Hiatus of Global Warming: A Review

The slowdown in the global mean surface temperature (GMST) warming over the past decade or so,referred to as the global warming "hiatus",has attracted wide attention and also cast public doubt on global warming.Great efforts have been made to verify the global warming hiatus,as well as its causes and influences.This paper reviews and summarizes results of recent researches on the global warming hiatus.It is generally accepted that the GMST warming tendency is slowing down recently.So far,proposed reasons to explain the hiatus include:the prolonged solar minimum,the increase in anthropogenic and natural aerosol emissions,and changes in ocean heat storage/re-distribution.Particularly,the increased ocean heat storage below 700 m has been identified during the global warming hiatus.Most of the models participating the Coupled Model Intercomparison Project Phase 5 failed to capture the global warming hiatus and therefore overestimated the observed trend in GMST.One general consensus is that natural climate variability instead of the external forcing caused the recent global warming hiatus.It is argued that the global warming hiatus would likely stop within several years or several decades,depending on the transition of the Pacific Decadal Oscillation.If the radiative forcing of the greenhouse gases continues to intensify,an apparent increase in GMST would be expected in future.We suggest that future research related to the global warming hiatus should focus on:(1) more accurate estimation of the GMST and the ocean heat content;(2) better understanding of the transition of decadal and multi-decadal (Pacific and Atlantic) oscillations;(3) uptake of energy stored in deep oceans and its impact on regional climate.