Carbon sink slowdown contributing to rapid growth in atmospheric CO2

There has been a decline in the efficiency of natural land and ocean sinks which soak up carbon dioxide (CO2) emitted to the atmosphere by human activities, according to findings published this week in the Proceedings of the National Academy of Sciences of the US (PNAS). The swift increase in atmospheric CO2 is due to faster economic growth coupled with a halt in carbon intensity reductions, in addition to natural sinks removing a smaller proportion of emissions from the air. Carbon intensity is the amount of carbon emitted to produce one dollar of global wealth.

The study's lead author, Dr Pep Canadell, executive director of the Global Carbon Project, explained 'Fifty years ago, for every tonne of CO2 emitted, 600 kg were removed by natural sinks. In 2006 only 550 kg were removed per tonne and that amount is falling.' 'In addition to the growth of global population and wealth, we now know that significant contributions to the growth of atmospheric CO2 arise from the slow down of natural sinks and the halt to improvements in carbon intensity.'

The rise in growth in atmospheric CO2 is generating climate forcings that are bigger and sooner than expected. By altering the global energy balance, these mechanisms 'force' the climate to change.

'There are regional differences in the efficiency of natural sinks. Half of decline in the efficiency of the ocean sink is due to the intensification and poleward movement of the westerly winds in the Southern ocean,' said contributing author Corinne Le Quere of the University of East Anglia.

'The proportion of carbon dioxide remaining in the atmosphere after vegetation and the oceans absorb what they can has escalated over the past 50 years, showing a decrease in the planet's ability to absorb anthropogenic emissions.' said Dr Canadell.

Dr Raupach, co-chair of the Global Carbon Project, said 'We have found that the earth is losing its restorative capacity to absorb CO2 emissions in the face of the massive increases in emissions over the last half century. The longer we delay reducing emissions, the more restorative capacity will be lost.'

The majority of these authors are members of the Intergovernmental Panel on Climate Change which was recently awarded the Nobel Peace Prize 2007.