Cosmic Rays, Clouds and Climate

For some reason I am still not sure of I ended up this afternoon on the wordpress homepage and one of the featured blogs was last year's weblog award winner for best science blog What's Up With That (WUWT).

If you have never come across this blog before, and I have only ever heard about it in passing, they are of some what of a climate change denialist point of view (which as Phil mentions in that last link just shows that all the webbies are is a popularity contest rather than an evidence based award). The post that was front and centre on the blog was this one about the relationship between cosmic rays and cloud formation. What really caught my attention was the juxtaposition between the "headline": Message in the CLOUD for Warmists: The end is near?, and the graph that followed the first paragraph.

Now the paragraph (and actually the graph) talk about the correlation between cosmic rays (using various isotopes as a proxy) and temperature. Much of the rest of the post is a quite interesting description of the CERN experiments and hypothesis that links the galactic cosmic rays (GCR) and cloud formation, and while that is all interesting it is irrelevant to what I wanted to say, even if this turns out to be correct.

Now if you look closely at the graph you can see that it covers the last almost 800 years and the proxies for the GCR (¹⁰Be and ¹⁴C which are the blue and black lines) correlate very well with the red line (Siberian Temperature). They track each other quite well through the dark ages and into the medieval warm period and even through the maunder minimum (little ice age) right up until the middle of the 19^th century. Now once we get to the late 19^th century we see that the temperature continues to rise and the other lines level off a bit - you can still see that there is a slight influence with the dip in temperature around early to mid 20^th century but the lines in general are no longer closely correlated.

Oops! Maybe if you are going to make an argument you should make sure that your strongest piece of evidence does not plainly and in clear sight contradict your argument.

What does that all mean, firstly well it looks remarkably like the temperature and sunspot cycle length plot I showed previously and as I stated in that post what we can see is an excellent correlation spoiled since the industrial revolution. I left a comment on the WUWT blog that outlined the above lack of modern correlation and stated that what has happened since the industrial revolution that we know may have caused this warming, well we have been putting out a lot of CO₂.

Other commenters on the WUWT blog mention that CO₂ is a very minor atmospheric constituent and that H₂O is a better green house gas and much more prevalent. Well this is also true, however H₂O has some rather interesting behaviors it saturates quite easily in the atmosphere and everyone that does not live in desert (or at least a drought) gets to experience this - RAIN! Also if you have ever been to the tropics, you may have noticed that the rain can be quite heavy when it is warm this is because increasing the temperature allows the atmosphere to hold more water.

If water vapor itself was enough to trigger the sort of greenhouse effect that we are seeing then we would have long ago passed the point of now return, but fortunately the saturation of water in the atmosphere (what we call 100% relative humidity) seems to prevent this from happening - although this is not to say that when the temperature does get warm that there will be more water in the atmosphere which will probably on lead to worse storms etc rather than any large feedback effect (which means I had to write a retraction since I claimed that there may have been an H₂O feedback in my original comment on WUWT - ooops gotta think the consequences through more).