Another divergence problem
Nov 7, 2008
Bishop Hill in Climate

Steve McIntyre has pointed out before that paleoclimatologists actually have two divergence problems rather than one. Most people who follow the climate debate are aware of the fact that tree ring widths have not responded to the rise in temperatures in the second half of the twentieth century, a fact which completely undermines the case for their use as proxy thermometers. This inconvenient truth has been neatly avoided by simple dint of not reporting any proxy data later than 1980, truncating the series where necessary.

The second divergence problem is the fact that tree ring widths, and ring wood densities (which are also used in temperture reconstructions), having tracked each other quite well through most of the record, have also diverged in recent decades. Here the solution here has been to "adjust" the record, pretending that the divergence never happened.

Now (and I'm grateful to a reader for pointing this out to me) the BBC has reported a study in Science which has analysed a Chinese stalagmite and has linked its growth to the Asian monsoon.

The monsoon record also matched up nicely with the advance and retreat of Swiss glaciers.

Scientists say the natural archive shows that climate change can have devastating effects on local populations - even when this change is mild when averaged across the globe.

In the cave record, the monsoon followed trends in solar activity over many centuries, suggesting the Sun played an important role in the variability of this weather system.

To a lesser extent, it also followed northern hemisphere temperatures on a millennial and centennial scale. As temperatures went up, the monsoon became stronger and, as they dropped, it weakened.

Great. More evidence that we're going to be fried alive very shortly. But wait, what's this?

However, over the last 50 years, this relationship has switched.

Oh, oh! Start thinking up stories to explain it guys....

The researchers attribute this to the influence of greenhouse gas emissions and sulphate aerosols released by human activities.

That should do it. Another divergence problem neatly disposed of.



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