This may be well known to those who follow solar activity closely, but
this summary of a new paper on recent sunspot activity on The Register
was an interesting read:

http://www.theregister.co.uk/2011/06/14/ice_age/

The regression line looks too steep to my eye though I dare say that's
an optical illusion and it's been calculated accurately enough. But
even so the regression line looks fairly sensitive and another year
with higher than expected sunspot activity might well lower the slope.

JGD