Drought’s Impact on Carbon Cycle Equal to Millions of Cars

Drought map of the U.S.Anyone who keeps up with the science of global warming knows that carbon dioxide alone isn’t the problem. Besides that and the other greenhouse gases (methane and nitrous oxide, for instance) we spew into the atmosphere, there’s also the threat of feedback loops and other mechanisms that could magnify the impact of those pollutants even more.

One of those mechanisms, it turns out, is drought. Which is a real cause for concern, considering how much of the U.S. and other regions of the globe are seeing record-breaking dry weather year after year.

The National Oceanic and Atmospheric Administration (NOAA) this week announced that, using data from its CarbonTracker modeling system, the North American drought in 2002 had as bad an impact on the atmosphere as year’s worth of emissions from 200 million cars.

During 2002, some 45 percent of the U.S. alone experienced “extreme” or “exceptional” drought. Drought means less water for healthy soils, plants and trees, which is bad for global warming because soils, plants and trees are natural carbon sinks. Under normal conditions, they take up about one-third of the carbon dioxide we in the States pump into the air every year. But not during droughts.

The 2002 drought reduced the effectiveness of North America’s natural carbon sinks by half, according to NOAA. That meant that 320 million of the 650 million metric tons of carbon dioxide normally absorbed by vegetation and soil stayed in the air instead.

Considering this year’s drought conditions, it’s likely we’ll soon be hearing similar stats for 2007 carbon absorption rates. As of the end of October, for example, a full two-thirds of the southeastern U.S. was in “moderate” to “exceptional” drought. Parts of Australia, China, South America and southern Africa were also experiencing exceptional drought conditions.

The impact on natural carbon sinks is a concern because it could nullify any actions we take to cut greenhouse gas emissions, according to Wouter Peters, the scientist who led the NOAA study.

“Disruptions to natural carbon uptake can have enormous environmental and economic effects, possibly even erasing efforts to reduce fossil fuel emissions in a given year,” Peters said. “Climate extremes can have a major affect on the amount of carbon dioxide in Earth’s atmosphere.”

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