Wednesday, February 21, 2007

It's curtains for cosmic rays

The recent main-stream media frenzy over the ‘cosmic ray theory of climate change’ has shown no sign of abating. For wing-nuts the world over it is proof-positive that AGW is one giant hoax; human activity isn’t mainly responsible for recent climate change and the IPCC is part of a huge conspiracy that ignores non-conforming science etcetera etcetera.

Unfortunately for cosmic-rayers, the more the studies backing the theory are investigated, the more problems with data sets and experimental methodology that pop up.

A new paper by Evan et al. in Geophysical Research Letters may well be the final nail in the coffin for cosmic ray-induced climate change. Central to the theory are data from the International Satellite Cloud Climatology Project (ISCCP) showing that cloud levels have decreased by up to 4% over the past 20 years. Decreased low-level cloud cover due to decreased cloud-nucleating cosmic rays is proposed to lead to warming. However, for some time it has been noted that a portion of ISCCP data did not match surface-based observations, and that low-level cloud cover may not have actually reduced in recent times.

When Evan and team investigated the ISCCP D2 data set they found that cloud-cover almost immediately dropped when satellites were moved and the angle at which they observed cloud-cover was reduced. The reason for this is that as more weather satellites were put into orbit, each satellite had a smaller area to observe and could look directly down through the cloud layer, rather than covering a larger area where the edges are observed at an increased angle. The latter, more direct observations made it appear as though there was less cloud when, in fact, cloud-cover hadn’t changed. The data appeared to contain observational artefacts that weren’t corrected for before use in other studies.

The paper’s concluding paragraph is devastating:
We have demonstrated that the long-term global trends in cloudiness from the ISCCP record are influenced by artefacts associated with satellite viewing geometry. Results from earlier studies based on these trends may be influenced by these non-physical artefacts, and we therefore suggest that development of a correction for the data is warranted. As the number of publications on the subject of climate change continues to grow [Stanhill, 2001], this paper highlights the need to critically explore the source of any trends in global, multi-decadal satellite data sets.
Evan’s work has yet to be reproduced and the exact extent to which the change in observation area has artificially changed cloud-cover over the past 20 years quantified. Still, things are looking decidedly grim for cosmic ray-induced climate change, which will probably end up in the dust-bin with the similarly artefact-ridden ‘troposphere isn’t warming’ theory.

Will this stop the crazies harping on about it?

Not a chance.