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Data presentation: A trend lesson

I just came across an interesting way to eliminate the impression of a global warming. A trick used to argue that the global warming had stopped, and the simple recipe is as follows:

  • Cut off parts of the measurements and only keep the last 17 years.
  • Plot all the months of these 17 years to get plenty of data points.
  • A good idea is to show a streched plot with longer time axis.
  • More »

    Copernicus and Arrhenius: Physics Then and Physics Today

    Filed under: — eric @ 21 December 2011

    There was a really interesting article in Physics Today this past October on the parallels between the slow acceptance of the idea of anthropogenic climate change and of the idea that the earth circles the sun.
    More »

    Curve-fitting and natural cycles: The best part


    It is not every day that I come across a scientific publication that so totally goes against my perception of what science is all about. Humlum et al., 2011 present a study in the journal Global and Planetary Change, claiming that most of the temperature changes that we have seen so far are due to natural cycles.

    They claim to present a new technique to identify the character of natural climate variations, and from this, to produce a testable forecast of future climate. They project that

    the observed late 20th century warming in Svalbard is not going to continue for the next 20–25 years. Instead the period of warming may be followed by variable, but generally not higher temperatures for at least the next 20–25 years.

    However, their claims of novelty are overblown, and their projection is demonstrably unsound.

    More »

    References

    1. O. Humlum, J. Solheim, and K. Stordahl, "Identifying natural contributions to late Holocene climate change", Global and Planetary Change, vol. 79, pp. 145-156, 2011. http://dx.doi.org/10.1016/j.gloplacha.2011.09.005

    AGU 2011: Day 5 and wrap-up

    Filed under: — group @ 11 December 2011

    (Day 1)(Day 2)(Days 3&4)

    After 5 days, there is a definite slowdown in energy, desire to ask questions and attendance. But there were still a lot of good talks to be seen. Perhaps most relevant here were a few sessions talking about initial results from the CMIP5 models and the data with which they are being assessed. Overall, most comparisons to the CMIP3 models showed that despite substantial improvements in resolution, completeness, and scope, the CMIP5 models do not show any dramatic differences at the broad-scale diagnostics (global means etc.).

    This is not particularly surprising, since it is expected that the importance of the new simulations will be seen in the differences between model types (i.e. including carbon cycles, atmospheric chemistry etc.), or in new kinds of diagnostics from say, the initialized decadal predictions, that weren’t available before.

    Looking back at the whole meeting (20,000+ scientists, dozens of simultaneous sessions), it is perhaps worth noting the reasons why such meetings are so important. Obviously, no-one can see everything that is relevant to their research, or talk to everyone they might want to, but there is a lot that can be seen and absorbed much more efficiently than would be possible at home. The social aspect of conferences is also important – beer is an essential lubricant for geophysicists it seems. More important than the sessions are often the chance encounters on the escalators or corridors. Many people get to meet in person who only ever emailed – and this includes other bloggers as well as scientists. We met Eli Rabett, John Cook (Skeptical Science), Zeke Hausfather, Kate @ ClimateSight, Steve Easterbrook, and many others who are only known by their screen names and comments. Many of the scientists whose work has been discussed here recently were also present – Andreas Schmittner, Robert Rohde (of BEST), Jim Hansen, Ben Santer, Roy Spencer, along with many, many first timers whose work will become more prominent. The palpable sense of excitement at the directions the science is taking is very much driven by the bright ideas and new approaches being generated by the younger scientists – including undergraduates and graduate students. And it is the serendipitous encounters with these new voices that are the most unanticipated (and unplanned) benefits of these meetings. This doesn’t happen with Skype unfortunately.

    We know that we didn’t see everything we wanted to, so if any other attendees are reading this, we encourage them to point out in the comments any particular highpoints they came across – especially if the talks were part of those broadcast, or if the poster is available on-line.

    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

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