Blue Collar Scientist

One of the common arguments trotted out by global warming denialists is that:

1. The sun emits cosmic rays
2. The number or energy of these cosmic rays varies with solar activity
3. The Earth’s magnetic field, and the solar wind, tend to divert cosmic rays away from the Earth
4. But when the solar wind is weak, more cosmic rays hit the Earth
5. Which creates more charged particles in the atmosphere
6. Which somehow causes more cloud formation
7. Which cools the climate
8. But when the solar wind is strong again, then the Earth warms up

This is based on the research hypothesis of Henrik Svensmark of the Danish National Space Center, so this is not a lunatic idea. What is lunatic is the way that the denialists latched on to the idea before it was tested, and presented it as fact, used it to denigrate other scientists and suggest they are fools, and so on. In real science, you come to these conclusions after the experiments have been done, not before.

But now some experiments have been done, and the hypothesis has not held up very well in testing. Several experiments and analyses have called the hypothesis into serious question over the last couple years.

Now, there’s yet another scientific study which shows that things just don’t work like that. Or at least if they do, the differences between strong and weak solar wind periods are way to small to have a noticeable effect on clouds.

The abstract is not particularly difficult, but I want to make some remarks on it anyway, so here it is with my comments interspersed:

A decrease in the globally averaged low level cloud cover, deduced from the ISCCP infrared data, as the cosmic ray intensity decreased during the solar cycle 22 was observed by two groups.

So cloud cover was observed to decrease, and cosmic ray intensity decreased; this much is known.

The groups went on to hypothesize that the decrease in ionization due to cosmic rays causes the decrease in cloud cover, thereby explaining a large part of the currently observed global warming.

This hypothesis takes advantage of the fact that many times, correlation really does mean causation. Not always - but sometimes.

We have examined this hypothesis to look for evidence to corroborate it.

Yay science! That’s how it works. Someone comes up with an idea about how things might happen, and you get a bunch of interested scientists doing experiments to see if that idea is right.

None has been found and so our conclusions are to doubt it. From the absence of corroborative evidence, we estimate that less than 23%, at the 95% confidence level, of the 11 year cycle change in the globally averaged cloud cover observed in solar cycle 22 is due to the change in the rate of ionization from the solar modulation of cosmic rays.

How does this hurt the denialists’ cause? Well, it doesn’t, because they’re denialists. Mere facts won’t get in the way of their political agenda.

But if they did respect evidence, this analysis puts an upper limit on just how strong the cosmic ray/cloud cover correlation could possibly be. And that upper limit isn’t anywhere near what is required to account for the observed climate change.

The researchers are still arguing about things, with Svensmark basically calling Terry Sloan, the PI of this study, an idiot:

“Terry Sloan has simply failed to understand how cosmic rays work on clouds,” he told BBC News.

To me, saying that a highly-qualified researcher in the same field simply doesn’t understand is a strong sign that the person saying it is on weak ground, although we don’t really know what Svensmark said that didn’t get into the BBC story. But Slaon describes the very elegant experiment that he and his co-investigators did, and it is compelling:

Professor Sloan’s team investigated the link [between cosmic rays and cloud cover] by looking for periods in time and for places on the Earth which had documented weak or strong cosmic ray arrivals, and seeing if that affected the cloudiness observed in those locations or at those times.

“For example; sometimes the Sun ‘burps’ - it throws out a huge burst of charged particles,” he explained to BBC News.

“So we looked to see whether cloud cover increased after one of these bursts of rays from the Sun; we saw nothing.”

Dang, that is good science communication. That boils a really complex and difficult series of physical processes down to something that anybody will have enough attention span to listen to. Kudos to Terry Sloan.

The experiment makes a lot of sense to me. The Earth is not a point collector of cosmic rays; different locations on the Earth gather them unequally. Cosmic rays are highly localized. We see them all the time in CCD camera images of the night sky in my asteroid research¹, and occasionally some images have a striking abundance of cosmic ray strikes that hasn’t occurred at a nearby observatory. Dedicated cosmic ray detectors show that some parts of Earth can experience a veritable storm of cosmic rays, while other parts get the usual amount.

The fact that Sloan took advantage of this well-known localization of cosmic ray strikes, and found no evidence that cosmic rays were even correlated with clouds - let alone causative - is very strong evidence against the denialists’ position.

As I mentioned above, this is probably not going to penetrate the denialists’ understanding, and will make no difference to them in terms of aggressively pursuing their scorched-earth political agenda. They’ve irrevocably burned into their mind the false notion that believing in global warming means you are an enviro-communist. They don’t understand the research, and they don’t want to. But there’s something else they don’t understand: that people can accept the evidence for global warming, and yet still want to drive gasoline-powered automobiles that pollute less. And that pursuing a vigorous domestic and alternative energy policy would result in a strong economic stimulus.

Anyway - scientific evidence is cool², and we’ve got an interesting case here.

1. They are extremely annoying, not only because of the artifact it leaves in the image, but also because you then envision these things flying through your body, which is many times larger than the CCD detector…. [↩]
2. No pun intended. [↩]

This entry was posted on Friday, April 4th, 2008 at 8:05 am and is filed under astronomy, dimwits, global warming. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.