are necessary. Public health practitioners frequently respond to disease incidence well before any cause-effect relationship has been established. The determination of causal factors will ultimately enhance the ability to intervene effectively, but the lack of such a determination does not have to be a barrier to response.

Scientists are facing the following questions: What is the capacity of the global environment to manage the assault by greenhouse gases, pollutants and human activity? If we have not yet exceeded that capacity, when will we do so? While that debate takes place though, the practical issue for public health professionals and policy makers is what should be done now to reduce the influence on two spheres of the Epstein framework, the ecological and social systems. What are the emerging risks, where are they, and what can be done to preserve the ecological balance that remains where ecosystems have not been significantly altered?

Meanwhile, the debate about the science of global warming has attracted the attention of economists and industrialists who fear the response to the problem will sacrifice economic development and prosperity, especially in the United States. Does environmental protection add value to the economy, or does it dampen economic activity and prosperity? Economic fears and the consequent debate appear to be acting as a barrier to prudent action, which would address the imbalance that human activity is causing in the three spheres described above. Specifically, such action might use known and affordable technology to reduce greenhouse gas emissions, reduce the emission of chemical pollutants into the atmosphere, and slow the destruction of ecosystems that results from overharvesting the development of land for commercial gain. Furthermore, there should be a sense of some urgency in addressing this issue. It does not take much science to see the impact that continued population growth and the corresponding consumption of finite natural resources will eventually have on the health of the global environment. The issue is how long it will be before key resources are depleted or the balance of nature is altered irreversibly, outrunning our capacity to adapt.

The U.N. Panel on Climate Change has concluded that the energy balance of the atmosphere has been altered as a result of human activity. Furthermore, it is the opinion of the panel that the global environment is entering or has entered a period of climatic instability and warming likely to cause widespread economic, social, and environmental dislocation over the next century. Regardless of the cause of that change, it is important, in the spirit of prevention, to continue to find ways to reduce or at least slow the impact of human activity on the environment.

Disturbing trends are apparent in the climate system and the ecosystems as well as in the influence of social systems on the other two spheres. These trends will ultimately have a profound impact on the health of our global environment and the human population. Many times in the history of environmental protection in the United States, decisive action has been taken and significant resources allocated to eliminate pollutants that represented virtually no global risk and concerning which the science was indecisive at best and sometimes even suspect. Should global protection be afforded the same consideration that the air, land, and water of the United States have received throughout the modern era of environmental protection? There is a middle ground between no action and the doomsday economic forecasts about overreaction to the issue of global climate change. Public health and environmental professionals must rise above the debate to be sensitive and responsive to the changing trends in the influence of the global environment on human health. In fact, public and environmental health professionals should have the loudest voice in promoting prudent steps now that will prevent adverse effects in the future. After all, we place our confidence in prevention rather than in treatment, don't we?