December 19, 2017

expert reaction to study looking at cosmic rays, cloud formation and climate

Scientists publishing in Nature Communications investigate the link between exploding stars, clouds, and climate on Earth.

Dr Hamish Gordon, Post-doctoral researcher, Institute for Climate and Atmospheric Science, University of Leeds, said:

“The press release (from the Technical University of Denmark) states that about 5% of the growth rate of new aerosol can be due to ions, which is the main result of the article.  Of itself, this is an interesting and plausible result, and if it stands up to more detailed scrutiny it may prove an important contribution to aerosol microphysics.  However, it is very far from “the last piece of the puzzle explaining how particles from space affect climate on Earth”.  While the authors calculate rates of condensation and growth, there are no calculations or modelling of how their results might influence particle concentrations in the atmosphere.  Even if this link could be established, there is still a complicated modelling step, fraught with uncertainties, to calculate how atmospheric particle concentrations might influence climate.

“There are strong negative feedbacks involved in aerosol-climate interactions, some of which are referred to by the press release: particles must grow “nearly a million times in mass” to affect clouds.  As most of the particles end up sticking to existing cloud seeds rather than forming new ones, only a small fraction of ions end up making a difference.  In today’s atmosphere, ion concentrations only change by a few percent every few decades.  While the effects on particle growth studied in this article were not accounted for in previous atmospheric modelling studies, the effects the authors find are actually quite small – 5% will make relatively little difference – and so this article is still unlikely to change the conclusion of previous studies, that the effects of changing ion concentrations on cloud seeds are negligibly small in the present day atmosphere.

“Thus, to say a “missing link” has been found, implying that observed cosmic-ray-climate correlations can now be fully explained, is premature.”

* ‘Increased ionization supports growth of aerosols into cloud condensation nuclei’ by H. Svensmark et al. published in Nature Communications on Tuesday 19 December 2017.. 

Declared interests

None received.