There. I said it.

Wrong about what, you wonder? During an interview for the BBC he was asked, “Do you agree that from 1995 to the present there has been no statistically-significant global warming?” Jones replied, “Yes, but only just.”



Sorry, Phil, I disagree.

Jones based his statement on straightforward analysis of the data and reported his result honestly. The HadCRUT3v data set (which is from Jones’s institution) shows warming since 1995, but it’s not statistically significant. But then, climate trends over such short time spans (yes, for climate 15 years is a short time span) don’t usually pass statistical significance tests.

But by removing the influence of exogenous factors like el Nino, volcanic eruptions, and solar variation (or at least, approximations of their influence) we can reduce the noise level in temperature time series (and reduce the level of autocorrelation in the process). This enables us to estimate trend rates with greater precision. And when you do so, you find that yes, Virginia, the trend since 1995 is statistically significant. And that’s true for all 5 major data sets, including the HadCRUT3v data set from Phil Jones’s organization.

Let’s analyze the adjusted (exogenous-factor-compensated) data we got from our last analysis. We’ll first fit a trend line since 1975 to estimate the autocorrelation of the noise. Then we’ll estimate the warming rate (and its probable error) by linear regression on the data from various start years to the present, for all start years from 1975 to 2005.

Here’s the adjusted data based on the HadCRUT3v data set:

Here are the warming rates estimated from each starting year to the present:

Note that until 2001, the error bars (which are 2-sigma) don’t include the possible value zero. Therefore, until 2001 the warming is statistically significant (using the usual de facto standard in statistics).

Not only is the warming since 1995 statistically significant, the warming since 2000 is as well!

The same result emerges from the analysis of adjusted data from NASA GISS:

Certainly, we shouldn’t fault Jones for not estimating the influence of exogenous factors when computing warming rates and their statistical significance. His analysis was straightforward and standard, and his statement was scientifically conservative (which is a common practice among scientists).

Just as certainly, we should fault those who claim that Jones’s “not statistically significant” statement means “not warming.” For most of those who do so, it’s not even an honest mistake.