Climate Change Q&A

The BBC has a Q&A with Phil Jones, director of the Climatic Research Unit (CRU) at the University of East Anglia (UEA).

I found it very interesting, and recommend people read it. He is very upfront on what do know, and do not know, and what periods of warming have and have not been significant, such as:

As for the two periods 1910-40 and 1975-1998 the warming rates are not statistically significantly different (see numbers below).

and

B – Do you agree that from 1995 to the present there has been no statistically-significant global warming

Yes, but only just. I also calculated the trend for the period 1995 to 2009. This trend (0.12C per decade) is positive, but not significant at the 95% significance level. The positive trend is quite close to the significance level. Achieving statistical significance in scientific terms is much more likely for longer periods, and much less likely for shorter periods.

C – Do you agree that from January 2002 to the present there has been statistically significant global cooling?

No. This period is even shorter than 1995-2009. The trend this time is negative (-0.12C per decade), but this trend is not statistically significant.

So from 1995 to 2009, there has been warming, but not at a level to be deemed significant, and likewise from 2002 to 2009 there has been cooling but not at a level to be deemed significant.

What this signifies to me is that the data over the next five years or so will be very important – it may either push the post 1995 era into significant warming, or the post 2002 era into significant cooling. The chances of post 2002 era being a statistically significant cooling are less, as it is a shorter period.