Quantifying the likelihood of a continued hiatus in global warming

Since the end of the twentieth century, global mean surface temperature has not risen as rapidly as predicted by global climate models(1-3) (GCMs). This discrepancy has become known as the global warming 'hiatus' and a variety of mechanisms(1,4-17) have been proposed to explain the observed slowdown in warming. Focusing on internally generated variability, we use pre-industrial control simulations from an observationally constrained ensemble of GCMs and a statistical approach to evaluate the expected frequency and characteristics of variability-driven hiatus periods and their likelihood of future continuation. Given an expected forced warming trend of similar to 0.2 K per decade, our constrained ensemble of GCMs implies that the probability of a variability-driven 10-year hiatus is similar to 10%, but less than 1% for a 20-year hiatus. Although the absolute probability of a 20-year hiatus is small, the probability that an existing 15-year hiatus will continue another five years is much higher (up to 25%). Therefore, given the recognized contribution of internal climate variability to the reduced rate of global warming during the past 15 years, we should not be surprised if the current hiatus continues until the end of the decade. Following the termination of a variability-driven hiatus, we also show that there is an increased likelihood of accelerated global warming associated with release of heat from the sub-surface ocean and a reversal of the phase of decadal variability in the Pacific Ocean.