Information from new data runs contrary to a significant body of recent research that expects the capacity of terrestrial ecosystems and the oceans to absorb CO2 should start to diminish as CO2 emissions increase, letting greenhouse gas levels skyrocket.

The data, however, shows the balance between the airborne and the absorbed fraction of carbon dioxide has stayed approximately constant since 1850.

That's despite emissions of carbon dioxide having risen from about 2 billion tons a year in 1850 to 35 billion tons a year now, according to the University of Bristol in the UK.

Dr Wolfgang Knorr at the University of Bristol has found that the trend in the airborne fraction since 1850 has only been 0.7pc per decade (standard deviation of 1.4pc), which is essentially zero.

The strength of the new study, published online on Nov 9 in Geophysical Research Letters, is that it rests solely on measurements and statistical data, including historical records extracted from Antarctic ice, and does not rely on computations with complex climate models, the university says.

This work is extremely important for climate change policy, because emission targets to be negotiated at the UN Climate Change Conference in Copenhagen early next month have been based on projections that have a carbon free sink already factored in.

Some researchers have cautioned against this approach, pointing at evidence that suggests the sink has already started to decrease.

* The paper's citation is: W. Knorr. 2009. Is the airborne fraction of anthropogenic CO2 emissions increasing? Geophysical Research Letters. 36: L21710, doi:10.1029/2009GL040613.