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If you want to question the understanding of our climate built up through more than a century of observation and experimentation, you must do two things. One is to show that this understanding is somehow fundamentally limited. The second is to provide an alternative explanation for the patterns in the climate.
One of the ideas that seemingly fits the bill is a connection between radiation and clouds. Ionizing radiation from cosmic rays and other sources can create ions in the atmosphere, which can then attract water molecules. These would form the building blocks of clouds, which would then affect the climate. The amount of radiation reaching the atmosphere does change, in part because the sun’s magnetic field, which shields Earth from incoming radiation, varies over time.
Put these ideas together and variations in the sun’s magnetic field can affect climate. It’s a nice idea, but CERN’s latest paper should finally put it to rest. (But it probably won’t be.)
The idea of cosmic ray clouds affecting climate has a few advantages. First, there is some evidence that past climate changes were associated with changes in solar activity. Of course, that would include the light the sun sent our way, but the changes in the incoming radiation wouldn’t be enough to drive the amount of change that happened. This leaves open the prospect that the sun has additional influence on the climate, for example through the strength of its magnetic field.
We already know that the magnetic field can protect us from ionizing radiation. So if the resulting ions can form clouds, the sun’s activity can affect the clouds. A few people found a connection between the incoming radiation and clouds, and we already knew that clouds can influence the climate. For some people on the internet, that was enough to argue that the sun controls everything and that humans have an insignificant influence on the climate.
Of course, that was always the best case for the influence of the sun. Looking more closely at the relationship between incoming radiation and cloud cover generally found no relationship at all; meanwhile, temperatures continued to rise even as solar activity declined. Plus clouds have a complex relationship with climate, reflecting sunlight or insulating the planet, depending on their location and structure.
Finally, it was never entirely clear that radiation could cause cloud formation at all.
That last point is where CERN, the people who built the Large Hadron Collider, stepped in. They are very adept at creating radiation in a controlled environment and thought they could get to the bottom of how that radiation might affect cloud formation. Preliminary results seemed promising, but later it turned out that the presence of even traces of chemical contaminants could completely overwhelm the influence of the radiation.
Now the same team is back with a follow-up paper that takes a closer look at the big picture of cloud formation. After years of testing, the team exposed water vapor to different conditions: different temperatures, the presence of different chemicals such as sulfuric acid and ammonia, and the presence or absence of radiation. In each condition, the number of particles on which water condensed was measured.
This allowed the team to build a model of what happens in the actual atmosphere. If you add the conditions of the atmosphere to the model – different levels of chemicals and radiation at a given temperature – it can predict the extent of cloud droplet formation. The model was compared with field measurements and it turned out to be quite accurate.
The authors then started taking different factors out of the model and seeing how well it worked. This allowed them to identify which factors had the greatest influence on cloud formation.
Most of the effect on cloud particle formation is driven by sulfuric acid, ammonia, or molecules from a biological source. Although ions are often present in these particles, they are not major drivers of this process. “The relatively weak dependence on ion concentrations,” the authors conclude, “indicates that, for the processes studied, variations in cosmic ray intensity do not significantly affect climate via nucleation in the current atmosphere.”
Really, given all the other information that has come in, this should be the end of the line for the idea that cosmic rays control our climate. But many academics find it hard to give up ideas they love. And in this case, there is a section of the public that would like to believe them.
Science2016. DOI: 10.1126/science.aaf2649 (About DOIs).
Frame image by Tom Oliver