Climate’s Cosmic Connection?

by Bill Chameides | September 12th, 2011
posted by Erica Rowell (Editor)

Permalink | 2 comments

Meet the cosmic Rays. Could they be the cause of global warming? Let’s talk it over.

Did European scientists from CERN find that cosmic rays caused global warming?

This is a story about a science paper recently appearing in the journal Nature that’s had some pretty good legs in the media. The paper, authored by scientists led by Jasper Kirkby of the European Organization for Nuclear Research (better known as CERN), reported on the results of an experiment using CERN’s Proton Synchrotron Accelerator.

Now, as a rule, experiments involving accelerated protons do not get a lot of media attention. But this one’s a little different because it suggests there may be a connection between the energetic particles that bombard the Earth from space known as cosmic rays and climate.

CERN’s ‘CLOUD’ Experiment

The experiment sent subatomic particles streaming though and crashing into atmospheric molecules inside a sealed chamber outfitted with advanced instrumentation capable of monitoring the results of all those collisions. The purpose of the experiment was to see if ionized (that is, positively and negatively charged) molecules produced from the collisions would lead to the formation of tiny particles known as cloud condensation nuclei.

Before going any further, I fear some of you may be confused by all the particle references flying around here. We’ve got two distinct types of particles: subatomic particles — really, really small stuff like protons and neutrons that make up a single atom — and tiny atmospheric particles called cloud condensation nuclei, which are clusters of many, many molecules. Now, recall that molecules are made up of one or more atoms. So even though we call cloud condensation nuclei “tiny” — and at less than one-millionth of a meter in diameter they are tiny — they’re still a whole lot bigger than subatomic particles.

What does this have to do with climate? Well, cloud condensation nuclei form clouds and in doing so help determine the reflectivity of clouds. The reflectivity of clouds affects the amount of energy the Earth absorbs from the Sun. So, if subatomic particles from the Proton Synchrotron trigger the formation of cloud condensation nuclei in a sealed chamber, then maybe cosmic rays can form cloud condensation nuclei in the atmosphere. And if that is the case, then a change in the amount of cosmic rays hitting the Earth could cause the climate to heat up or cool down. (For more on cosmic rays and the Sun, see this earlier post.) Note that there are a lot of ifs between a positive result in the experiment and the conclusion that cosmic rays affect climate, but still, all in all, a fascinating hypothesis and experiment.

As it turns out, Kirkby et al did get a positive result: Increases in ionization from subatomic particles coming from the Proton Synchrotron did increase cloud condensation nuclei formation; however, the relationship depended critically on the presence of sulfuric acid and ammonia. Moreover, the ionization flux in the CERN experiments was varied by a factor of two or more to produce discernible changes in condensation nuclei formation, and cosmic rays typically vary by only about 10 to 20 percent. So maybe there is a link between cosmic rays and cloud reflectivity, but this experiment does not provide definitive proof.

There are those in the media and in the refudiater camp (see for example here and here) who have been hailing this finding as evidence that climate scientists have had it all wrong and human activities are not, after all, a cause of global warming.


What Do the Authors Say About ‘The Controversy’?

Kirkby et al are aware that their work is relevant to a controversial subject. For example, you will find this statement in their paper:

“The … measurements address a long-standing controversy.”

But the controversy referred to here is not the one you’re probably thinking of. It’s the controversy in:

“atmospheric nucleation, namely whether binary nucleation of sulphuric acid and water vapour can account for new particle formation in the boundary layer.”

For many atmospheric scientists this paper and its results are an important subject (you can learn more about it here [pdf] or if you don’t have a subscription here), but its connection to how cosmic rays might cause global warming is tenuous at best.

Fact: Kirkby et al never speculate about or even mention a possible connection between cosmic rays and the current global warming.

Could Cosmic Rays Be Causing Global Warming?

Climate is influenced by any number of factors in addition to greenhouse gases. These include the Sun’s radiative output and ocean circulation. The work of Kirkby et al provide increased evidence that cosmic rays should be included in that list.

That is indeed a significant finding, but it’s a huge leap to infer that cosmic rays are a cause of the global warming we’ve witnessed over the past several decades.

For that to be the case, even if one accepts that there is a cosmic ray/climate connection, the cosmic ray flux would have to have changed over the period of the warming; more specifically, it would have had to have decreased in order to have caused a decrease in the Earth’s reflectivity. We know for a fact that that has not happened. As illustrated below, the cosmic ray flux goes up and down with the 11-year solar cycle, but there has been no net change in the flux since the 1950s. End of story.

So, did European scientists from CERN show that global warming is due to cosmic rays?


The blue curve is a measure of the change in the cosmic ray flux. The yellow curve plots the change in solar sunspot number. Note that there is an inverse relationship between the two. The less active the Sun, the more cosmic rays penetrate through the solar wind and impinge on the Earth. (Source: Chart by NOAA based on data from the Climax, Colorado, neutron monitor operated by the University of Chicago)

Correction: September 12, 2011, 1:30 pm.
This post was revised to correct a typo in the name
of the paper’s lead author.

filed under: climate change, faculty, global warming
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  1. John Hartz
    Sep 12, 2011

    Perhaps caused by the effects cosmic rays on the human brain, or ESP, a similar article was posted today on the Skeptical Science (SkS) website. “CERN – Saying Nothing About Cosmic Ray Effects on Climate” covers much of the same ground as does the above article, but also includes an original, 3-panel cartoon spoofing the deniers’ common refrain, “This is the last nail in the AGW Theory coffin.” To access the SkS article, go to:

  2. K.M. Hurley
    Sep 12, 2011

    Excellent, thoughtful piece — refreshing clarity. We all suspect that cosmic influencers affect our ecosystem. Of course they do. And we’d like to believe that ecosystem changes are in cosmic hands, beyond our control. Of course they’re not. Thanks for writing.

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