Saturday, April 7, 2012

Ratcheting Up the Rhetoric: IPCC time again

UPDATE April 8: Eschenbach has a devastating addition to his work: A fuller sample of CO2 proxies shows that CO2 kept going up over the last few thousand years, but temperature didn't. Once again there is no apparent connection between the two, a direct contradiction of Shakun et al's thesis--and it seems highly likely that Shakun et al new of this evidence, or should have known. The so-called 5th Annual Report of the Intergovernmental Panel on Climate Change (IPCC) is not expected for some time (Working Group I, "The Physical Science Basis," will issue the Summary for Policy Makers in about a year), but there is already a crescendo of news releases to support the global warming dogma. 1. Shakun et al, "Global warming preceded by increasing carbon dioxide concentrations ...," in Nature (2102). As Anthony Watts suggests, this is an indication of some evidence that the global warming movement desperately needs: a time when first CO2 went up, then temperature, and a plausible cause and effect can be traced. Al Gore's famous graphic, based on ice cores in one region, with both CO2 and temp spiking repeatedly at about the same time, actually shows in every case temperature up first, then CO2. This new paper considers more evidence, from more regions, and suggests that in the case of the end of the last Ice Age--a very significant temperature-related event--CO2 went up first, then temperature. Of course ice cores are a proxy for temperature, not a thermometer, and before 1850 there is usually no choice but to use proxies, and then defend why they are or may be reliable. Willis Eschenbach has looked at the actual proxies used in the study.
The main curiosity about these, other than the wide variety of amounts of warming, is the different timing of the warming. In some proxies it starts in 25,000 BC, in others it starts in 15,000 BC. Sometimes the warming peaks as early as 14,000 BC, and sometimes around 5,000 BC or later. Sometimes the warming continues right up to the present.
Since there is so much variation in the warming trends, plural, there is no way to co-relate any global warming trend with global CO2. 2. Booth et al, "Aerosols implicated as a prime driver of twentieth-century North Atlantic climate variability," Nature (2012). Amato Evans:
In a paper published on Nature’s website today, Booth et al. report their use of a state-of-the-art model of Earth’s climate to demonstrate that, at least over the past century, the AMO [Atlantic multidecadal oscillation] is largely the response of the upper ocean to changes in the concentration of pollution aerosols in the atmosphere. If correct, their results imply that the influence of human activity on the Atlantic regional climate is more pervasive than previously thought.
Judy Curry:
The result of this paper is driven by the so-called aerosol indirect effect, whereby the aerosols change the physical and optical properties of clouds. The uncertainty in the aerosol indirect effect is estimated in the AR4 to be by far the most uncertain element of radiative forcing, and the estimates in AR4 neglect many of the modes of the aerosol indirect effect, notably those associated with ice clouds.
Realistic error bars on current aerosol optical depth measurements are quite large; historical error bars must be huge. The fortuitous agreement of the aerosol optical depth with temperature variability is serendipitous climate magic, almost certainly with circular reasoning buried deeply or not so deeply in the aerosol estimates.
And finally, if this paper is correct and there is no AMO other than aerosol forcing, this is going to overthrow a very substantial body of work by oceanographers on the Atlantic Meridional Overturning Circulation . At best, the period in this paper covers 2 oscillations.
Color me unconvinced by this paper. I suspect that if this paper had been submitted to J. Geophysical Research or J. Climate, it would have been rejected. In any event, a much more lengthy manuscript would have been submitted with more details, allowing people to more critically assess this. By publishing this, Nature seems to be looking for headlines, rather than promoting good science.
A final reflection: recall my previous post on Trends, change points and hypotheses. This paper is squarely in the camp of hypothesis #1, where all climate variability (other than ENSO) is externally forced. I think this view is incorrect, but it seems to be ruling the IPCC’s mode of thinking.
3. Last for today: James Hansen, Al Gore's climate Rasputin. Acting on global warming is a moral cause like abolishing slavery. For the analogy to work, there has to be something analogous to slaves, along with a realistic plan to free them. Otherwise you're just struggling to find new names to apply to people who disagree with you.

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