Approximately half of the CO₂ emitted by fossil fuel burning remains in the atmosphere; the rest is absorbed by the ocean or incorporated by the terrestrial biosphere in roughly equal measures. Two studies reassess the uptake of CO₂ by these sinks (see the Perspective by Baker). In order to understand the relative role of different parts of the terrestrial biosphere as carbon sinks, global measurements of atmospheric CO₂ concentration must be interpreted by "inversion" models to determine how uptake, emission, and transport contribute to the seasonal and regional differences. Previous studies have suggested that there must be a strong carbon sink in the Northern Hemisphere, and that the tropics are a net carbon source. Stephens et al. (p. 1732) report that global vertical distributions of CO₂ in the atmosphere are not consistent with that interpretation but are more consistent with models that show a smaller Northern Hemispheric carbon sink and possibly strong carbon uptake in the tropics. The rate of uptake of CO₂ depends on the difference between the partial pressure of CO₂ in the atmosphere and that which would exist if the ocean and the atmosphere were at equilibrium. Le Quéré et al. (p. 1735, published online 17 May) report that the rate of uptake by Southern Ocean, one of the most important CO₂-absorbing regions, has slowed relative to what would be expected based solely on how fast the concentration of atmospheric CO₂ has risen since 1981. They attribute this shortfall to an increase in windiness over the Southern Ocean that increases the outgassing of natural CO₂. The increased windiness has also been ascribed to human activity, and the authors predict that this relative trend will continue.