quinta-feira, 14 de novembro de 2013

Simple physics and climate

No doubt, our climate system is complex and messy. Still, we can sometimes make some inferences about it based on well-known physical principles. Indeed, the beauty of physics is that a complex systems can be reduced into simple terms that can be quantified, and the essential aspects understood.
A recent paper by Sloan and Wolfendale (2013) provides an example where they derive a simple conceptual model of how the greenhouse effect works from first principles. They show the story behind the expression saying that a doubling in CO2 should increase the forcing by a factor of log|2|. I have a fondness for such simple conceptual models (e.g. I’ve made my own attempt posted at arXiv) because they provide a general picture of the essence – of course their precision is limited by their simplicity.

However, the main issue discussed in the paper by Sloan and Wolfendale was not the greenhouse effect, but rather the question about galactic cosmic rays and climate. The discussion of the greenhouse effect was provided as a reference to the cosmic rays.
Even though we have discussed this question several times here at RC, Sloan and Wolfendale introduce some new information in connection with radiation, ionisation, and cloud formation. Even after having dug into all these other aspects, they do not find much evidence for the cosmic rays plying an important role. Their conclusions fit nicely with my own findings that also recently were published in the journal Environmental Research Letters.
The cosmic ray hypothesis is weakened further by observational evidence from satellites, as shown in another recent paper by Krissansen-Totton and Davies (2013) in Geophysical Research Letters, which also concludes that the there is no statistically significant correlations between cosmic rays and global albedo or globally averaged cloud height. Neither did they find any evidence for any regional or lagged correlations. It’s nice to see that the Guardian has picked up these findings.
Earlier in October, Almeida et al., 2013 had a paper published in Nature on results from the CLOUD experiment at CERN. They found that galactic cosmic rays exert only a small influence on the formation of sulphuric acid–dimethylamine clusters (the embryonic stage before aerosols may act as cloud condensation nuclei). The authors also reported that the experimental results were reproduced by a dynamical model, based on quantum chemical calculations.
Some may ask why we keep revisiting the question about cosmic rays and climate, after presenting all the evidence to the contrary.
One reason is that science is never settled, and there are still some lingering academic communities nourishing the idea that changes in the sun or cosmic rays play a role. For this reason, a European project was estaqblished in 2011, COST-action TOSCA (Towards a more complete assessment of the impact of solar variability on the Earth’s climate), whose objective is to provide a better understanding of the “hotly debated role of the Sun in climate change” (not really in the scientific fora, but more in the general public discourse).
Oldenborgh et al. (2013) also questioned the hypothesised link between extremely cold winter conditions in Europe and weak solar activity, but their analysis did not reproduce such claims.


  1. T. Sloan, and A.W. Wolfendale, "Cosmic rays, solar activity and the climate", Environmental Research Letters, vol. 8, pp. 045022, 2013. http://dx.doi.org/10.1088/1748-9326/8/4/045022
  2. J. Krissansen-Totton, and R. Davies, "Investigation of cosmic ray-cloud connections using MISR", Geophysical Research Letters, vol. 40, pp. 5240-5245, 2013. http://dx.doi.org/10.1002/grl.50996
  3. J. Almeida, S. Schobesberger, A. Kürten, I.K. Ortega, O. Kupiainen-Määttä, A.P. Praplan, A. Adamov, A. Amorim, F. Bianchi, M. Breitenlechner, A. David, J. Dommen, N.M. Donahue, A. Downard, E. Dunne, J. Duplissy, S. Ehrhart, R.C. Flagan, A. Franchin, R. Guida, J. Hakala, A. Hansel, M. Heinritzi, H. Henschel, T. Jokinen, H. Junninen, M. Kajos, J. Kangasluoma, H. Keskinen, A. Kupc, T. Kurtén, A.N. Kvashin, A. Laaksonen, K. Lehtipalo, M. Leiminger, J. Leppä, V. Loukonen, V. Makhmutov, S. Mathot, M.J. McGrath, T. Nieminen, T. Olenius, A. Onnela, T. Petäjä, F. Riccobono, I. Riipinen, M. Rissanen, L. Rondo, T. Ruuskanen, F.D. Santos, N. Sarnela, S. Schallhart, R. Schnitzhofer, J.H. Seinfeld, M. Simon, M. Sipilä, Y. Stozhkov, F. Stratmann, A. Tomé, J. Tröstl, G. Tsagkogeorgas, P. Vaattovaara, Y. Viisanen, A. Virtanen, A. Vrtala, P.E. Wagner, E. Weingartner, H. Wex, C. Williamson, D. Wimmer, P. Ye, T. Yli-Juuti, K.S. Carslaw, M. Kulmala, J. Curtius, U. Baltensperger, D.R. Worsnop, H. Vehkamäki, and J. Kirkby, "Molecular understanding of sulphuric acid–amine particle nucleation in the atmosphere", Nature, vol. 502, pp. 359-363, 2013. http://dx.doi.org/10.1038/nature12663
  4. G.J. van Oldenborgh, A.T.J. de Laat, J. Luterbacher, W.J. Ingram, and T.J. Osborn, "Claim of solar influence is on thin ice: are 11-year cycle solar minima associated with severe winters in Europe?", Environmental Research Letters, vol. 8, pp. 024014, 2013. http://dx.doi.org/10.1088/1748-9326/8/2/024014 
Source/fonte: RealClimate

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