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.