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It’s getting hotter – despite cooling from cosmic rays

Posted on 16 April 2013 by Uma Jha

This article was written by a student in the Science Communication program at the University of Western Australia. In the unit, Introduction to Scientific Practices, students learn how to effectively present scientific information for different audiences. As part of the process of learning to distil complex science into simple, engaging formats, structured tutorials are given on how to use The Debunking Handbook. This article was submitted as part of an assignment on writing an engaging article for a non-specialist audience.

Unlike global warming, avoiding blame is entirely natural. After all, who wants to be told that they are causing climate change? Unfortunately, the fact is that we are – a fact that if ignored will cause problems for future generations. But these days, people try to excuse themselves by blaming uncontrollable external forces. Take cosmic rays, for example: high energy charged particles, hurtling from outer space towards the earth at nearly the speed of light. Cosmic rays can almost seem like the stuff of science fiction, and perfect for the blame game.

The Excuse

How exactly could cosmic rays change global temperature? The answer is that cosmic rays might play a part in cloud formation. If they do help with cloud formation, more cosmic rays would cause more clouds to form. The opposite would also be true – if there are fewer cosmic rays, there would be fewer clouds. Clouds do two things: firstly, they absorb heat and radiate it back to the earth’s surface (warming it), and secondly, they reflect heat from the sun away from the earth (cooling it). The total effect of clouds tends to be cooling, because the second effect dominates during daytime.

So, if cosmic rays are to blame, we should be seeing a decrease in cloud cover, caused by a decrease in cosmic rays. Why would this be happening? The culprit offered is the sun’s powerful magnetic field, which deflects cosmic rays. If it is getting stronger, fewer cosmic rays would reach the earth, so less cloud cover would form.

This sounds plausible, but can it be tested? Yes, by comparing the records for two aspects in question. And they have been, by researchers from universities and specialist institutions around the globe.

Undone by the Data

Current research has shown that cosmic rays cannot be the cause of recent global warming. So why do some people claim that they are? Old data has proven to be  deceptive in this area.

The first question that needs to be asked, is do cosmic rays really form clouds? There seemed to be a strong link between cosmic rays and low lying cloud cover – until 1991, when cloud cover (which should react within a few days) began to lag behind cosmic ray counts by more than 6 months. After 1994, the link broke down completely.

Different studies also find issues with this link. Cosmic radiation varies more in high latitudes such as the Polar Regions. If there is a link, these regions should see more variation in cloudiness. However, this is not seen.

So it seems like cosmic rays might not help to form clouds after all. Is there any relationship between cosmic rays and global temperature at all? The fact is that there has been no such relationship for the past 30 years. Before the 1970s, temperature did seem to follow levels of cosmic rays. This is what caused some scientists to believe that there was a relationship between the two. After the 1970s, this relationship broke down. For the next 15 years, changes in temperature were happening before changes in cosmic rays. After this, temperature and cosmic ray counts moved in opposite directions.

But wait, there’s more – cosmic rays cannot easily be used to explain effects such as nights warming more than days, and the upper atmosphere cooling. At this point, you are probably wondering if there is any truth to the excuse at all. What about the sun’s magnetic field? Well, over the past 30 years, its strength has not really changed – no reprieve here.

An Excuse past its Use-by Date

So now we have seen how outdated data gave life to the ‘it’s cosmic rays’ excuse. But supposing they did influence global temperature, what effect would cosmic rays be having? Research comparing global temperatures to levels of cosmic ray related substances shows that cosmic ray levels are increasing – even beyond previously predicted levels. And here is the final nail in the coffin for this excuse: If we finally conclude that cosmic rays do have an effect on global temperature, for the past few decades, it will likely turn out that cosmic rays have been cooling the earth – not warming it.


Clouds, Cloudiness, Surface Temperature, the Greenhouse Effect and Global Climate Change.   Retrieved 3/4/2012, from

Cosmic Rays - Introduction. (3/2/2010)  Retrieved 3/4/2012, from

What's the link between cosmic rays and climate change?   Retrieved 3/4/2012, from

Kristjánsson, J. E., Kristiansen, J., & Kaas, E. (2004). Solar activity, cosmic rays, clouds and climate–an update. Advances in space research, 34(2), 407-415.

Krivova, N. A., & Solanki, S. K. (2003). Solar total and spectral irradiance: modelling and a possible impact on climate.

Kulmala, M., Riipinen, I., Nieminen, T., Hulkkonen, M., Sogacheva, L., Manninen, H. E., . . . Aalto, P. P. (2009). Atmospheric data over a solar cycle: no connection between galactic cosmic rays and new particle formation. Cosmic rays, 9, 21525-21560.

Laut, P. (2003). Solar activity and terrestrial climate: an analysis of some purported correlations. Journal of Atmospheric and Solar-Terrestrial Physics, 65(7), 801-812.

Lockwood, M., & Fröhlich, C. (2007). Recent oppositely directed trends in solar climate forcings and the global mean surface air temperature. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Science, 463(2086), 2447-2460.

Mewaldt, R. A. (1996). Cosmic Rays.  Retrieved 3/4/2012, from

Miyahara, H., Yokoyama, Y., Yamaguchi, Y., & Nakatsuka, T. (2010, 2010). Variability of cosmic rays and its influence on climate change at the multi-decadal time scale. Paper presented at the 38th COSPAR Scientific Assembly, Bremen, Germany.

Sloan, T., & Wolfendale, A. W. (2008). Testing the proposed causal link between cosmic rays and cloud cover. Environmental Research Letters, 3(2), 024001. doi: 10.1088/1748-9326/3/2/024001

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Comments 1 to 3:

  1. Granting my layperson status, but from what I have seen, cosmic rays affecting the climate is a roundabout form of the Sun affecting the climate (since cosmic ray incidence upon the Earth appears to be modulated by solar activity).

    One notes the text in the OP describes:

    Before the 1970s, temperature did seem to follow levels of cosmic rays. This is what caused some scientists to believe that there was a relationship between the two. After the 1970s, this relationship broke down. For the next 15 years, changes in temperature were happening before changes in cosmic rays. After this, temperature and cosmic ray counts moved in opposite directions.

    and this appears to coincide with an identical relationship between changes in TSI and changes in global mean temperature, a relationship that experiences a similar breakdown over the same time frame.

    So the bottom line seems to me that if the influence cosmic rays have on Earth climate follows from solar influence, rather than acting independently, then given solar activity & Earth climate are no longer conjoined, it follows that cosmic ray activity and & Earth climate will also no longer be conjoined.

    (Unrelated formatting note: the phrase "And here is the final nail in the coffin for this excuse" appears twice in the final paragraph before the bibliography section.)

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  2. Composer - correct.  Galactic cosmic ray flux on Earth is dictated by the solar magnetic field strength.  Higher solar activity means a stronger solar magnetic field, which means more GCRs deflected, meaning fewer GCRs on Earth, and hypothetically less cloudcover and thus more warming.  GCRs are hypothetically basically a solar amplifier.

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  3. It's seems that a blast of cosmic radiation struck the earth in 774AD, apparently without any climatic effects, or at least only short term ones.

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