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Tropical SSTs: Natural variations or Global warming?

Filed under: — group @ 11 September 2006

by Michael Mann and Gavin Schmidt

Roughly a year ago, we summarized the state of play in the ongoing scientific debate over the role of anthropogenic climate change in the observed trends in hurricane activity. This debate (as carefully outlined by Curry et al recently) revolves around a number of elements – whether the hurricane (or tropical cyclone) data show any significant variations, what those variations are linked to, and whether our understanding of the physics of tropical storms is sufficient to explain those links.

Several recent studies such as Emanuel (2005 — previously discussed here) and Hoyos et al (2006 — previously discussed here) have emphasized the role of increasing tropical sea surface temperatures (SSTs) on recent increases in hurricane intensities, both globally and for the Atlantic. The publication this week of a comprehensive paper by Santer et al provides an opportunity to assess the key middle question – to what can we attribute the relevant changes in tropical SSTs? And in particular, what can we say about Atlantic SSTs where we have the best data? More »

Reactions to tighter hurricane intensity/SST link

Filed under: — gavin @ 20 March 2006

There was another twist to the hurricanes/global warming issue in Science Express on Friday where a new paper from the Webster/Curry team just appeared. This study, lead by Carlos Hoyos, crosses a few t’s and dots a couple of i’s on the connection of increasing numbers of intense hurricanes (Cat. 4 and 5) to sea surface temperatures (SST). Basically, they looked at a number of other key variables for hurricane intensity (like wind shear and humidity) and examined whether there was any pattern to those variables across the different ocean basins that they study. Bottom line? None of the other variables have as much explanatory power for the long term trends as SST which is the only consistently trending constituent in the mix. So far, so un-surprising. However, one interesting aspect of this story is that almost all the key players in the ongoing debate were interviewed by different journalists in various media and those comments are probably more useful for gauging the state of play than the details of the new paper itself. More »

A hypothesis about the cold winter in eastern North America

Filed under: — stefan @ 30 March 2015

The past winter was globally the warmest on record. At the same time it set a new cold record in the subpolar North Atlantic – and it was very cold in the eastern parts of North America. Are these things related?

Two weeks ago NOAA published the following map of temperature anomalies for the past December-January-February (i.e. the Northern Hemisphere winter). One week ago, we published a paper in Nature Climate Change (which had been in the works for a few years) arguing that the cold in the subpolar North Atlantic is indicative of an AMOC slowdown (as discussed in my last post). Immediately our readers started to ask (as we indeed had been asking ourselves): does the cold winter in eastern North America (culminating in the Inhofe snowball incident) have anything to do with what is going on in the Atlantic?

Winter15NOAAFig. 1 Temperature anomaly map for the past december-january-february, from NOAA.

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  1. S. Rahmstorf, J.E. Box, G. Feulner, M.E. Mann, A. Robinson, S. Rutherford, and E.J. Schaffernicht, "Exceptional twentieth-century slowdown in Atlantic Ocean overturning circulation", Nature Climate change, 2015.

What’s going on in the North Atlantic?

Filed under: — stefan @ 23 March 2015

The North Atlantic between Newfoundland and Ireland is practically the only region of the world that has defied global warming and even cooled. Last winter there even was the coldest on record – while globally it was the hottest on record. Our recent study (Rahmstorf et al. 2015) attributes this to a weakening of the Gulf Stream System, which is apparently unique in the last thousand years.

The whole world is warming. The whole world? No! A region in the subpolar Atlantic has cooled over the past century – unique in the world for an area with reasonable data coverage (Fig. 1). So what’s so special about this region between Newfoundland and Ireland?


Fig. 1 Linear temperature trend from 1900 to 2013. The cooling in the subpolar North Atlantic is remarkable and well documented by numerous measurements – unlike the cold spot in central Africa, which on closer inspection apparently is an artifact of incomplete and inhomogeneous weather station data.

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Severe Tropical Cyclone Pam and Climate Change

Filed under: — stefan @ 18 March 2015

Guest post by Kerry Emanuel

In the past 16 months, two exceptionally intense tropical cyclones, Haiyan and Pam, have struck the western Pacific with devastating effect. Haiyan may have had the highest wind speeds of any tropical cyclone on record, but we will never know for sure because we do a poor job estimating the intensity of storms that are not surveyed by aircraft. (Currently, only North Atlantic tropical cyclones are routinely reconnoitered by aircraft, and only if they threaten populated regions within a few days.) Pam’s analyzed intensity puts it within 10 knots of the most intense storms on record in the South Pacific, but here again this is within the error bars of satellite-derived intensity estimates.

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