There is an interesting news article ($) in Science this week by Paul Voosen on the increasing amount of transparency on climate model tuning. (Full disclosure, I spoke to him a couple of times for this article and I’m working on tuning description paper for the US climate modeling centers). The main points of the article are worth highlighting here, even if a few of the characterizations are slightly off.
Climate modelling
Q & A about the Gulf Stream System slowdown and the Atlantic ‘cold blob’
Last weekend, in Reykjavik the Arctic Circle Assembly was held, the large annual conference on all aspects of the Arctic. A topic of this year was: What’s going on in the North Atlantic? This referred to the conspicuous ‘cold blob’ in the subpolar Atlantic, on which there were lectures and a panel discussion (Reykjavik University had invited me to give one of the talks). Here I want to provide a brief overview of the issues discussed.
What is the ‘cold blob’?
This refers to exceptionally cold water in the subpolar Atlantic south of Greenland. In our paper last year we have shown it like this (see also our RealClimate post about it):
Fig. 1 Linear temperature trends from 1901 to 2013 according to NASA data. Source: Rahmstorf et al, Nature Climate Change 2015.
[Read more…] about Q & A about the Gulf Stream System slowdown and the Atlantic ‘cold blob’
The Snyder Sensitivity Situation
Nature published a great new reconstruction of global temperatures over the past 2 million years today. Snyder (2016) uses 61 temperature reconstructions from 59 globally diverse sediment cores and a correlation structure from model simulations of the last glacial maximum to estimate (with uncertainties) the history of global temperature back through the last few dozen ice ages cycles. There are multiple real things to discuss about this – the methodology, the relatively small number of cores being used (compared to what could have been analyzed), the age modeling etc. – and many interesting applications – constraints on polar amplification, the mid-Pleistocene transition, the duration and nature of previous interglacials – but unfortunately, the bulk of the attention will be paid to a specific (erroneous) claim about Earth System Sensitivity (ESS) that made it into the abstract and was the lead conclusion in the press release.
The paper claims that ESS is ~9ºC and that this implies that the long term committed warming from today’s CO2 levels is a further 3-7ºC. This is simply wrong.
[Read more…] about The Snyder Sensitivity Situation
References
- C.W. Snyder, "Evolution of global temperature over the past two million years", Nature, vol. 538, pp. 226-228, 2016. http://dx.doi.org/10.1038/nature19798
Do regional climate models add value compared to global models?
Global climate models (GCM) are designed to simulate earth’s climate over the entire planet, but they have a limitation when it comes to describing local details due to heavy computational demands. There is a nice TED talk by Gavin that explains how climate models work.
We need to apply downscaling to compute the local details. Downscaling may be done through empirical-statistical downscaling (ESD) or regional climate models (RCMs) with a much finer grid. Both take the crude (low-resolution) solution provided by the GCMs and include finer topographical details (boundary conditions) to calculate more detailed information. However, does more details translate to a better representation of the world?
The question of “added value” was an important topic at the International Conference on Regional Climate conference hosted by CORDEX of the World Climate Research Programme (WCRP). The take-home message was mixed on whether RCMs provide a better description of local climatic conditions than the coarser GCMs.
[Read more…] about Do regional climate models add value compared to global models?
Comparing models to the satellite datasets
How should one make graphics that appropriately compare models and observations? There are basically two key points (explored in more depth here) – comparisons should be ‘like with like’, and different sources of uncertainty should be clear, whether uncertainties are related to ‘weather’ and/or structural uncertainty in either the observations or the models. There are unfortunately many graphics going around that fail to do this properly, and some prominent ones are associated with satellite temperatures made by John Christy. This post explains exactly why these graphs are misleading and how more honest presentations of the comparison allow for more informed discussions of why and how these records are changing and differ from models.
[Read more…] about Comparing models to the satellite datasets
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. [Read more…] about Millennia of sea-level change
References
- 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
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
- 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
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
- 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…
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
- 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
- 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’
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
- 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
- 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