Canada — Smoke from burning forests and grasslands kills on average 339,000 people a year world-wide, an international research team said Sunday in the first systematic global health study of air pollution from wildfires.
Every year, accidental and deliberate wildfires burn an area that, taken together, is larger than India. The dense plumes of fine particles and compounds released in the complex chemistry of combustion typically stay aloft for weeks and can travel hundreds of miles downwind. Smoke from fires in Central Siberia during 2003, for example, caused air pollution in the U.S.
To estimate the public health consequences, scientists led by fire researcher Fay Johnston from the University of Tasmania in Hobart, Australia, studied the impact of the fine particulate matter released during such blazes between 1997 and 2006, using satellite data, computer models of wind patterns and mortality tables developed by the World Health Organization.
“I personally was surprised that the estimate of deaths was so high,” said Dr. Johnston, who presented the findings at a symposium Sunday during a meeting of the American Association for the Advancement for Science in Vancouver. The findings were also published online in the journal Environmental Health Perspectives.
Southeast Asia and sub-Saharan Africa were hit hardest by the ill effects of smoke from wildfires and deliberate burning for clearing land, the research team said.
In Africa, about 157,000 people died annually as a consequence of smoke pollution, the scientists said. In Southeast Asia, 110,000 on average were killed every year by medical conditions related to inhalation of wildfire smoke.
By comparison, public health experts estimate that urban air pollution generally kills about 800,000 people every year, and the indoor fumes from household fuels cause about 1.6 million deaths annually.
The medical consequences of smoke from wildfires are likely to worsen in coming years, however, if predictions of long-term rising temperatures due to heat-trapping greenhouse gas emissions come true, researchers at the AAAS meeting said.
Hotter and drier summers to come will result in longer fire seasons and more intense wildfire fires that may be harder to control, they said.
“A warmer world is going to see more fire,” said senior researcher Mike Flannigan at the University of Alberta and Natural Resources Canada. By his computer climate projections, which he completed last week, wildfire activity world-wide could double or triple within 50 years or so. The wildfires could also become more intense and perhaps unmanageable. Other researchers have reported similar conclusions in recent years.
“The warmer it is, the longer the fire season; the warmer it is, the more lightning we have; the warmer it is, the drier our fuels are,” he said.
Researchers have estimated that for each additional degree centigrade in global mean temperature, there could be more storms and a 5% increase in the amount of lightning, which can ignite dry forests and savannahs.
“The risk to life and infrastructure is only going to increase,” Mr. Flannigan said.