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AGU 2011: Day 2

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(Day 1)

Tuesday


There were two interesting themes in the solar sessions this morning. The first was a really positive story about how instrumental differences between rival (and highly competitive) teams can get resolved. This refers to the calibration of measurements of the Total Solar Irradiance (TSI). As is relatively well known, the different satellite instruments over the last 30 or so years have shown a good coherence of variability – especially the solar cycle, but have differed markedly on the absolute value of the TSI (see the figure). In particular, four currently flying instruments (SORCE, ACRIM3, VIRGO and PREMOS) had offsets as large as 5W/m2. However, the development of a test-facility at NASA Langley the
University of Colorado, Laboratory for Atmospheric and Space Physics in Boulder
Colorado – an effort led by Greg Kopp’s group – has allowed people to test their instruments in a vacuum, with light levels comparable to the solar irradiance, and have the results compared to really high precision measurements. This was a tremendous technical challenge, but as Kopp stated, getting everyone on board was perhaps a larger social challenge.

The facility has enabled the different instrument teams to calibrate their instruments, and check for uncorrected errors, like excessive scattering and diffusive light contamination in the measurement chambers. In doing so, Richard Wilson of the ACRIM group reported that they found higher levels of scattering than they had anticipated, which was leading to slightly excessive readings. Combined with a full implementation of an annually varying temperature correction, their latest processed data product has reduced the discrepancy with the TIM instrument from over 5 W/m2 to less than 0.5 W/m2 – a huge improvement. The new PREMOS instrument onboard Picard, a french satellite, was also tested before launch last year, and they improved their calibration as well – and the data that they reported was also very close to the SORCE/TIM data: around 1361 W/m2 at solar minimum.

The errors uncovered and the uncertainties reduced as a function of this process was a great testament to the desire of everyone concerned to work towards finding the right answer – despite initial assumptions about who may have had the best design. The answer is that space borne instrumentation is hard to do, and thinking of everything that might go wrong is a real challenge.

The other theme was the discussion of the spectral irradiance changes – specifically by how much the UV changes over a solar cycle are larger in magnitude than the changes in the total irradiance. The SIM/SOLSTICE instruments on SORCE have reported much larger UV changes than previous estimates, and this has been widely questioned (see here for a previous discussion). The reason for the unease is that the UV instruments have a very large degradation of their signal over time, and the residual trends are quite sensitive to the large corrections that need to be made. Jerry Harder discussed those corrections and defended the SIM published data, while another speaker made clear how anomalous that data was. Meanwhile, some climate modellers are already using the SIM data to see whether that improves the model simulations of ozone and temperature responses in the stratosphere. However, the ‘observed’ data on this is itself somewhat uncertain – for instance, comparing the SAGE results (reported in Gray et al, 2011) with the SABER results (Merkel et al, 2011), shows a big difference in how large the ozone response is. So this remains a bit of a stumper.

The afternoon sessions on water isotopes in precipitation was quite exciting because of the number of people looking at innovative proxy archives, including cave records of 18O in calcite, or deuterium in leaf waxes, which are extending the coverage (in time and space) of this variable. Even more notable, was the number of these presentations that combined their data work with interpretations driven by GCM models that include isotope tracers that allow for more nuanced conclusions. This is an approach that was pioneered decades ago, but has taken a while to really get used routinely.

(Days 3&4)(Day 5 and wrap up)

References

  1. L.J. Gray, J. Beer, M. Geller, J.D. Haigh, M. Lockwood, K. Matthes, U. Cubasch, D. Fleitmann, G. Harrison, L. Hood, J. Luterbacher, G.A. Meehl, D. Shindell, B. van Geel, and W. White, "SOLAR INFLUENCES ON CLIMATE", Reviews of Geophysics, vol. 48, 2010. http://dx.doi.org/10.1029/2009RG000282
  2. A.W. Merkel, J.W. Harder, D.R. Marsh, A.K. Smith, J.M. Fontenla, and T.N. Woods, "The impact of solar spectral irradiance variability on middle atmospheric ozone", Geophysical Research Letters, vol. 38, pp. n/a-n/a, 2011. http://dx.doi.org/10.1029/2011GL047561

Global Temperature News

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There are two interesting pieces of news on the global temperature evolution.

First, today a paper by Grant Foster and Stefan Rahmstorf was published by Environmental Research Letters, providing a new analysis of the five available global (land+ocean) temperature time series. Foster and Rahmstorf tease out and remove the short-term variability due to ENSO, solar cycles and volcanic eruptions and find that after this adjustment all five time series match much more closely than before (see graph). That’s because the variability differs between the series, for example El Niño events show up about twice as strongly in the satellite data as compared to the surface temperatures. In all five adjusted series, 2009 and 2010 are the two warmest years on record. For details have a look over at Tamino’s Open Mind.
[Read more…] about Global Temperature News

References

  1. G. Foster, and S. Rahmstorf, "Global temperature evolution 1979–2010", Environmental Research Letters, vol. 6, pp. 044022, 2011. http://dx.doi.org/10.1088/1748-9326/6/4/044022

AGU 2011: Day 1

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A number of us are at the big AGU meeting in San Francisco this week (among 20,000 other geophysicists). We will try to provide a daily summary of interesting talks and posters we come across, but obviously this won’t be complete or comprehensive.

Other bloggers are covering the event (twitter #AGU11). A small number of the posters are viewable on their website as well.

Monday

Two good general talks this morning – Harry Elderfield gave the Emiliani lecture and started off with a fascinating discussion of the early discussions of Harold Urey and Cesare Emiliani on isotope thermometry – and showed that even Nobel Prize winners (Urey – for the discovery of deuterium) are sometimes quite wrong – in this case for insisting that the overall isotope ratio in the ocean could not ever change. (This talk should become available online here).

The second general talk was by author Simon Winchester who excellently demonstrated how to communicate about geology by using human stories. He gave a number of vignettes from his latest book about the Atlantic ocean – including stories of the shipwreck of the Dunedin Star on the ‘Skeleton coast’ of Southern Africa, time on St Helena, and the fate of his book on the Pacific that apparently only sold 12 copies… He finished with a mea culpa and gracious apology to the assorted geophysicists for his rather hurried comments on the Tohoku earthquake disaster that caused some consternation earlier this year. In his defense, he only had 90 minutes to write what he was unaware would be the Newsweek cover story that week.

In the science sessions in the afternoon, there was some good talks related to attributing extreme events including Marty Hoerling discussing the Moscow heat wave and a very different perspective from the cpdn group in Oxford. It would have been good to have had some actual discussion between the different people, but AGU is not conducive to much back and forth because of the very tight scheduling. The oxford group estimated (based on volunteer computing) that the likelihood of the Russian heat wave was something like 3 times more likely with 2000’s background climate vs the 1980’s. Some good points were made about the non-Gaussian nature of observed distributions the semantic challenges in explain attribution when there are both proximate and ultimate causes. Kerry Emanuel gave an update of his views on hurricane climate connections.

In the next door session, there was interesting discussion on the philosophy of climate modelling (from actual philosophers!) and the strategies that need to be adopted in dealing with the multi-model ensembles of CMIP3 and CMIP5.

(Day 2)(Days 3&4)(Day 5 and wrap up)

Ice age constraints on climate sensitivity

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There is a new paper on Science Express that examines the constraints on climate sensitivity from looking at the last glacial maximum (LGM), around 21,000 years ago (Schmittner et al, 2011) (SEA). The headline number (2.3ºC) is a little lower than IPCC’s “best estimate” of 3ºC global warming for a doubling of CO2, but within the likely range (2-4.5ºC) of the last IPCC report. However, there are reasons to think that the result may well be biased low, and stated with rather more confidence than is warranted given the limitations of the study.

[Read more…] about Ice age constraints on climate sensitivity

References

  1. A. Schmittner, N.M. Urban, J.D. Shakun, N.M. Mahowald, P.U. Clark, P.J. Bartlein, A.C. Mix, and A. Rosell-Melé, "Climate Sensitivity Estimated from Temperature Reconstructions of the Last Glacial Maximum", Science, vol. 334, pp. 1385-1388, 2011. http://dx.doi.org/10.1126/science.1203513

A Well Deserved Honor

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The rest of us here would like to congratulate Gavin on a well-deserved honor. He is the recipient of the inaugural AGU Climate Communication Prize. Since co-founding RealClimate back in 2004, Gavin has emerged as the de facto leader of RealClimate, having written the majority of our posts–and many of our best ones. One of his very first contributions “Michael Crichton’s State of Confusion” remains one of our most highly cited posts. One of his most recent, about what the recent CERN experiments do (and don’t) tell us about cloud processes, is a good example of his characteristic knack for explaining complex scientific issues with clarity and wit. Gavin also takes the lead role in dealing with the comments on RC posts. His almost non-stop, patient, response to the flood of comments that ensued in the week following the CRU email server hack in late 2009 impressed us all.

Gavin’s communication efforts, of course, go well beyond RealClimate. He is frequently quoted in mainstream news venues and often appears on radio and television news programs, to help communicate key aspects of climate science to the public. Here he is in an interview articulating both the science and the history of the science, and putting the recent politicizing of climate science into context. (It’s worth watching this interview to the end, by the way, for some thoughts on what you can do to improve communication of climate science.) He’s also produced a very accessible and beautiful book, Climate Change: Picturing the Science (with photographer Josh Wolfe).

Gavin’s efforts go well beyond the classic ‘public understanding of science’, since what he so successfully promotes is the ‘public understanding of research’. He makes it understandable and tangible how scientists work and think, not just what their results are. Gavin is a champion of easy access to data: see our Realclimate section on data sources. And, of course, a champion of making good use of the available data: see his many articles where he explains how particular questions (such as whether climate models agree with data) should not be speculated about but can be answered by anyone with basic skills simply by using publicly available data archives. Gavin’s work is often about empowering people to draw their own conclusions.

All of this is based on a solid foundation of his own scientific research: Gavin is a top-notch climatologist with an excellent publication record (h-index: 33), and we and our colleagues refer frequently to Gavin’s numerous papers in our own research and teaching. We only sometimes wonder whether his days have 30 hours, or how he finds the time to achieve all this.

Of course we’re a bit biased here at RealClimate, but it is truly hard to imagine a more deserving recipient for this award than Gavin.

Congratulations, once again, to our colleague and friend.

Mike Mann, Eric Steig, Stefan Rahmstorf, Jim Bouldin, Ray Pierrehumbert, David Archer, and the rest of RealClimate

Speculative polar cartography

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Guest commentary from Kevin Brown

The curious mismapping of Greenland’s ice sheet cover by the venerable Times Atlas recently has excited a lot of outraged commentary. But few people noted that this follows an old tradition of speculative cartography of the polar regions. ‘Modern’ mapmakers as early as the 16th century combined real facts and scientific knowledge with fundamental misinterpretations of that knowledge to create speculative mappings of the world’s unknown shores – and nowhere was this more prevalent than at the poles.

Early cartographers had a particularly difficult time mapping the Polar Regions. Factually, they based their maps on reports from mariners who dared sail the dangerous waters. This was supplemented by information from earlier maps, speculations based upon their personal theories of geography, religious beliefs, and the fiscal and political ambitions of their patrons.
[Read more…] about Speculative polar cartography

Cosmic rays and clouds: Potential mechanisms

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Guest Commentary by Jeffrey Pierce (Dalhousie U.)

I’ve written this post to help readers understand potential physical mechanisms behind cosmic-ray/cloud connections. But first I briefly want to explain my motivation.

Prior to the publication of the aerosol nucleation results from the CLOUD experiment at CERN in Nature several weeks ago Kirkby et al, 2011, I was asked by Nature Geoscience to write a “News and Views” on the CLOUD results for a general science audience. As an aerosol scientist, I found the results showing the detailed measurements of the influences of ammonia, organics and ions from galactic cosmic rays on aerosol formation exciting. While none of the results were entirely unexpected, the paper still represents a major step forward in our understanding of particle formation. This excitement is what I tried to convey to the general scientific audience in the News and Views piece. However, I only used a small portion of the editorial to discuss the implications to cosmic rays and clouds because (1) I felt that these implications represented only a small portion of the CLOUD findings, and (2) the CLOUD results address only one of several necessary conditions for cosmic rays to affect clouds, and have not yet tested the others.

Many of the news articles and blog posts covering the CLOUD article understandably focused much more on the cosmic-ray/cloud connection as it is easy to tie this connection into the climate debate. While many of the articles did a good job at reporting the CLOUD results within the big picture of cosmic-ray/cloud connections, some articles erroneously claimed that the CLOUD results proved the physics behind a strong cosmic-ray/cloud/climate connection, and others still just got it very muddled. A person hoping to learn more about cosmic rays and clouds likely ended up confused after reading the range of articles published. This potential confusion (along with many great questions and comments in Gavin’s CLOUD post) motivated me to write a general overview of the potential physical mechanisms for cosmic rays affecting clouds. In this post, I will focus on what we know and don’t know regarding the two major proposed physical mechanisms connecting cosmic rays to clouds and climate.
[Read more…] about Cosmic rays and clouds: Potential mechanisms

References

  1. J. Kirkby, J. Curtius, J. Almeida, E. Dunne, J. Duplissy, S. Ehrhart, A. Franchin, S. Gagné, L. Ickes, A. Kürten, A. Kupc, A. Metzger, F. Riccobono, L. Rondo, S. Schobesberger, G. Tsagkogeorgas, D. Wimmer, A. Amorim, F. Bianchi, M. Breitenlechner, A. David, J. Dommen, A. Downard, M. Ehn, R.C. Flagan, S. Haider, A. Hansel, D. Hauser, W. Jud, H. Junninen, F. Kreissl, A. Kvashin, A. Laaksonen, K. Lehtipalo, J. Lima, E.R. Lovejoy, V. Makhmutov, S. Mathot, J. Mikkilä, P. Minginette, S. Mogo, T. Nieminen, A. Onnela, P. Pereira, T. Petäjä, R. Schnitzhofer, J.H. Seinfeld, M. Sipilä, Y. Stozhkov, F. Stratmann, A. Tomé, J. Vanhanen, Y. Viisanen, A. Vrtala, P.E. Wagner, H. Walther, E. Weingartner, H. Wex, P.M. Winkler, K.S. Carslaw, D.R. Worsnop, U. Baltensperger, and M. Kulmala, "Role of sulphuric acid, ammonia and galactic cosmic rays in atmospheric aerosol nucleation", Nature, vol. 476, pp. 429-433, 2011. http://dx.doi.org/10.1038/nature10343

The unnoticed melt

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Guest commentary from Dirk Notz, MPI Hamburg

“Well, it’s not really good timing to write about global warming when the summer feels cold and rainy”, a journalist told me last week. Hence, at least here in Germany, there hasn’t been much reporting about the recent evolution of Arctic sea ice – despite the fact that Arctic sea ice extent in July, for example, was the lowest ever recorded for that month throughout the entire satellite record. Sea-ice extent in August was also extremely low, second only to August 2007 (Fig. 1). Whether or not we’re in for a new September record, the next weeks will show.



Figure 1: Evolution of Arctic sea-ice extent in July and August from 1979 until 2011. (NSIDC)

[Read more…] about The unnoticed melt