The cause of the pause

摘要

After a rise of 0.5℃ in the 25 years starting in the mid-1970s, the change in Earths global mean surface temperature has been close to zero since the turn of the century (Fig. 1). This hiatus in global warming has occurred despite retreating Arctic sea ice and rising sea levels. On page 403 of this issue, Kosaka and Xie make a strong case for the hypothesis that this hiatus is driven by the equatorial Pacific. Although the rise in carbon dioxide and other greenhouse gases explains many aspects of the overall warming trend over the past century (including the heat uptake by the oceans and the spatial and seasonal patterns of the warming), it cannot explain the multi-decadal fluctuations superimposed on this trend (Fig. 1). Forcing agents such aS"anthropogenic and volcanic aerosols and variations in the Sun's energy output are often called on to explain these features. Internal fluctuations of the atmosphere-ocean system, the low-frequency tail of our chaotic weather, could also be responsible. It is likely that both forced and internal variations have a role.