Was the global warming hiatus caused by warming in the deep ocean?

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Monday, 5 January 2015: 12:00 AM
122BC (Phoenix Convention Center - West and North Buildings)
Josh Willis, JPL, Pasadena, CA; and N. Loeb, W. Llovel, and V. Nieves

Anthropogenic greenhouse gases trap excess heat on the Earth, but where does it go? Atmospheric warming, ice melt, land warming, and vaporization of water combined account for less than 10 percent of this excess heat. The world's oceans are such dominant sources of heat storage that ocean warming can be used as a direct metric for the net radiative forcing of the climate system. Furthermore, the rate of globally averaged surface temperature is closely tied to top 100 meter layer of the ocean. This is illustrated by the fact that El Nino and La Nina—natural climate cycles of the ocean—strongly influence the year to year change in global surface temperature. Recent work has suggested that the relatively low rate of global surface warming since the late 1990s is somehow related to the response of the ocean and its uptake of heat. Studies based on ocean reanalyses have suggested that the oceans are taking up heat faster in the deeper layers and that the warming “hiatus” is a direct result of deep ocean warming. Here we consider the observational evidence for a connection between ocean warming and the hiatus. Satellite observations of sea level rise, as well as ocean mass increase from GRACE provide an indirect measure of ocean warming. In addition, we consider ocean warming estimates based on the Argo array of profiling floats and other in situ observations of ocean temperature change over the past 20 years. We find little evidence in these data that the most recent decade has seen warming in the deep layers of the ocean at faster rates than previous decades. In the top 300 m, we find that the most recent decade shows less warming than the previous decade. Below this, there is little evidence for any change in the warming rate. We also update comparisons with estimates of ocean warming and the net radiative imbalance based on CERES satellite observations.