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A new look at the “global warming hiatus” as a redistribution of energy in the Earth’s system

Atmospheric greenhouse gases have continued their steady increase in the new century. Logically, one would expect that global mean surface temperature (GMST) would also continue to increase in the same fashion as experienced in the latter decades of the 20th century. However, between 1998 and 2013 GMST actually plateaued with much smaller increases than the average over the last 60 years and labeled the “global warming hiatus.” The fact that this slowdown in GMST increase was not predicted by most climate models has led some to question the steady increase in heat predicted under increased greenhouse gas conditions.

Ocean heat content over the past 60 years
Yearly ocean (black) and atmosphere (blue) heat content anomaly (data from IPCC AR5 report) shows the vast amount of heat absorbed by the ocean compared to the atmosphere. Ocean heat content combines upper and deep ocean heat content values for each year from that report.

A new paper in Earth’s Future documents the work of many researchers showing that GMST, while an important climate indicator, is a measure of the Earth’s surface warming, not a measure of total accumulated heat energy in the Earth’s system. The paper notes that the amount of missing heat that could cause the slowdown in GMST increase would be but a small fraction of the total heat entering the ocean. So the slowdown in GMST increase is most likely a redistribution of excess heat into and within the ocean. Thus, the overall Earth continued to warm with the ocean absorbing the large majority of excess heat. Present and future research activities are interested in where and under what conditions the ocean experienced increased heat uptake. An important component in achieving this is support of the subsurface ocean observing system – mainly by Argo profiling floats, both in its present form and with more complete global coverage – and subsurface remote sensing. Improvements in modeling ocean heat uptake are possible and already underway.

Written by
Tim Boyer (NOAA National Centers for Environmental Information), Veronica Nieves (NASA Jet Propulsion Laboratory and the University of California, Los Angeles), and Xiao-Hai Yan (University of Delaware)

Xiao-Hai Yan1, Tim Boyer2, Kevin Trenberth3, Thomas R. Karl4, Shang-Ping Xie5, Veronica Nieves6, Ka-Kit Tung7, and Dean Roemmich5

1U. Delaware

2NOAA National Centers for Environmental Information

3National Center for Atmospheric Research

4Independent Consultant

5Scripps Institution of Oceanography

6NASA Jet Propulsion Laboratory and the University of California, Los Angeles

7U. Washington