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AGU Days 3&4

Filed under: — group @ 9 December 2011

(Day 1)(Day 2)

Sorry for the slow blogging, but with the AGU fun run starting at 6.15am, and the Awards ending at around ~10pm, and the actual science portion of the day squeezed in the middle, little time was available on Wednesday for reporting. Thursday seemed equally busy. So today you get two days in one.

One session on Wednesday that was really quite good was the session on Earth System Sensitivity. We’ve discussed this before (notably in discussing Hansen’s Target CO2 paper). The main idea is that the sensitivity of the climate system to a radiative forcing is not going to be constrained to effect only the factors included in GCM in 1979. That is, other feedbacks come into play – vegetation, ice sheets, aerosols, CH4 etc. will all change as a function a warming (or cooling), which are not included in the standard climate sensitivity definition. Talks by Eelco Rohling, Dan Lunt, and Jim Hansen all made excellent points on how one should think about constraints on ESS from paleo-climate records. The periods considered were mainly the Pleistocene ice age cycles, the LGM and the Pliocene, but Paul Valdes provided some interesting modeling that also included the Oligocene, the Turonian, the Maastrichtian and Eocene, indicating the importance of the base continental configuration, ice sheet position, and ocean circulation for sensitivity. Vegetation feedbacks were invariably reported as an amplifying feedback – which is interesting because that encompasses both ‘fast’ and ‘slow’ feedbacks.

Wednesday night was the awards, and as we reported, one of us (Gavin) was presented with the inaugural prize for Climate Communication. He will be posting a specific piece on this honor in a couple of days.

Thursday, there was a keynote (video available here) from Ben Santer at the Stephen Schneider event who persuasively argued that in doing the science necessary to refute baseless claims made in the media and in front of Congress, actual progress can be made beyond simply demonstrating that the original claim was made up. Specifically, he addressed a claim made by Will Happer, a Princeton professor, that no models demonstrate decadal variability in trends (which was not the case), and explored in depth the signal to noise ratio in determining climate trends much more comprehensively than had been done previously.

In sessions, there were a lot of papers on new approaches to estimating the climate of the common era (since 0 AD) – many of them using Bayesian methods of one sort or another. Hugues Goosse gave an interesting talk on paleo-data assimilation. A poster session had some first results from the CMIP5 models – including some intriguing results from Ben Booth looking at the Hadley Centre simulations of the role of aerosols in forcing multi-decadal variability in the North Atlantic.

Many of the lectures earlier this week are now available on demand. We hear that the Charney lecture from Graeme Stephens was particularly good.

(Day 5 and wrap up)

AGU 2011: Day 2

Filed under: — group @ 7 December 2011

(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", Rev. Geophys., 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

Filed under: — group @ 6 December 2011

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.
More »

References

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

AGU 2011: Day 1

Filed under: — group @ 6 December 2011

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)

Unforced variations: Dec 2011

Filed under: — group @ 1 December 2011

Open thread for December…


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