Science

Drought lowered earth's ability to absorb carbon: study

New data from the National Oceanic and Atmospheric Administration suggests weather phenomenon such as a drought can greatly diminish the Earth's ability to absorb carbon.

A terrible drought that shrivelled crops and farmer's incomes from Canada to Mexico in 2002also slashed the earth's ability to absorb carbon by half, new data suggests.

The National Oceanic and Atmospheric Administration has just released the first data from Carbon Tracker, a new modelling system designed to allow researchers to figure out how much carbon goes up into the atmosphere, how much comes down, and where it ends up.

Thedata showsthat during the North American drought in 2002, the soil, trees, crops and grasslands could absorb only half of the usual amount of carbon.

Normally, the continent's natural carbon sinks— the terrestrial ecosystem— absorb approximately 650 million metric tonnes of carbon from the atmosphere. That's about one-third of the total North American emissions fromhuman and natural sources.

The study, published online by the Proceedings of the National Academy of Sciences, shows that in 2002, the amount the sinks absorbed plummeted to 320 million metric tonnes. That left the equivalent of the yearly emissions from more than 200 million cars in the atmosphere.

Wouter Peters, lead author of the study, said the data show that just as greenhouse gases are believed to produce climate extremes, "the reverse is also true. Climate extremes can have a major impact on the amount of carbon dioxide in Earth's atmosphere."

The study wasa product of a collaboration among NOAA, Environment Canada, and several other institutions. Researchersmade more than 28,000 observations, capturing air in flasks at thetop of 10-metre poles and shipping them every week to NOAA for analysis. By comparing the concentration of CO2, the scientistsinferred how much carbonthe Earth's sinks were absorbing.

Droughts leave fewer plants to absorb carbon dioxide.In another example of the effect, aheat wave and drought in Europe in 2003 left more than 500 million metric tons of carbon in the atmosphere.

It is a classic positive feedback scenario, said co-author Andy Jacobson of NOAA.

"If warming causes drought, and droughts end up releasing more carbon, and carbon causes warming, that's a positive feedback cycle that can get pretty scary."

Understanding how much carbon the natural sinks can absorb is key to anticipating the effects of climate change. At the moment, the earth's natural sinks absorb about half of the carbon released by burning fossil fuels, but the study points out that those emissions are rising rapidly. As they rise, so do the dangers of other positive feedbacks, such as the release oflarge carbon reservoirs buried beneath the permafrost.

The long-term goal of Carbon Tracker is to be able to track the source of carbon emissions precisely, Jacobson said. This will be essential in an era of regulations on carbon emissions.

"There will need to be a verification system in place," he said. "You're not going to hide anything. If you put it into the atmosphere, it's going to be seen eventually, all around the world."

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