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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:

Kopp2016_Fig1a+sat

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 »

References

  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. http://dx.doi.org/10.1073/pnas.1517056113

What is the best description of the greenhouse effect?

Filed under: — rasmus @ 12 February 2016

What exactly is the greenhouse effect? And what does it look like if we view it from a new angle? Of course, we know the answer, and Raymond Pierrehumbert has written an excellent paper about it (Infrared radiation and planetary temperature). Computer code used in climate models contain all the details.

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Marvel et al (2015) Part III: Response to Nic Lewis

The first post in this series gave the basic summary of Marvel et al (2015) (henceforth MEA15) and why I think it is an important paper. The second discussed some of the risible immediate media coverage. But there has also been an ‘appraisal’ of the paper by Nic Lewis that has appeared in no fewer than three other climate blogs (you can guess which). This is a response to the more interesting of his points.

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References

  1. K. Marvel, G.A. Schmidt, R.L. Miller, and L.S. Nazarenko, "Implications for climate sensitivity from the response to individual forcings", Nature Climate Change, vol. 6, pp. 386-389, 2015. http://dx.doi.org/10.1038/nclimate2888

Anti-scientists

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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References

  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, 2015. http://dx.doi.org/10.1007/s00704-015-1597-5

New On-line Classes and Models

Filed under: — david @ 6 February 2016

My free online class on Coursera.org entitled Global Warming I: The Science and Modeling of Climate Change has already served 45,000 people (started, not finished) in the four times that it’s run. Now it’s set up in a new format, called “on demand mode”, which allows people to start, progress, and finish on their own calendars. This would be an advantage if a teacher wanted to use the material to supplement a class; a new cohort of learners is launched every month, so the next class start date is never more than a month away.

A new, supplemental class to the first one has been added and will come online on Monday, called Global Warming II: Create Your Own Models in Python or Fortran. This takes advantage of new code-grading machinery at Coursera to automatically run your code through its paces. There is also a peer code-review step, where you will get feedback on your commenting and variable-naming skills, and provide feedback to others. The class gives detailed instructions to create simple models of: time evolution of global temperature, the ice albedo feedback drop into snowball Earth, an ice sheet, and a shallow-water circulation model. The class is intended for people who are new to programming, or new to Python, or wish to enhance their understanding and appreciation of some cool science of Earth’s climate system.

The classes are supported by the same interactive on-line interactive climate system models as before, at http://climatemodels.uchicago.edu/, with some new additions, both of which generate animations of their time-dependent solutions.

One is a Hurricane simulator using a model from Kerry Emanuel, which can demonstrate the sensitivity of ocean temperature, ocean mixing, and atmospheric structure on hurricane evolution.

The other, the Permafrost model, is a simulation of a soil or sediment column in which ice and methane hydrate can form. The model shows how the brine salinity thermodynamically excludes methane hydrate from forming until you get to the base of the permafrost zone, and also how long it takes to warm a soil column by warming the surface. This model shows why I do not believe in an imminent methane climate catastrophe from Arctic Ocean methane hydrates.


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