Why Cosmic Rays do not directly affect climate

March 3, 2010 by jason

There are many reasons for the climate to change, but increases in the energy of cosmic rays warming up the atmosphere is not one of them. Yet for some reason, every debate on climate change at some stage gets onto the topic of cosmic rays and their role in global warming. I think it is important to address this because many people dismiss a lot of scientific evidence for other causes of global warming (such as changes in ice coverage or greenhouse gas concentrations) by simply attributing it to some spike in cosmic rays that may or may not have occurred at the same time. This article looks at the effects of cosmic rays directly on climate, not other secondary effects. For a further look into this topic please read my article on Cosmic Ray Levels and their effect on climate through cloud formation.

For those of you just getting in on the debate, who might not know exactly what I'm talkign about, let me start by explaining what cosmic rays actually are.

Cosmic Rays

Cosmic rays are particles impeding on the earth's atmosphere and magnetic field. These particles consist almost entirely of alpha particles (Helium nuclei) and protons (hydrogen nuclei). NASA divides cosmic radiation into 3 types:

• Galactic Cosmic Rays - Originating from deep space
• Anomalous Cosmic Rays - Originating from the edge of the heliopause
• Solar Energetic Particles - Originating from the sun.

source: NASA - Cosmic Rays

The amount of radiation actually reaching the earth is governed by the strength of the earth's magnetic field, and since the earth's magnetic field is always in flux, we experience fluctuations in the amount of cosmic radiation reaching our planet.

Some argue that this fluctuation is a possible cause for global warming - one that would be completely out of our control. I will show you that this is not the case, and that Cosmic rays have never (at least in the past 40,000 years) had a significant direct impact on the earth's climate.

Data for the analysis

In order to demonstrate the relative (lack of) effect of cosmic rays on the global climate, I will make use of data from 2 separate atmospheric datasets:

• The EPICA Ice Core Dataset - D18O isotope information about temperature
• Greenland Ice Core Project (Journal of Geophysical Research (102:26699-26706)) - 10Be isotope information about solar radiation levels

Getting information about cosmic ray levels

Having already written an article on the EPICA Ice Core and how one goes about creating a history of global temperature levels, I will give a brief introduction on how cosmic ray levels are measured.

Basically, cosmic rays collide with particles in the atmosphere, creating isotopes. Among the millions of particles that can be created in this process, some of them have both a relatively common rate of occurrence as well as having a long and measurable half-life. These particles can then be used as a measure for the amount of radiation that hit the earth at that time. The two most common particles used to date back cosmic ray levels in this manner, are the isotopes 10Be and 36Cl. This is, of course, assuming that there are no other mechanisms affecting the levels of these isotopes. To illustrate that isotope measurements from the Greenland Ice Core Project (GRIP) can be used to effectively measure cosmic ray levels, we can simply plot the occurrence of these isotopes against Mediterranean radionuclide levels - a known method for testing cosmic ray levels:

As you can see, the correlation is clear: 10Be isotope concentrations are a good indicator for cosmic ray levels.

Comparing Cosmic Ray Levels against Global Temperature

To show whether or not variations in cosmic ray levels can directly increase the temperature of our planet significantly, the next step is to plot the cosmic ray levels (obtained from the GRIP through the Journal of Geophysical Research (102:26699-26706)) against global temperature records (EPICA Ice Core Records):

Note the clear lack of a correlation between cosmic ray levels and temperature. In fact, cosmic ray levels were at their lowest about 2000 years ago, roughly the same time that globals temperatures were peaking. This really should settle the debate, as it clearly illustrates that cosmic ray levels are not a significant direct driver in global temperatures. For a closer look at other effects of cosmic rays, read my article on Cosmic Ray Levels and their effect on climate through cloud formation