Tuesday, 8 October 2013

Global Warming Caused by Jupiter - thank heavens! (semi-empirically)

When I noticed a comment and link from Nicola Scafetta on Judith Curry's blog, my curiosity was piqued. Back in the day, Scafetta, Moon et al. were lauded as champions of the climate change doubters community and by and large critiqued negatively by most if not all of the climate scientists who blogged back then.

At the time, I'm fairly sure the furore was about attribution to Solar influences and, having kind of assumed that this had been looked at a lot recently and largely worked out, I thought I'd have a closer look.

The link kindly provided by Dr S. on JC's blog goes to a paywall, but the actual paper is available on his own page, here (for the time being). If the link goes down, no worry, I've saved a pdf just in case.

So what's it all about, NS? Snappily entitled Discussion on climate oscillations: CMIP5 general circulation models versus a semi-empirical harmonic model based on astronomical cycles, the paper compares a semi-empirical model produced by NS with the CMIP5 models and finds the latter wanting. Quoting:

     Power spectra of global surface temperature (GST) records (available since 1850)      reveal major periodicities at about 9.1, 10–11, 19–22 and 59–62 years. Equivalent  oscillations are found in numerous multisecular paleoclimatic records. The Coupled  Model Intercomparison Project 5 (CMIP5) general circulation models (GCMs), to be used  in the IPCC Fifth Assessment Report (AR5, 2013), are analyzed and found not able to  reconstruct this variability. In particular, from 2000 to 2013.5 a GST plateau is observed  while the GCMs predicted a warming rate of about 2 °C/century. In contrast, the  hypothesis that the climate is regulated by specific natural oscillations more  accurately fits the GST records at multiple time scales.

As usual, the reading is my non-scientist's rough watering down. In summary, about half of the GW observed since 1850 'could' be attributed to 'natural oscillations'. These oscillations are linked to half a dozen interplanetary relations - Sun/Moon, Sun/Jupiter, Jupiter/Saturn, etc.

Now this hypothesis, that our temperature is affected significantly by such distant forces as those from Jupiter and Saturn, is not an new revelation from Scafetta, so perhaps I'm behind the curve on this one again, but to my (untrained) eye, this hypothesis seems at the least counter-intuitive. It puts me in mind (no doubt unfairly) of Astrology.

I've no doubt that a suitably qualified analyst can explain very simply whether this is a legitimate line of enquiry or not - I'll try not to let my prejudices get in the way - but since I'm fairly sure someone will trot this out as 'proof' or 'evidence' that AGW is not all it's cracked up to be, it would be useful to get clarity on what is wrong with this hypothesis. As usual, depending on responses...