As Temperatures Rise, Health Could Decline
Monday, December 17, 2007
Depending on where you are, this is going to be a hotter, wetter, drier, windier, calmer, dirtier, buggier or hungrier century than mankind has seen in a while. In some places, it may be deadlier, too.
The effects of climate change are diverse and sometimes contradictory. In general, they favor instability and extreme events. On balance, they will tend to harm health rather than promote it.
That is the majority view of scientists trying to solve an equation whose variables range from greenhouse gas concentrations and the El Niño weather pattern to mosquito ecology and human cells' ability to withstand heat.
"We are not dealing with a single toxic agent or a single microbe where we can put our finger with certainty on an exposure and the response," said Jonathan A. Patz, a physician and epidemiologist at the University of Wisconsin at Madison. "Climate change affects everything."
Predictions of how global warming could affect people's health are crude. They are based on the experience of the past several decades, when there has been a small, well-documented rise in the temperatures of the planet's atmosphere and oceans. What that says about the future -- a time when warming is expected to accelerate, but people may be able to prepare for it -- is quite uncertain.
In the last quarter of the 20th century, the average atmospheric temperature rose by about 1 degree Fahrenheit. By 2000, that increase was responsible for the annual loss of about 160,000 lives and the loss of 5.5 million years of healthy life, according to estimates by the World Health Organization. The toll is expected to double to about 300,000 lives and 11 million years of healthy life by 2020.
The biggest tolls were in Africa, on the Indian subcontinent and in Southeast Asia. Most of that increased burden of death and disease was from malnutrition, diarrhea, malaria, heat waves and floods. But those diseases will play a minor role, at best, in many regions that nevertheless will feel the effects of global warming.
To organize their thinking -- and to focus the attention of policymakers -- researchers tend to put the health effects of climate change into five groups.
The most obvious effect of global warming is hotter weather.
Scientists predict that heat waves will be longer and more frequent in the future. Their worst-case effects may have been glimpsed in Europe's summer of 2003, the hottest spell there since the 1500s. About 30,000 people died of heat-related illness, including 14,800 in France in three weeks in August.
People who were old, very young, ill, immobile or poor were at highest risk. Although the human body can adapt somewhat to chronically higher temperatures, those groups will remain vulnerable -- and they are likely to make up a bigger slice of the population in the future.
About 20 percent of people in industrialized countries are over age 60 today. That figure will rise to 32 percent by 2050. More people will also live in cities -- 61 percent of the world's population by 2030, compared with 45 percent now. Cities are "heat islands," 9 degrees Fahrenheit warmer on average than surrounding rural areas and resistant to the cooling effects of night.