Changes in the phase of the annual cycle of surface temperature.

The annual cycle in the Earth's surface temperature is extremely large-comparable in magnitude to the glacial-interglacial cycles over most of the planet. Trends in the phase and the amplitude of the annual cycle have been observed, but the causes and significance of these changes remain poorly understood-in part because we lack an understanding of the natural variability. Here we show that the phase of the annual cycle of surface temperature over extratropical land shifted towards earlier seasons by 1.7 days between 1954 and 2007; this change is highly anomalous with respect to earlier variations, which we interpret as being indicative of the natural range. Significant changes in the amplitude of the annual cycle are also observed between 1954 and 2007. These shifts in the annual cycles appear to be related, in part, to changes in the northern annular mode of climate variability, although the land phase shift is significantly larger than that predicted by trends in the northern annular mode alone. Few of the climate models presented by the Intergovernmental Panel on Climate Change reproduce the observed decrease in amplitude and none reproduce the shift towards earlier seasons.

Observational contrains on the global atmospheric co2 budget.

Observed atmospheric concentrations of CO(2) and data on the partial pressures of CO(2) in surface ocean waters are combined to identify globally significant sources and sinks of CO(2). The atmospheric data are compared with boundary layer concentrations calculated with the transport fields generated by a general circulation model (GCM) for specified source-sink distributions. In the model the observed north-south atmospheric concentration gradient can be maintained only if sinks for CO(2) are greater in the Northern than in the Southern Hemisphere. The observed differences between the partial pressure of CO(2) in the surface waters of the Northern Hemisphere and the atmosphere are too small for the oceans to be the major sink of fossil fuel CO(2). Therefore, a large amount of the CO(2) is apparently absorbed on the continents by terrestrial ecosystems.