Today was the all-Union session on Tipping Points, and several people have asked for comments on what went on there. I suppose this session might have been useful for people who had to miss the more detailed discussion in specialized sections, but I don’t have much to say about most of the talks, since they for the most part went over issues like ice sheet dynamics and rapid arctic sea ice loss, which I’ve discussed in earlier dispatches. Myself, I never found the notion of “tipping points” to be a very useful contribution to public discourse. The concept is ill-defined and very prone to be misunderstood — as in: we’ve passed a tipping point so it’s too late to do anything (might as well have a party). In Hansen’s talk, he did try to clarify what he meant by a tipping point. His notion of this has less to do with what mathematicians understand as “bifurcations,” and more to do with a kind of inertia in the climate system. He means things like having passed a threshold of CO2 which, given warming in the pipeline and the lifetime of CO2, commits a certain discrete event — e.g. loss of perennial sea ice or the Amazon rainforest– to occurring even if we were to later reduce emissions to zero. He tried to distinguish between reversible and irreversible tipping points. The talk was good cheerleading, after a fashion, but rather thin on real examples of what might be a tipping point in his definition. Everything he said was true (especially the emphasis on the importance of a rapid phase-out of coal burning) but the talk had much more to do with energy policy and lamentation of the power of entrenched fossil fuel interests than it had to do with climate science.
[Read more…] about Live (almost) from AGU–Dispatch #6
Climate Science
Notes from The Gathering #5: Arctic sea ice: is it tipped yet?
The summer of 2007 was apocalyptic for Arctic sea ice. The coverage and thickness of sea ice in the Arctic has been declining steadily over the past few decades, but this year the ice lost an area about the size of Texas, reaching its minimum on about the 16th of September. Arctic sea ice seems to me the best and more imminent example of a tipping point in the climate system. A series of talks aimed to explain the reason for the meltdown. [Read more…] about Notes from The Gathering #5: Arctic sea ice: is it tipped yet?
Live (almost) from AGU–Dispatch #4
Ptarmigans are Back! Fans of the Sheep Albedo Feedback will remember these little fellows over on the right (photo credit: Ken Tape) from the immortal paper by Squeak and Diddlesworth on the influence of ptarmigan populations on the Laurentide Ice Sheet. 
In Session C33A on Wednesday, Ken Tape of the University of Alaska presented a paper on the influence of ptarmigan grazing on shrubbification of the Alaskan tundra. It seems that when there is deep snow cover, ptarmigan browsing is concentrated on those few willows that stick up above the snow. They eat the buds, which inhibits willow growth. These tall willows are the ones that have managed to benefit most by climate warming, but the ptarmigan provide a stabilizing feedback, up to a point. An interesting thing is the ptarmigan don’t like to perch. 98% of the winter buds within a half meter of the snow surface get eaten, but only 48% of the buds above that browse level. So, if the shrubs grow fast enough to get above the browse level, they can beat the ptarmigans. This seems to be happening more and more.
[Read more…] about Live (almost) from AGU–Dispatch #4
Tropical tropospheric trends
Once more unto the breach, dear friends, once more!
Some old-timers will remember a series of ‘bombshell’ papers back in 2004 which were going to “knock the stuffing out” of the consensus position on climate change science (see here for example). Needless to say, nothing of the sort happened. The issue in two of those papers was whether satellite and radiosonde data were globally consistent with model simulations over the same time. Those papers claimed that they weren’t, but they did so based on a great deal of over-confidence in observational data accuracy (see here or here for how that turned out) and an insufficient appreciation of the statistics of trends over short time periods.
Well, the same authors (Douglass, Pearson and Singer, now joined by Christy) are back with a new (but necessarily more constrained) claim, but with the same over-confidence in observational accuracy and a similar lack of appreciation of short term statistics.
[Read more…] about Tropical tropospheric trends
Hot off the projector #3: Atmospheric CO2 to 800 kyr ago
Just a few minutes ago Chappellaz et al presented the deepest dregs of greenhouse gas concentration data from the EPICA ice core in Antarctica, extending the data back to 800,000 years ago. In Al Gore’s movie you saw what was at that time the longest record of atmospheric greenhouse gas concentrations, back to 650 kyr, and their astonishing correlation with Antarctic temperature. This iconic superstar record has probably consumed as many eyeball-hours as any in climate science, alongside other classics such as the Jones et al. global temperature trends, the Moana Loa recent CO2 record, and the hockey stick. The Antarctic CO2 record has spawned countless internet rants about the CO2 lag behind temperature, and the circle of cause and effect between CO2 and climate. And the new data say … [Read more…] about Hot off the projector #3: Atmospheric CO2 to 800 kyr ago
Live (almost) from AGU–Dispatch #2
Before I get started with a few hasty remarks on today’s events, let me remind you that Lonnie Thompson’s Frontiers in Geophysics lecture will be webcast live on Wednesday at 1815 Pacific time. A link to the webcast can be found here. The lecture is entitled “Abrupt Climate Change and Our Future”. At the same page you’ll find links to Arvidson’s Whipple lecture on Mars exploration, which will be webcast at 14:20. Enjoy! Wish you were here.
Now, let me say at once how inspiring it is to see so much first-rate innovative science arrayed here. There are a lot of geophysicists in the world, and most of them are very, very good. It is especially encouraging to see so much new, young talent in all areas. I spend all too much of my time on RealClimate writing about bad science, it is great to come here and get a reality check.
Live (almost) from AGU–Dispatch #1
Welcome, dear readers. For all of you who have eagerly been awaiting Part II of Les Chevaliers, thank you for your patience; with all the other interesting stuff coming up for discussion at RealClimate, the plans to post Part II ran up against the American Geophysical Union Fall Meeting, when 15,000 of our prime audience are holed up in San Francisco trying to decide which of a half dozen simultaneous sessions at any time best command their attention. Be of good cheer — Part II will be coming along in about another week. Meanwhile, Yours Truly offers a few off the cuff dispatches giving a personal and unedited view of a few things going on at AGU that may be of interest to the RealClimate readership.Myself, I have been spending a lot of time looking at some of the exciting new data coming in from planetary missions, but I’ll spare you that, and talk about things related to global change. I do not pretend that these are necessarily the most important things going on at the meeting, but they are a few things that I happen to have attended, and which caught my attention.
¿Están las tendencias de la temperatura del aire afectadas por la actividad económica?
) Para leer en español.
Past reconstructions: problems, pitfalls and progress
Many people hold the mistaken belief that reconstructions of past climate are the sole evidence for current and future climate change. They are not. However, they are very interesting and useful for all sorts of reasons: for modellers to test out theories of climate change, for geographers, archaeologists and historians to examine the impact of climate on past civilizations and ecosystems, and for everyone to get a sense of what climate is capable of doing, how fast it does it and why.
As a small part of that enterprise, the climate of the medieval period has received a very high (and sometimes disproportionate) profile in the public discourse – due in no small part to the mistaken notion that it is an important factor for the attribution of current climate change. Its existence as a period of generally warmer temperatures (at least in the Northern hemisphere) than the centuries that followed is generally accepted. But the timing, magnitude and spatial extent are much more uncertain. All previous multiproxy reconstructions indicate a Northern Hemisphere mean temperature less than current levels, though possibly on a par with the mid- 20th century. But there are only a few tenths of a degree in it, and so the description that it is likely to have been warmer now (rather than virtually certain) is used to express the level of uncertainty.
A confounding factor in discussions of this period is the unfortunate tendency of some authors to label any warm peak prior to the 15th Century as the ‘Medieval Warm Period’ in their record. This leads to vastly different periods being similarly labelled, often giving a misleading impression of coherence. For instance, in a recent paper it was defined as 1200-1425 CE well outside the ‘standard’ definition of 800-1200 CE espoused by Lamb.
Since a new ‘reconstruction’ of the last 2000 years from Craig Loehle is currently doing the rounds, we thought it might be timely to set out what the actual issues are in making such reconstructions (as opposed to the ones that are more often discussed), and how progress is being made despite the pitfalls.
[Read more…] about Past reconstructions: problems, pitfalls and progress
Goodbye to all that
This post announces my (William Connolley’s) departure from RealClimate, and indeed from the professional climate field in general, in favour of the wide world of Cambridge software engineering. I’ve enjoyed my time with (Real)Climate, but now its time to move on.