RealClimate logo

Live (almost) from AGU–Dispatch #6

Filed under: — raypierre @ 14 December 2007

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.
More »

Notes from The Gathering #5: Arctic sea ice: is it tipped yet?

Filed under: — david @ 13 December 2007

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. More »

Live (almost) from AGU–Dispatch #4

Filed under: — raypierre @ 13 December 2007

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.
More »

Tropical tropospheric trends

Filed under: — group @ 12 December 2007

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.
More »

Hot off the projector #3: Atmospheric CO2 to 800 kyr ago

Filed under: — david @ 12 December 2007

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 … More »