The University of Bristol in the UK has published a study based not on climate modeling, but on statistical analysis of data including historical data from Antarctic ice cores.
The study shows that the balance between the airborne and the absorbed fraction of carbon dioxide has stayed approximately constant since 1850, despite emissions of carbon dioxide having risen from about 2 billion tons a year in 1850 to 35 billion tons a year now. This suggests that terrestrial ecosystems and the oceans have a much greater capacity to absorb CO2 than had been previously expected.