Clim. Dynam. http://doi.org/r8h (2014)

Temperature differences between the land and the sea influence interdecadal variability of large-scale circulation and atmospheric blocking — near-stationary pressure fields. Yongli He and colleagues, at Lanzhou University, China investigate this relationship and its impact on enhanced winter warming in the Northern Hemisphere.

They define a land–sea index for December to February (Northern Hemisphere winter), which is defined by the temperature anomaly of the North Pacific Ocean and Labrador Sea compared with sections of Russia and North America respectively. The index shifted from a negative to a positive anomaly in the 1980s; that is, land has warmed to a greater extent than the sea. However, since the 2000s there has been a decrease in the index.

A positive index weakens planetary wave activity — high-altitude wind meanders — altering circulation and reducing the chance of blocking as it favours westerly wind acceleration. These changes could strengthen the cold-ocean/warm-land pattern (positive index), and increase regional warming.