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Millennia of sea-level change

How has global sea level changed in the past millennia? And how will it change in this century and in the coming millennia? What part do humans play? Several new papers provide new insights.

2500 years of past sea level variations

This week, a paper will appear in the Proceedings of the National Academy of Sciences (PNAS) with the first global statistical analysis of numerous individual studies of the history of sea level over the last 2500 years (Kopp et al. 2016 – I am one of the authors). Such data on past sea level changes before the start of tide gauge measurements can be obtained from drill cores in coastal sediments. By now there are enough local data curves from different parts of the world to create a global sea level curve.

Let’s right away look at the main result. The new global sea level history looks like this:


Fig. 1 Reconstruction of the global sea-level evolution based on proxy data from different parts of the world. The red line at the end (not included in the paper) illustrates the further global increase since 2000 by 5-6 cm from satellite data. More »


  1. R.E. Kopp, A.C. Kemp, K. Bittermann, B.P. Horton, J.P. Donnelly, W.R. Gehrels, C.C. Hay, J.X. Mitrovica, E.D. Morrow, and S. Rahmstorf, "Temperature-driven global sea-level variability in the Common Era", Proceedings of the National Academy of Sciences, vol. 113, pp. E1434-E1441, 2016.


Filed under: — rasmus @ 9 February 2016

Ross McKitrick was so upset about a paper ‘Learning from mistakes in climate research(Benestad et al., 2015) that he has written a letter of complaint and asked for immediate retraction of the pages discussing his work.

This is an unusual step in science, as most disagreements and debate involve a comment or a response to the original article. The exchange of views, then, provides perspectives from different angles and may enhance the understanding of the problem. This is part of a learning process.

Responding to McKitrick’s letter, however, is a new opportunity to explain some basic statistics, and it’s excellent to have some real and clear-cut examples for this purpose.

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  1. R.E. Benestad, D. Nuccitelli, S. Lewandowsky, K. Hayhoe, H.O. Hygen, R. van Dorland, and J. Cook, "Learning from mistakes in climate research", Theoretical and Applied Climatology, vol. 126, pp. 699-703, 2015.

Climate change is coming to a place near you

What are the local consequences of a continued global warming? And what kind of future climate can you expect for you children? Do we expect more extreme events, and will a global warming affect the statistics of storms? Another question is how the local changes matters for local communities and the ecosystem.

It may be contrary to most people’s impression. We have a clearer picture of future climate changes on a global scale than of the local consequences associated with a global warming. And we know why.

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A hypothesis about the cold winter in eastern North America + Update

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, vol. 5, pp. 475-480, 2015.

Limiting global warming to 2 °C – why Victor and Kennel are wrong + update

Filed under: — stefan @ 1 October 2014

In a comment in Nature titled Ditch the 2 °C warming goal, political scientist David Victor and retired astrophysicist Charles Kennel advocate just that. But their arguments don’t hold water.

It is clear that the opinion article by Victor & Kennel is meant to be provocative. But even when making allowances for that, the arguments which they present are ill-informed and simply not supported by the facts. The case for limiting global warming to at most 2°C above preindustrial temperatures remains very strong.

Let’s start with an argument that they apparently consider especially important, given that they devote a whole section and a graph to it. They claim:

The scientific basis for the 2 °C goal is tenuous. The planet’s average temperature has barely risen in the past 16 years. More »

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