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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

Two-year old turkey

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The blogosphere is abuzz with the appearance of a second tranche of the emails stolen from CRU just before thanksgiving in 2009. Our original commentary is still available of course (CRU Hack, CRU Hack: Context, etc.), and very little appears to be new in this batch. Indeed, even the out-of-context quotes aren’t that exciting, and are even less so in-context.

A couple of differences in this go around are worth noting: the hacker was much more careful to cover their tracks in the zip file they produced – all the file dates are artificially set to Jan 1 2011 for instance, and they didn’t bother to hack into the RealClimate server this time either. Hopefully they have left some trails that the police can trace a little more successfully than they’ve been able to thus far from the previous release.

But the timing of this release is strange. Presumably it is related to the upcoming Durban talks, but it really doesn’t look like there is anything worth derailing there at all. Indeed, this might even increase interest! A second release would have been far more effective a few weeks after the first – before the inquiries and while people still had genuine questions. Now, it just seems a little forced, and perhaps a symptom of the hacker’s frustration that nothing much has come of it all and that the media and conversation has moved on.

If anyone has any questions about anything they see that seems interesting, let us know in the comments and we’ll see if we can provide some context. We anticipate normal service will be resumed shortly.

The IPCC report on extreme climate and weather events

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The IPCC recently released the policy-maker’s summary (SREX-SPM) on extreme weather and climate events. The background for this report is a larger report that is due to be published in the near future, and one gets a taste of this in the ‘wordle‘ figure below. By the way, the phrase ‘ET’ in this context does not refer ‘extra-terrestrial’, and ‘AL’ is not a person, but these refer to the way of citing many scholars: ‘et al.‘

Fig. 1. The text analysis according to http://www.wordle.net/

[Read more…] about The IPCC report on extreme climate and weather events

Scientific confusion

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“We have not succeeded in answering all our problems. The answers we have found only serve to raise a whole set of new questions. In some ways we feel we are as confused as ever, but we believe we are confused on a higher level and about more important things.”


I read this quote on a wall on Mark Cane’s office at LDEO (Columbia) many years ago and always wondered where it came from. He found it as an epigram in a book on ‘Stochastic Differential Equations‘ by Bernt Øksendal where it is sourced to a sign outside the mathematics reading room at Tromsø University. The actual source appears to be a 1951 report on an education workshop by Earl C. Kelley, a professor at Wayne University (sleuthing by QI).

Times Atlas map of Greenland to be corrected

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We were pleased to hear from the University of Arizona’s Jeff Kargel that the Times Atlas folks are now updating their atlas of Greenland. As we reported earlier, the first edition was completely in error, and led to some rather bizarre claims about the amount of ice loss in Greenland. Kargel reports that HarperCollins (publisher of the Times Atlas) has now fully retracted their error and has produced a new map of Greenland that will be made available as a large-format, 2-side map insert for the Atlas and will also be available free online. Meanwhile, Kargel and colleagues have produced their own updated small-scale map and have written a paper that includes both their new map and a description of the incident that led up to it. Kargel was instrumental in pushing the cryosphere community to send a strong message to the publishers that they needed to correct their mistake. (A pre-print of the paper, currently under review and under public discussion on Cryolist, is available here.)

Figure 1 in Kargel et al. (2011) generated by a collaboration of the Geological Survey of Denmark and Greenland (GEUS) and the Programme for Monitoring of the Greenland Ice Sheet (PROMICE) with the Polar Geospatial Center Department of Geology and Geophysics, University of Minnesota. Contact: Michele Citterio (GEUS) for questions about the glacier outlines or Paul Morin (UMinn.) for questions about the MODIS base image mosaic.

HarperCollins is to be commended for listening to the scientific community and producing a corrected map. Unfortunately, and despite recent events demonstrating that popular allegations against climate scientists are all wrong, HarperCollins still says on their web site that it’s all the scientists’ fault for not being clear (“The one thing that is very apparent is that there is no clarity in the scientific and cartographic community on this issue”,they write). Hmm. Our own view is that anyone flying over Greenland en route to Europe from North America would instantly have recognized a problem with the Times Atlas (assuming they knew their location of course). As Kargel and colleagues write in their paper:

“Distinguishing manifest, ignorable nonsense from falsehoods that might take root in the public mind is difficult, but the magnitude of and apparent authority behind this particular mistake seemed to warrant a rapid and firm response. The eventually constructive reaction of HarperCollins, which not only withdrew its mistaken claim but also produced a new map to be included in the Times Atlas as an insert, shows the value of such a response. No less than grotesque trivialization, grotesque exaggeration of the pace or consequences of climate change needs to be countered energetically.”

Nevertheless, they caution that “scientists cannot possibly challenge all of the innumerable misunderstandings and misrepresentations of their work in public discourse.”

Well said. Of course, many scientists can do more, and we encourage all of our colleagues to speak publically about their research and, as the international glaciological research community did in this case, to try to correct misconceptions. At the same time, hopefully, HarperCollins will catch on and recognize that being scientifically literate is not just scientists’ responsibility, but is everyone’s responsibility.

On record-breaking extremes

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It is a good tradition in science to gain insights and build intuition with the help of thought-experiments. Let’s perform a couple of thought-experiments that shed light on some basic properties of the statistics of record-breaking events, like unprecedented heat waves. I promise it won’t be complicated, but I can’t promise you won’t be surprised.
[Read more…] about On record-breaking extremes