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Saturday, 15 September, 2007

Do 500 scientists refute anthropogenic global warming?

The latest attack on global warming consensus comes from Dennis Avery and Fred Singer who claim to have found 500 peer reviewed papers refuting that the last few decades of global warming are primarily anthropogenic. Previous attempts to find peer reviewed skeptic studies tend to miscategorise as skeptic despite the intent of the author or indeed the content of the paper. Avery and Singer appear to carry on this tradition.

While their press release peddles many skeptic myths (which I'm sure I'll be covering in future posts), the major theme is that over 300 studies have found climate has changed in the past and/or that the sun is connected. Tamino at Open Mind does a good job explaining the 1500 year natural cycles (or Dansgaard-Oeschger events) along with some useful links to relevant peer reviewed studies. I've also touched on the notion that climate has changed naturally in the past so it must be natural now.

My personal hobby horse is the sun's connection to global warming (or lack thereof). I would've thought the empirical data and many studies on the topic had long put this baby to rest but going on the long line of comments, the facts don't seem to have made a dent in the misconception. Blaming climate change on the sun is intuitive - to paraphrase the Great Global Warming Swindle: "me small... sun big". Hard to refute that kind of barnstorming logic. Nevertheless, I'll have another crack at breaking down the logical steps of why we know solar variations aren't causing global warming:

1. The sun has closely correlated with temperature in the past and been a major driver of climate
2. The correlation ended in the 70's when the modern global warming trend began
3. Therefore the sun cannot be the driving force of global warming over the past few decades

In other words, all the studies showing past correlation between solar activity and temperature only serve to emphasise the fact that the correlation no longer exists. Rather than refute the consensus, they reinforce it.

The other debate raging in the sun comments is whether the sun has been getting hotter in the past few decades. No matter how you look at the data - whether you use PMOD or ACRIM, whether you compare maximums or minimums or take 11 year averages, there is still no correlation between sun and climate. The fact that we're arguing about whether there's a slight cooling trend, a slight warming trend or no trend at all underscores the sharp divergence between sun and temperature over the past 30 years.

Posted by John Cook at 13:58 PM