The authors report that over the last 50 years the average fraction of global CO2 emissions that remained in the atmosphere each year was around 43 per cent - the rest was absorbed by the Earth's carbon sinks on land and in the oceans. During that time the fraction has likely increased from 40 per cent to 45 per cent, suggesting a decrease in the efficiency of the natural sinks. The team also offers evidence that the sinks are responding to climate change and variability.
According to the research, CO2 emissions from fossil fuel between 2000 and 2008 rose 29 percent, and in spite of the global economic downturn emissions increased by 2 percent during 2008. The use of coal as a fuel has now surpassed oil and developing countries now emit more greenhouse gases than developed countries – with a quarter of their growth in emissions accounted for by increased trade with the West.
"The only way to control climate change is through a drastic reduction in global CO2 emissions. The Earth's carbon sinks are complex and there are some gaps in our understanding, particularly in our ability to link human-induced CO2 emissions to atmospheric CO2 concentrations on a year-to-year basis. But, if we can reduce the uncertainty about the carbon sinks, our data could be used to verify the effectiveness of climate mitigations policies," said Lead author Prof Corinne Le Quéré of the University of East Anglia.
The researchers called for more work to be done to improve our understanding of the land and ocean CO2 sinks, so that global action to control climate change can be independently monitored.
The sinks have a major influence on climate change and are important in understanding the link between anthropogenic CO2 emissions and atmospheric CO2 concentration. But so far scientists have not been able to calculate the CO2 uptake of the sinks with sufficient accuracy to explain all the annual changes in atmospheric CO2 concentration, which hinders the scientists' ability to monitor the effectiveness of CO2 mitigation policies.
Citation: Corinne Le Quéré, Michael R. Raupach, Josep G. Canadell, Gregg Marland et al,
'Trends in the sources and sinks of carbon dioxide', Nature Geoscience online, 2009, doi:10.1038/ngeo689