April 11, 2012

Atmospheric Aerosols and the Death of Nature

Filed under: Climate Changes, Gulf Stream

Big news last week was that new findings published in Nature magazine showed that human emissions of aerosols (primarily from fossil fuel use) have been largely responsible for the multi-decadal patterns of sea surface temperature variability in the Atlantic ocean that have been observed over the past 150 years or so. This variability—commonly referred to as the Atlantic Multidecadal Oscillation, or AMO—has been linked to several socially significant climate phenomena including the ebb and flow of active Atlantic hurricane periods and drought in the African Sahel.

This paper marks, in my opinion, the death of credibility for Nature on global warming. The first symptoms showed up in 1996 when they published a paper by Ben Santer and 13 coauthors that was so obviously cherry-picked that it took me and my colleagues about three hours to completely destroy it. Things have gone steadily downhill, from a crazy screamer by Jonathan Patz on mortality from warming that didn’t even bother to examine whether fossil fuels were associated with extended lifespan (they are), to the recent Shakun debacle. But the latest whopper, by Ben Booth and his colleagues at the UK Met Office indeed signals the death of Nature in this field.

The U.K. Met Office issued a press release touting the findings by several of their researchers, and didn’t pull any punches as to the study’s significance. The headline read “Industrial pollution linked to ‘natural’ disasters” and included things like:

These shifts in ocean temperature, known as the Atlantic Multidecadal Oscillation or AMO, are believed to affect rainfall patterns in Africa, South America and India, as well as hurricane activity in the North Atlantic - in extreme cases leading to humanitarian disasters.

Ben Booth, a Met Office climate processes scientist and lead author of the research, said: “Until now, no-one has been able to demonstrate a physical link to what is causing these observed Atlantic Ocean fluctuations, so it was assumed they must be caused by natural variability.

“Our research implies that far from being natural, these changes could have been largely driven by dirty pollution and volcanoes. If so, this means a number of natural disasters linked to these ocean fluctuations, such as persistent African drought during the 1970’s and 80’s, may not be so natural after all.”

An accompanying “News and Views” piece in Nature put the findings of Booth and colleagues in climatological perspective:

If Booth and colleagues’ results can be corroborated, then they suggest that multidecadal temperature fluctuations of the North Atlantic are dominated by human activity, with natural variability taking a secondary role. This has many implications. Foremost among them is that the AMO does not exist, in the sense that the temperature variations concerned are neither intrinsically oscillatory nor purely multidecadal.

But not everyone was so impressed with the conclusions of Booth et al.

For instance, Judith Curry had this to say at her blog, “Climate Etc.,”

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.

And Curry has good reason to be skeptical.

“In press” at the journal Geophysical Research Letters is a paper titled “Greenland ice core evidence for spatial and temporal variability of the Atlantic Multidecadal Oscillation” by Petr Chylek and colleagues, including Chris Folland of the Hadley Centre of the UK Met Office.

In this paper, Chylek et al. examine evidence of the AMO that is contained in several ice core records distributed across Greenland. The researchers were looking to see whether there were changes in the character of the AMO over different climatological periods in the past, such as the Little Ice Age and the Medieval Warm Period—periods that long preceded large-scale human aerosol emissions. And indeed they found some. The AMO during the Little Ice Age was characterized by a quasi-periodicity of about 20 years, while the during the Medieval Warm Period the AMO oscillated with a period of about 45 to 65 years.

And Chylek and colleagues had this to say about the mechanisms involved:

The observed intermittency of these modes over the last 4000 years supports the view that these are internal ocean-atmosphere modes, with little or no external forcing.

Better read that again. “…with little or no external forcing.”

Chylek’s conclusion is vastly different from the one reached by Booth et al., which in an Editorial, Nature touted as [emphasis added]:

[B]ecause the AMO has been implicated in global processes, such as the frequency of Atlantic hurricanes and drought in the Sahel region of Africa in the 1980s, the findings greatly extend the possible reach of human activity on global climate. Moreover, if correct, the study effectively does away with the AMO as it is currently posited, in that the multidecadal oscillation is neither truly oscillatory nor multidecadal.

Funny how the ice core records analyzed by Chylek (as opposed to the largely climate model exercise of Booth et al.) and show the AMO to be both oscillatory and multidecadal—and to be exhibiting such characteristics long before any possible human influence.

Judith Curry’s words “By publishing this, Nature seems to be looking for headlines, rather than promoting good science” seem to ring loud and true in light of further observation-based research.

May God rest the soul of Nature.

References:

Booth, B., et al., 2012. Aerosols implicated as a prime driver of twentieth-century North Atlantic climate variability. Nature, doi:10.1038/nature10946, http://www.nature.com/nature/journal/vaop/ncurrent/full/nature10946.html

Chylek, P., et al., 2012. Greenland ice core evidence for spatial and temporal variability of the Atlantic Multidecadal Oscillation. Geophysical Research Letters, in press, http://www.agu.org/pubs/crossref/pip/2012GL051241.shtml




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