The role of sea surface temperature variability in changes to global surface air temperature related to two periods of warming slowdown since 1940

Over the last century, the global mean surface air temperature (SAT) has experienced two periods of warming slowdown (hiatuses), namely 1940-1975 and 1998-2012, as well as showing well-defined interdecadal oscillations. Previous studies have focused mainly on the most recent hiatus, and little is known about the period between 1940 and 1975. From the point of view of the sea surface temperature (SST), there are two aspects of interest; i.e., the climatological SST and SST variability. In this paper, observational and modelling evidence is used to show that, compared with the climatological SST, SST variability has been the main cause of the slowdown in rate of increase in SAT since 1940. In addition, the observational data and simulation results show that SST variability had a greater impact on the slowdown in rate of increase in SAT from 1940 to 1975 (- 1.2 x 10(-3) degrees C/year) than from 1998 to 2012 (- 5.7 x 10(-3) degrees C/year). The SAT change over the period 1940-1975 (1.0 x 10(-4) degrees C/year) was less affected by the climatological SST forcing experiment than that over the period 1998-2012 (- 5.0 x 10(-4) degrees C/year). Comparing with 1940-1975, the SAT change over the period 1998-2012 was much affected by the global SAT long-term warming. The distributions of wind stress and atmospheric pressure both indicate that, although the eastern Pacific Ocean played an important role in influencing the global SAT trend between 1998 and 2012, it made little contribution to changes in global SAT between 1940 and 1975. In addition, from the perspective of seasonality, the interdecadal variation of SAT over these two periods was a seasonally dependent phenomenon. Over the period 1940-1975, the annual SAT trend essentially followed the summer SAT trend, whereas between 1998 and 2012, winter was the dominant season of annual SAT change.