Thursday, October 03, 2013

Sea level rise demonstrates continued global warming

One of the most telling little figures that I've come across in the new IPCC report is this Chapter 3 comparison (Fig. 3.21) of changes in human-derived carbon dioxide in the oceans, global mean sea level and global mean upper ocean heat content since 1950. From the report:

The consistency between the patterns of change in a number of independent ocean parameters enhances confidence in the assessment that the physical and biogeochemical state of the oceans has changed.... High agreement among multiple lines of evidence based on independent data and different methods provides high confidence in the observed increase in these global metrics of ocean change

The oceans show that global warming has continued apace. The lack of a slowdown in the rate of sea level change is of particular interest given the media coverage devoted to the perceived slowdown in the rate of surface temperature change. Since >90% of the excess heat in the climate system goes into the ocean, and a warmer ocean should expand, sea level rise is a good metric for tracking changes in the overall heat in the climate system. From a great summary by G. Bala:

Sea level rise is probably a powerful metric that integrates both the ocean heat content as well as the melt in the cryosphere as sea level rise is due to both the thermal expansion of the oceans from heating and the melt waters from glaciers and ice sheets... It is time for IPCC to recommend and encourage climate change discussions that are centred on integrated measures of climate change such as ocean heat content and sea level rise to avoid confusion.  Alternatively, if we want to continue our discussions centred on surface temperature changes, it makes scientific sense to focus on 30-yr trends.

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