ScienceDaily (July 5, 2010) Two recent international studies are poised to change the way scientists view the crucial relationship between Earth’s climate and the carbon cycle. These reports explore the global photosynthesis and respiration rates — the planet’s deep “breaths” of carbon dioxide, in and out — and researchers say that the new findings will be used to update and improve upon traditional models that couple together climate and carbon.
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The two reports will be published online by the journal Science at the Science Express Web site on July 5. Science is published by AAAS, the nonprofit science society.
Christian Beer from the Max Planck Institute for Biogeochemistry in Jena, Germany, along with colleagues from 10 other countries around the world, first take a look at Earth’s Gross Primary Production, or GPP, which represents the total amount of carbon dioxide that terrestrial plants breathe in through photosynthesis each year. With a novel combination of observations and modeling, they estimate the total amount of carbon dioxide that the world’s plant life inhales annually to be 123 billion tons.
Then, Miguel Mahecha, also from the Max Planck Institute for Biogeochemistry, and another international team of researchers settle a long-standing debate over the effects of short-term variations in air temperature on ecosystem respiration, or the Earth’s exhalation of carbon dioxide back into the atmosphere. They show that the sensitivity of ecosystem respiration to short-term variations in temperature is similar around the world. The researchers also suggest that factors other than temperature, such as the slow, ongoing transformations of carbon in the soil and water availability, appear to play crucial roles in long-term ecosystem carbon balances.
Together, these findings shed more light on the global cycle of carbon into and out of the atmosphere and how those processes are coupled with Earth’s ever-changing climate. The researchers analyzed vast amounts of climate and carbon data from around the world, and they say their results should help to improve the validity of predictive models and help resolve how climate change might affect the carbon cycle — and our world — in the future.
“An understanding of the factors that control the GPP of various terrestrial ecosystems is important because we humans make use of many ecosystem services, such as wood, fiber, and food,” said Beer. “Additionally, such an understanding is important in the context of climate change as a consequence of carbon dioxide emissions from burning fossil fuels because vegetation greatly modulates the land-atmosphere exchanges of greenhouse gases, water, and carbon dioxide…”
In their report, Beer and his colleagues pooled large amounts of data from FLUXNET, an international initiative established more than 10 years ago to monitor exchanges of carbon dioxide between Earth’s ecosystems and the atmosphere, with remote sensing and climate data from around the world to calculate the spatial distribution of mean annual GPP between 1998 and 2006.
The researchers highlight the fact that uptake of carbon dioxide is most pronounced in the planet’s tropical forests, which are responsible for a full 34 percent of the inhalation of carbon dioxide from the atmosphere. Savannas then account for 26 percent of the global uptake, although the researchers note that savannas also occupy about twice as much surface area as tropical forests.
Precipitation also plays a significant role in determining the gross global carbon dioxide uptake, the researchers found. They suggest that rainfall has a significant influence on the amount of carbon that plants utilize for photosynthesis on more than 40 percent of vegetated lands, a discovery that stresses the importance of water availability for food security. According to the study, climate models often show great variation, and some of them overestimate the influence of rainfall on global carbon dioxide uptake.
“We reached a milestone with this paper by using plenty of data from FLUXNET in addition to remote sensing and climate reanalysis,” Beer said. “With our estimation of global GPP, we can do two things — compare our results with
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