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Millennia of sea-level change

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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. [Read more…] about Millennia of sea-level change

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, 2016. http://dx.doi.org/10.1073/pnas.1517056113

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

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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.

[Read more…] about Marvel et al (2015) Part III: Response to Nic Lewis

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

Marvel et al (2015) Part 1: Reconciling estimates of climate sensitivity

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This post is related to the substantive results of the new Marvel et al (2015) study. There is a separate post on the media/blog response.

The recent paper by Kate Marvel and others (including me) in Nature Climate Change looks at the different forcings and their climate responses over the historical period in more detail than any previous modeling study. The point of the paper was to apply those results to improve calculations of climate sensitivity from the historical record and see if they can be reconciled with other estimates. But there are some broader issues as well – how scientific anomalies are dealt with and how simulation can be used to improve inferences about the real world. It also shines a spotlight on a particular feature of the IPCC process…

[Read more…] about Marvel et al (2015) Part 1: Reconciling estimates of climate sensitivity

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

And the winner is…

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Remember the forecast of a temporary global cooling which made headlines around the world in 2008? We didn’t think it was reliable and offered a bet. The forecast period is now over: we were right, the forecast was not skillful.

Back around 2007/8, two high-profile papers claimed to produce, for the first time, skilful predictions of decadal climate change, based on new techniques of ocean state initialization in climate models. Both papers made forecasts of the future evolution of global mean and regional temperatures. The first paper, Smith et al. (2007), predicted “that internal variability will partially offset the anthropogenic global warming signal for the next few years. However, climate will continue to warm, with at least half of the years after 2009 predicted to exceed the warmest year currently on record.” The second, Keenlyside et al., (2008), forecast in contrast that “global surface temperature may not increase over the next decade, as natural climate variations in the North Atlantic and tropical Pacific temporarily offset the projected anthropogenic warming.”

This month marks the end of the forecast period for Keenlyside et al and so their forecasts can now be cleanly compared to what actually happened. This is particularly interesting to RealClimate, since we offered a bet to the authors on whether the results would be accurate based on our assessment of their methodology. They ignored our offer but now the time period of the bet has passed, it’s worth checking how it would have gone.

[Read more…] about And the winner is…

References

  1. D.M. Smith, S. Cusack, A.W. Colman, C.K. Folland, G.R. Harris, and J.M. Murphy, "Improved Surface Temperature Prediction for the Coming Decade from a Global Climate Model", Science, vol. 317, pp. 796-799, 2007. http://dx.doi.org/10.1126/science.1139540
  2. N.S. Keenlyside, M. Latif, J. Jungclaus, L. Kornblueh, and E. Roeckner, "Advancing decadal-scale climate prediction in the North Atlantic sector", Nature, vol. 453, pp. 84-88, 2008. http://dx.doi.org/10.1038/nature06921

NOAA temperature record updates and the ‘hiatus’

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In a new paper in Science Express, Karl et al. describe the impacts of two significant updates to the NOAA NCEI (née NCDC) global temperature series. The two updates are: 1) the adoption of ERSST v4 for the ocean temperatures (incorporating a number of corrections for biases for different methods), and 2) the use of the larger International Surface Temperature Initiative (ISTI) weather station database, instead of GHCN. This kind of update happens all the time as datasets expand through data-recovery efforts and increasing digitization, and as biases in the raw measurements are better understood. However, this update is going to be bigger news than normal because of the claim that the ‘hiatus’ is no more. To understand why this is perhaps less dramatic than it might seem, it’s worth stepping back to see a little context…

[Read more…] about NOAA temperature record updates and the ‘hiatus’

References

  1. T.R. Karl, A. Arguez, B. Huang, J.H. Lawrimore, J.R. McMahon, M.J. Menne, T.C. Peterson, R.S. Vose, and H. Zhang, "Possible artifacts of data biases in the recent global surface warming hiatus", Science, vol. 348, pp. 1469-1472, 2015. http://dx.doi.org/10.1126/science.aaa5632
  2. B. Huang, V.F. Banzon, E. Freeman, J. Lawrimore, W. Liu, T.C. Peterson, T.M. Smith, P.W. Thorne, S.D. Woodruff, and H. Zhang, "Extended Reconstructed Sea Surface Temperature Version 4 (ERSST.v4). Part I: Upgrades and Intercomparisons", Journal of Climate, vol. 28, pp. 911-930, 2015. http://dx.doi.org/10.1175/JCLI-D-14-00006.1

Global warming and unforced variability: Clarifications on recent Duke study

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Guest Commentary from Patrick Brown and Wenhong Li, Duke University

We recently published a study in Scientific Reports titled Comparing the model-simulated global warming signal to observations using empirical estimates of unforced noise. Our study seemed to generated a lot of interest and we have received many inquires regarding its findings. We were pleased with some of coverage of our study (e.g., here) but we were disappointed that some outlets published particularly misleading articles (e.g, here, here, and here). Since there appears to be some confusion regarding our study’s findings, we would like to clarify some points (see also MM4A’s discussion).

[Read more…] about Global warming and unforced variability: Clarifications on recent Duke study

References

  1. P.T. Brown, W. Li, E.C. Cordero, and S.A. Mauget, "Comparing the model-simulated global warming signal to observations using empirical estimates of unforced noise", Scientific Reports, vol. 5, 2015. http://dx.doi.org/10.1038/srep09957

The return of the iris effect?

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Guest commentary from Andy Dessler (TAMU)

When a new scientific hypothesis is published, two questions always occur to me:

  1. Did the authors convincingly show the hypothesis was correct?
  2. If not, is the hypothesis actually correct?

The answers to these two questions may not be the same. A good example is Wegener’s theory of continental drift — his idea was fundamentally correct, but he lacked the data and physical mechanisms to convince the rest of scientific community. It would take several decades before enough data were gathered that the scientific community wholeheartedly endorsed plate tectonics.

In 2001, Prof. Richard Lindzen and colleagues published his “iris hypothesis” (Lindzen et al., 2001). The hypothesis has two parts: First, in a warmer climate, enhanced precipitation efficiency will lead to less cloud being detrained into the troposphere from convection. Second, with less cloud cover, more infrared radiation can escape to space, thereby creating a strong climate-stabilizing negative cloud feedback that prevents significant warming from increasing greenhouse gases.

Within a few years, a number of analyses made clear that the evidence provided by Lindzen et al. had problems [e.g., Hartmann and Michelsen, 2002; Lin et al., 2002; Lin et al., 2004; Su et al., 2008]. Lindzen and colleagues responded to these critiques, but few were convinced by their arguments. By 2006, when I submitted an analysis of tropospheric water vapor that investigated whether there was an iris in that, one of the reviewers pointedly questioned why anyone was still working on this issue. I subsequently withdrew the paper.

Nevertheless, just because Lindzen et al. did not convincingly demonstrate their case does not mean the iris hypothesis is wrong. With that idea in mind, a new paper by Mauritsen and Stevens (2015) revisits the iris hypothesis. The most important part of their work was to simulate the iris in a climate model by artificially tweaking the model’s convective parameterization. They do this by increasing the rate of conversion of cloud water to rain as the climate warms, thereby reducing the amount of detraining condensate in a warmer climate. In effect, this imposes a tweak that mimics the iris effect – it is not a demonstration that the iris effect emerges from any physical mechanisms.

What they find is that, even though cloud cover is reduced as the climate warms, it does not generate a strong negative cloud feedback. While reducing cloud cover does indeed let more infrared energy out, it also lets more sunlight in. These two effects, while independently large, act in opposite directions. The net effect is the small residual of their difference. For runs with the strongest “iris”, the model’s climate sensitivity is reduced from 2.8°C for doubled carbon dioxide to 2.2°C — still well within the IPCC’s canonical range.

It’s also worth pointing out what this study doesn’t prove. It doesn’t validate Lindzen et al.’s original hypothesis — in fact, it does the opposite – even with an iris effect, the sensitivity does not become negligible. Additionally, there is little evidence that the rate of conversion of cloud water to rain actually changes with temperature, although Mauritsen and Stevens show that incorporating the iris into the model does improve the model’s simulations of some aspects of the climate system (even though it doesn’t change climate sensitivity much).

I view this as a what-if calculation of the impact of such a process. Future research may validate this, or it may not. This kind of calculation is one of the reasons why we like using models, of course.

Another argument against the iris comes from my work looking at the cloud feedback in response to short-term climate variability. If the iris provided a strong negative feedback, then we would expect to see it in response to short-term climate fluctuations. Analysis of observations doesn’t show anything like that (Dessler, 2013).

Overall, I think the debate over the iris hypothesis is a testament to the efforts the scientific community goes through to evaluate challenges to theories and find ways to improve our understanding of the climate (for instance, see Bill Ruddiman’s post from last week). This is one of the most important reasons I have such high confidence in the scientific process for figuring out how the universe works.

References

  1. R.S. Lindzen, M. Chou, and A.Y. Hou, "Does the Earth Have an Adaptive Infrared Iris?", Bulletin of the American Meteorological Society, vol. 82, pp. 417-432, 2001. http://dx.doi.org/10.1175/1520-0477(2001)082<0417:DTEHAA>2.3.CO;2
  2. D.L. Hartmann, and M.L. Michelsen, "No Evidence for Iris", Bulletin of the American Meteorological Society, vol. 83, pp. 249-254, 2002. http://dx.doi.org/10.1175/1520-0477(2002)083<0249:NEFI>2.3.CO;2
  3. B. Lin, B.A. Wielicki, L.H. Chambers, Y. Hu, and K. Xu, "The Iris Hypothesis: A Negative or Positive Cloud Feedback?", Journal of Climate, vol. 15, pp. 3-7, 2002. http://dx.doi.org/10.1175/1520-0442(2002)015<0003:TIHANO>2.0.CO;2
  4. B. Lin, T. Wong, B.A. Wielicki, and Y. Hu, "Examination of the Decadal Tropical MeanERBSNonscanner Radiation Data for the Iris Hypothesis", Journal of Climate, vol. 17, pp. 1239-1246, 2004. http://dx.doi.org/10.1175/1520-0442(2004)017<1239:EOTDTM>2.0.CO;2
  5. H. Su, J.H. Jiang, Y. Gu, J.D. Neelin, B.H. Kahn, D. Feldman, Y.L. Yung, J.W. Waters, N.J. Livesey, M.L. Santee, and W.G. Read, "Variations of tropical upper tropospheric clouds with sea surface temperature and implications for radiative effects", Journal of Geophysical Research: Atmospheres, vol. 113, 2008. http://dx.doi.org/10.1029/2007JD009624
  6. T. Mauritsen, and B. Stevens, "Missing iris effect as a possible cause of muted hydrological change and high climate sensitivity in models", Nature Geoscience, vol. 8, pp. 346-351, 2015. http://dx.doi.org/10.1038/ngeo2414
  7. A.E. Dessler, "Observations of Climate Feedbacks over 2000–10 and Comparisons to Climate Models*", Journal of Climate, vol. 26, pp. 333-342, 2013. http://dx.doi.org/10.1175/jcli-d-11-00640.1

Reflections on Ringberg

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As previewed last weekend, I spent most of last week at a workshop on Climate Sensitivity hosted by the Max Planck Institute at Schloss Ringberg. It was undoubtedly one of the better workshops I’ve attended – it was focussed, deep and with much new information to digest (some feel for the discussion can be seen from the #ringberg15 tweets). I’ll give a brief overview of my impressions below.

[Read more…] about Reflections on Ringberg

Climate Sensitivity Week

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Some of you will be aware that there is a workshop on Climate Sensitivity this week at Schloss Ringberg in southern Germany. The topics to be covered include how sensitivity is defined (and whether it is even meaningful (Spoiler, yes it is)), what it means, how it can be constrained, what the different flavours signify etc. There is an impressive list of attendees with a very diverse range of views on just about everything, and so I am looking forward to very stimulating discussions.

[Read more…] about Climate Sensitivity Week

The Soon fallacy

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As many will have read, there were a number of press reports (NYT, Guardian, InsideClimate) about the non-disclosure of Willie Soon’s corporate funding (from Southern Company (an energy utility), Koch Industries, etc.) when publishing results in journals that require such disclosures. There are certainly some interesting questions to be asked (by the OIG!) about adherence to the Smithsonian’s ethics policies, and the propriety of Smithsonian managers accepting soft money with non-disclosure clauses attached.

However, a valid question is whether the science that arose from these funds is any good? It’s certainly conceivable that Soon’s work was too radical for standard federal research programs and that these energy companies were really taking a chance on blue-sky high risk research that might have the potential to shake things up. In such a case, someone might be tempted to overlook the ethical lapses and conflicts of interest for the sake of scientific advancement (though far too many similar post-hoc justifications have been used to excuse horrific unethical practices for this to be remotely defendable).

Unfortunately, the evidence from the emails and the work itself completely undermines that argument because the work and the motivation behind it are based on a scientific fallacy.
[Read more…] about The Soon fallacy