Science Source

Changes in the phase of the annual cycle of surface temperature

States 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
Shows 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
States this change is highly anomalous with respect to earlier variations, which we interpret as being indicative of the natural range
Observes significant changes in the amplitude of the annual cycle between 1954 and 2007
Finds 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
Notes 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