Glaciers and Icebergs at Cape York, via wikimedia
A recent paper from the Europe-based CERN laboratory has suggested a potential link between variations in solar activity and Earth’s climate. CERN, best known for smashing atoms, is currently running an experiment to better understand the effect of galactic cosmic rays on cloud formation in the atmosphere. The first findings from this experiment, termed CLOUD (Cosmics Leaving Outdoor Droplets), were published in August in the journal Nature (full article behind a paywall- sorry to all the non-students that likely won’t be able to access it).
The experiment consisted of filling a 26.1 m3 stainless steel tube with various gases found in the atmosphere and bombarding the mixture with cosmic rays. The CLOUD team found that the cosmic rays ionized sulfuric acid particles, yielding nucleated sulfur aerosols. These aerosols are akin (but not quite identical) to particles that act as cloud condensation nuclei– particles that atmospheric water vapor typically must coalesce around in order to form clouds.
The study suggests that cosmic rays striking earth may produce cloud condensation nuclei and, therefore, more clouds. Clouds reflect incoming solar radiation, which could potentially cool the planet. It is important to note that clouds also reflect infrared radiation from the earth’s surface back down to it, warming it. The net effect of cloud cover on global temperature is not well established.
Additionally, the sun plays a role in regulating the relative amount of cosmic rays that reach earth’s atmosphere. In times of heavy solar activity, the sun’s energy is so strong that it essentially forms a bubble or barrier around the solar system, which tends to stop galactic cosmic rays (cosmic rays that originate in other parts of the Milky Way Galaxy). In times of weak solar activity, this barrier is less effective, allowing more galactic cosmic rays into the solar system.
Climate skeptics have seized upon this study to assert that fluctuations in global climate are controlled by cyclical variations in solar activity. The main claim is that recent increased solar activity has led to fewer cosmic rays and diminished cloud cover. Thus, more solar radiation is striking the earth’s surface, yielding higher global temperatures. This runs contrary to the more mainstream belief that anthropogenically-induced increases in atmospheric greenhouse gases are causing global warming.
Does this result mean that rising levels of atmospheric carbon dioxide have nothing to do with increases in global temperature? Not quite. The authors from CERN are careful to point out the limitations of the study and never make an assertion that solar activity is directly responsible for fluctuations in global temperatures (the skeptics might have noticed this if they actually read the paper). The paper does not attempt to compare historical solar activity to global temperatures either.
The study merely found that cosmic rays are capable of ionizing certain atmospheric particles to produce nucleated aerosols inside a chamber in a laboratory. The aerosols that the CLOUD team found are similar in structure to cloud condensation nuclei, but were too small to actually act as condensation nuclei. They did not directly determine that cosmic rays influence cloud formation and are not sure about these processes on an atmospheric scale.
The most reasonable thing to take away from this study is that cosmic rays may exert a noteworthy influence on particles in the atmosphere. Additional research will have to determine whether or not these rays impact the formation of cloud condensation nuclei and clouds. Any future knowledge of atmosphere-cosmic ray interactions, whether or not they render the traditional theory of anthropogenic global warming incorrect, are likely to be useful in helping produce more reliable climate and weather models, so further research into this matter is valuable.
This finding serves as a reminder that the processes controlling the Earth’s atmosphere and climate are very complex but it falls short of disproving anthropogenic global warming entirely. For now, the notions of climate change that I grew up with still pass muster.
The Central dogma of Anthropogenic Global Warming: