It's a vicious cycle: Global warming is increasing the chances of wildfires, and now we know the reverse is also true. Scientists have confirmed that wildfires release large amounts of heat-trapping carbon dioxide into the atmosphere. That's no surprise, but the amounts are jaw-dropping: Big fires like the recent ones in California can belch out as much carbon dioxide in a few weeks as all of the state's motor vehicle traffic does in a year.

Christine Wiedinmyer of the National Center for Atmospheric Research and Jason Neff of the
University of Colorado used satellite observations of fires and a new
computer model to estimate carbon dioxide emissions based on the amount of vegetation burned. The California fires broke out after their paper, published online yesterday in
the journal Carbon Balance and Management, was already written. However, a preliminary calculation by Wiedinmyer suggests that the fires emitted
7.9 million metric tons of carbon dioxide in just the one-week period
of October 19-26. That's about 25 percent of the average
monthly emissions from all fossil fuel burning throughout California.—Dawn StoverImage: Jeff Turner, Wildfire in Santa Clarita

The mercury is rising in more ways than one. As our planet warms, wildfires such as the recent blazes in California are expected to become more common. And, a recent study shows, such fires are a major source of mercury emissions.

The map at left shows the annual average (in metric tons) of mercury, a toxic metal, released into the atmosphere by fires. The estimates are based on fires from 2002 to 2006.

Scientists at the National Center for Atmospheric Research in Boulder, Colorado, calculate that fires in the continental U.S. and Alaska release about 44 tons of mercury every year. Industrial sources such as power plants and incinerators release about 108 tons.

Leaves and ground litter absorb mercury from the atmosphere. When a fire breaks out, the stored mercury is released back into the atmosphere. It is particularly dangerous if it ends up in rivers and lakes, where it can be taken up by fish. Pregnant women and children are discouraged from eating some types of fish because of high mercury levels, which can cause neurological and development problems such as attention and language deficits.—Dawn Stover

Image: National Center for Atmospheric Research

At this time next year, the world's finest athletes will converge in Beijing for the 2008 Olympics. They will sprint, leap, and toss their way to gold-that is, if they can get a breath of clean air. China has some of the worst pollution in the world, and bad air kills 400,000 Chinese annually [see "China's Green Evolution." In anticipation of the Olympics, Beijing has launched a massive cleanup. Some 200 factories in the area will be relocated.

By 1919, hail cannons had been discredited—but people intent on changing the weather refuse to give them up.