International study calculates Earth's 'breathing' rate

July 8, 2010

    Earth's plants inhale 123 billion tonnes of carbon through photosynthesis each year, according to an international study co-authored by McMaster's Altaf Arain.

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Earth's plants inhale 123 billion tonnes of carbon through photosynthesis each year, according to an international study co-authored by McMaster's Altaf Arain.

The report, published in the journal Science, represents the first time researchers have arrived at such a conclusion based on large numbers of measurements taken across the globe rather than computer modeling. According to Arain, the study will help researchers improve predictive models as well as better understand how climate change might affect the carbon cycle in the future.

"In the past, numbers such as these were considered hypotheticals," said Arain, the director of the McMaster Centre for Climate Change. "We now have measurement-based estimates that will help us to better understand terrestrial carbon cycle."

The team measured carbon dioxide and water exchanges at a network of more than 250 measurement sites, known as FLUXNET, located around the world, between 1998 and 2006. Arain was in charge of measurement stations located at Turkey Point near Lake Erie in Ontario.

The researchers found that most carbon dioxide uptake takes place in tropical forests and savannas. They also found that water availability plays an important role in how much carbon is stored by plants through photosynthesis (the process by which plants take in carbon dioxide and store it as sugars).The study found that 40 per cent of vegetation land, and 50 per cent of croplands are sensitive to the amount of rainfall they receive, having serious implications for global food security.

In a second paper published in the same issue of Science these researchers estimated that ecosystem respiration sensitivity to temperature for various ecosystems across the world is independent of average annual temperature in the region and that this sensitivity does not differ among various ecosystems.

"This means that respiration of various ecosystems (including tropical, temperate and high latitude ecosystems) intensifies to the same extent when temperature becomes warmer," Arain said.

"These are two of the most significant papers the centre has collaborated on since its opening in March. It really underscores the importance of the work that we're doing. It's a really great thing for the climate centre and for McMaster."

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