They suspect 150,000 people per year, for the past 30 years, have died as a result of a gradually warming planet. They say that annually, 5 million cases of illness can be attributed to it, too.

And they think things are only going to get worse.

But they say governments can play a role in stemming these escalating temperatures. And the countries most responsible for the warming trend, such as the United States -- which contributes the largest share of greenhouse gases per capita -- should play a role in prevention.

The paper appears in Wednesday's early online edition of the journal Nature.

Infectious Diseases

Looking across the globe, Jonathan Patz, a professor at UW's Nelson Institute for Environmental Studies, and a team of climate and health scientists combed through the scientific literature looking for specific incidences of human-induced climate change and the ill effects it has on people.

They found many.

They cited both broad-scale examples -- such as the 2003 European heat wave that killed nearly 45,000 in two weeks -- and smaller-scale examples, such as the local effects of "urban heat islands," a phenomenon in which cities register temperatures five to 10 degrees warmer than the outlying area.

In both cases, the warmer temperatures have been attributed to human activities, such as the burning of fossil fuels or the design of urban landscapes.

"Climate scientists think that human-induced climate change has amplified the severity of recent extreme events such as Hurricane Katrina and the 2003 European heat wave," which has led to a loss in life, said Tony McMichael, director of the Australian National University's Center for Epidemiology and Population Health, who was not involved in the study.

But there is also "growing evidence that various infectious diseases are changing their geographic range, seasonality and incidence rate in association with ongoing climatic changes," he said.

Global Ethical Challenge

Indeed, mosquitoes, ticks and sandflies -- common vectors of disease -- all react to climate. For example, Patz's team found research that showed an increase in cases of malaria in the highlands of Kenya during periods of extreme heat variability. Another study they noted documented a correlation between warming trends in Ethiopia and malarial infections.

Patz said researchers who have observed West Nile virus' spread across the United States have documented a correlation of its movement with hotter and drier weather -- the peculiar weather of choice for the primary carrier of the virus, the Culex mosquito.

"Climate change is not just another minor environmental problem and incidental health hazard," said McMichael. "A change in Earth's climatic conditions will disrupt many of the natural systems that affect human health," including regional food production, infectious disease agents, patterns of heat stress and exposure to extreme weather events, such as cyclones, floods and fires.

Unfortunately, regions that will bear the biggest brunt of these changes, such as Africa, not only produce some of the lowest per capita emissions of greenhouse gases, said Patz, but have the least ability to adapt and deal with climate change.

"Herein lies an enormous global ethical challenge," he said.

"This is complex and difficult stuff to study," said Howard Frumkin, director of the National Center for Environmental Health at the Centers for Disease Control and Prevention. But he said the paper was important because it covers the "broad range of potential health impacts" caused by climate change.

Rise in Dangerous Ozone Days

According to climate scientists, the Earth's temperature is likely to increase between 2.5 and 10.4 degrees Fahrenheit by the end of the century. As a result, the seas will rise and the number of people at risk from flooding by coastal storm surges is projected to increase.

One of the midrange scenarios that Patz and his colleagues investigated predicts a 15.75-inch rise in sea level by 2080. That rise would increase the number of people at risk from storms and surges from a current level of 75 million to 200 million.

Patz thinks that it'll be communities and regions along the Pacific and Indian coastlines, as well as sub-Saharan Africa, that will be most affected.

But places such as the US Midwest and Northeast will not be impervious to climate changes, said Patrick Kinney, associate professor of environmental health sciences at Columbia University. He cited a rise in dangerous ozone days, which he predicts will continue to increase in number.

McMichael said while some regions may actually benefit from the rise in global temperatures, the effects will be short-lived.

"Yes, in the short term, some temperature-zone regions will gain from improved crop yields, some will benefit from conditions becoming too hot or dry for mosquitoes, and some will benefit from alleviation of extreme cold in winter," he said. But, "in the longer term, if current trends continue, these gains will disappear as conditions become more extreme."

On Nov. 28, global leaders will convene in Montreal at the first meeting of the Conference of Parties to the Kyoto Protocol, which came into effect in February. The United States has not signed the treaty. But Patz is hoping his work will demonstrate the moral obligation of countries with higher per capita emissions to adopt a leadership role in reducing the health threats of global warming.

"The political reserve of policy-makers will play a big role in harnessing the manmade forces of climate change," Patz said.