Oceans absorbing less CO2

A decline in the proportion of carbon dioxide (CO2) emissions absorbed by land and oceans is speeding up the growth of atmospheric CO2, according to a paper published 23 October 2007 in the US Journal: Proceedings of the National Academy of Science.

Lead author and Executive Director of the Global Carbon Project, CSIRO’s Dr Pep Canadell, says the acceleration is due to three factors: global economic growth; the world’s economy becoming more carbon intense (that is, since 2000 more carbon is being emitted to produce each dollar of global wealth); and a deterioration in the land and oceans’ ability to absorb carbon from the atmosphere at the required rate.

“What we are seeing is a decrease in the planet’s ability to absorb carbon emissions due to human activity,” Dr Canadell says.

“Fifty years ago, for every tonne of CO2 emitted, 600kg were removed by land and ocean sinks. However, in 2006, only 550kg were removed per tonne and that amount is falling.”

Dr Canadell says the results have major implications for the current and future growth of atmospheric CO2.

“The majority of current emission scenarios for modelling climate through the 21st century assume sustained decreases in the carbon intensity of the global economy, which have not occurred since 2000,” he says.

CSIRO’s Dr Mike Raupach, a co-chair of the Global Carbon Project, says “The carbon cycle is generating stronger-than-expected and sooner-than-expected climate ‘forcing’ –  that is, mechanisms that ’force‘ the climate to change. In turn, climate change itself is feeding back to affect the carbon cycle, decreasing land and ocean sinks."

Most of the co-authors of the study – including Dr Canadell and Dr Raupach – are members of the UN Intergovernmental Panel on Climate Change which was awarded the Nobel Peace Prize for 2007 earlier this month.

Dr Raupach says the research shows that the Earth is losing its restorative capacity to absorb CO2 emissions following massive increases in emissions over the past half century. “The longer we delay reducing emissions, the more restorative capacity will be lost,” Dr Raupach says. 

Editor's Note: Original news release can be found here.