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Diagnosing Causes of Sea Level Rise

Filed under: — eric @ 8 January 2015

Guest post by Sarah G. Purkey and Gregory C. Johnson,
University of Washington / NOAA

I solicited this post from colleagues at the University of Washington. I found their paper particularly interesting because it gets at the question of sea level rise from a combination of ocean altimetry and density (temperature + salinity) data. This kind of measurement and calculation has not really been possible — not at this level of detail — until quite recently. A key finding is that one can reconcile various different estimates of the contributions to observed sea level rise only if the significant warming of the deep ocean is accounted for. There was a good write-up in The Guardian back when the paper came out.– Eric Steig


Sea leave rise reveals a lot about our changing climate. A rise in the mean sea level can be caused by decreases in ocean density, mostly reflecting an increase in ocean temperature — this is steric sea level rise. It can also be caused by an increase in ocean mass, reflecting a gain of fresh water from land. A third, and smaller, contribution to mean sea level is from glacial isostatic adjustment. The contribution of glacial isostatic adjustment, while small, has a range of possible values and can be a significant source of uncertainty in sea level budgets. Over recent decades, very roughly half of the observed mean sea level rise is owing to changes in ocean density with the other half owing to the increased in ocean mass, mostly from melting glaciers and polar ice sheets. The exact proportion has been difficult to pin down with great certainty. More »

References

  1. S.G. Purkey, G.C. Johnson, and D.P. Chambers, "Relative contributions of ocean mass and deep steric changes to sea level rise between 1993 and 2013", Journal of Geophysical Research: Oceans, vol. 119, pp. 7509-7522, 2014. http://dx.doi.org/10.1002/2014JC010180

Unforced Variations: Jan 2015

Filed under: — group @ 7 January 2015

This month’s open thread. Sorry for the slow start – you know what it’s like after the holidays…

Absolute temperatures and relative anomalies

Filed under: — gavin @ 23 December 2014

Most of the images showing the transient changes in global mean temperatures (GMT) over the 20th Century and projections out to the 21st C, show temperature anomalies. An anomaly is the change in temperature relative to a baseline which usually the pre-industrial period, or a more recent climatology (1951-1980, or 1980-1999 etc.). With very few exceptions the changes are almost never shown in terms of absolute temperatures. So why is that?

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Clarity on Antarctic sea ice.

Filed under: — eric @ 19 December 2014

I’ve always been a skeptic when it comes to Antarctic sea ice. I’m not referring here to the tiresome (and incorrect) claim that the expansion of sea ice around Antarctica somehow cancels out the dramatic losses of sea ice in the Arctic (NB: polar bears don’t really care if there is sea ice in Antarctica or not). Rather, I’m referring to the idea that the observation of Antarctic sea ice expansion represents a major conundrum in our understanding of the climate system, something one hears even from knowledgeable commentators. In this post, I’ll try to provide some clarity on this subject, with some basic background and discussion of a couple of important recent papers.
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AGU 2014

Filed under: — group @ 14 December 2014

Once more unto the breach!

Fall AGU this year will be (as last year)

…the largest Earth Science conference on the planet, and is where you will get previews of new science results, get a sense of what other experts think about current topics, and indulge in the more social side of being a scientist.

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