Strengthening of ocean heat uptake efficiency associated with the recent climate hiatus

Abstract

[1] The rate of increase of global-mean surface air temperature (SAT g ) has apparently slowed during the last decade. We investigated the extent to which state-of-the-art general circulation models (GCMs) can capture this hiatus period by using multimodel ensembles of historical climate simulations. While the SAT g linear trend for the last decade is not captured by their ensemble means regardless of differences in model generation and external forcing, it is barely represented by an 11-member ensemble of a GCM, suggesting an internal origin of the hiatus associated with active heat uptake by the oceans. Besides, we found opposite changes in ocean heat uptake efficiency (k), weakening in models and strengthening in nature, which explain why the models tend to overestimate the SAT g trend. The weakening of k commonly found in GCMs seems to be an inevitable response of the climate system to global warming, suggesting the recovery from hiatus in coming decades.

Recent slowdown of tropical upper tropospheric warming associated with Pacific climate variability

“…In contrast to the Anthro effect, the Nat effect contributes to this pattern including the CP cooling (Figure 3c). The recent years can be characterized by the global surface warming hiatus associated with sea surface cooling in the tropical Pacific [Trenberth and Fasullo, 2013;Watanabe et al, 2013Watanabe et al, , 2014. Figures 3b and 3d show changes in the SST prescribed in the ALL-run and Nat-run, respectively.…”

“…The variations of global surface air temperature (SAT) since the late 1990s can be characterized by the slowdown of the global mean SAT increase (called a "hiatus") associated with sea surface cooling in the tropical Pacific [Kosaka and Xie, 2013;Trenberth and Fasullo, 2013;Watanabe et al, 2013Watanabe et al, , 2014England et al, 2014]. Watanabe et al [2013Watanabe et al [ , 2014 revealed that the CMIP5 multi-AOGCM mean shows an apparent overestimation of the global mean SAT since the late 1990s resulting from the SST bias in the tropical Pacific.…”

“…Watanabe et al [2013Watanabe et al [ , 2014 revealed that the CMIP5 multi-AOGCM mean shows an apparent overestimation of the global mean SAT since the late 1990s resulting from the SST bias in the tropical Pacific. Sensitivity experiments conducted by Watanabe et al [2014] have suggested that recent fluctuations of the tropical Pacific SST and the resultant global warming hiatus are caused mainly by natural variability without anthropogenic influence.…”

Quantifying the likelihood of a continued hiatus in global warming

“…Mechanisms proposed to explain the hiatus include aerosol emissions from modest volcanic eruptions 6,12,13,16,23 , a delayed response to the Mount Pinatubo eruption 24 , the unexpectedly prolonged solar minimum 7,14,24 , stratospheric water vapour changes 15 , increases in anthropogenic sulfate aerosol emissions 14,16,25 , internal decadal variability in the Pacific and/or high-latitude oceans 9-11, 26, 27 , and externally forced and/or internally generated wind-driven rearrangement of heat in the oceans 4,5 . Several studies have previously commented on the likelihood of a warming hiatus and the potential for a subsequent accelerated warming 5,8,17,20,27,28 ; however, none have considered the likelihood of the present hiatus continuing into the future using the framework of conditional probabilities.…”

Heaving modes in the world oceans

“…Over the past several decades, the global sea surface temperature (SST) kept increasing; in addition, there are decadal variability of global ocean heat content, e.g., Levitus et al (2005Levitus et al ( , 2009Levitus et al ( , 2012, Easterling and Wehner (2009), Katsman and van Oldenborgh (2011), Kaufmann et al (2011), Guemas et al (2013), Watanabe et al (2013). However, ocean warming is far from uniform.…”