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 favour 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 Nino weather pattern to mosquito ecology and human cells’ ability to withstand heat.“We are not dealing with a single toxic agent or a microbe where we can put our finger with certainty on an exposure and the response,” said Jonathan 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—when warming is expected to accelerate, but people may prepare for it—is 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.Most of the increased burden of death and disease was from malnutrition, diarrhoea, malaria, heat waves and floods. But those diseases will play a minor role, at best, in many regions that will feel the effects of global warming. To organise their thinking and focus the attention of policymakers, researchers put the health effects of climate change into five groups.Heat stressThe 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 since the 1500s, when about 30,000 people died of heat-related illness.People who were old, very young, ill, immobile or poor were at highest risk—and are likely to make up a bigger slice of the population in the future. About 20 percent of people in industrialised 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 9 degrees Fahrenheit warmer on average than surrounding rural areas.A study published three years ago examined mortality on hot days in 28 cities in the last third of the 20th century. Death rates were lower in the 1980s and 1990s than in the 1960s and 1970s in most places. This steady decline in heat-stress death was almost certainly the consequence of air conditioning, better awareness of the problem and improved medical care.“If there is a very effective response system, then even in hotter temperatures you may not see more deaths,” said Kristie Ebi, an epidemiologist and consultant in Alexandria. She helped write the health chapter of the most recent report of the United Nations’ Intergovernmental Panel on Climate Change, which was this year’s Nobel Peace Prize winner along with Al Gore.Extreme weatherClimate change is expected to increase the severity of storms, especially ones associated with cyclical events such as the El Nino Southern Oscillation. Flooding is the most common weather disaster, responsible for the deaths of about 100,000 people and the displacement of 1.2 billion from 1992 to 2001. The worsening of this hazard will vary by region. It is expected to change little in Southeast Asia by 2030, but it may increase 50 percent in West Africa and quadruple in Central and South America.Rising oceans also threaten coastal populations. Of the world’s 20 megacities, 13 are at sea level. Greater variability in weather patterns along with higher temperatures may lead to droughts and water shortages. Today, 1.7 billion people live in places that have periodic water shortages. The number is expected to increase to 5 billion by 2025.Air pollutionClimate change affects air pollution in two ways. Heat speeds chemical reactions and consequently may worsen pollution from ozone and airborne particulates, or soot. It may also spur pollen production by plants, which could worsen asthma and allergies in some people. Water- and food-borne diseaseHigher temperatures and torrential rains are likely to cause outbreaks of some diarrhoeal diseases. A recent study of waterborne-disease outbreaks in the US in the past 50 years found that 67 percent were preceded by heavy rainfall. Overall, climate change may increase the burden of diarrhoea, mostly in developing countries, by 2-5 percent by 2020.Vector-borne diseaseScientists suspect that many diseases transmitted by insects and animals will become more common, though there is more uncertainty about this than other consequences of global warming. Dengue and malaria are most likely to increase. In the US, most public debate has been on ways to slow global warming, not dampen or prevent the inevitable effects. “We are a good decade behind Europe in designing and developing adaptations,” said Ebi. Such planning is wise not only for the federal government and states, but for cities and towns too. “The impacts of climate change really do depend on your local context,” she said. -David Brown (LAT-WP)
