A couple of weeks ago, Dr. Phil Jones, the former director of the East Anglia University Climatic Research Unit and central figure in the Climategate scandal, made a few interesting comments to the press…

Climategate U-turn as scientist at centre of row admits: There has been no global warming since 1995By Jonathan Petre

Last updated at 5:12 PM on 14th February 2010[…]

He further admitted that in the last 15 years there had been no ‘statistically significant’ warming, although he argued this was a blip rather than the long-term trend.

The no “statistically significant” warming since 1995 comment certainly was a bombshell… But, what exactly does he mean by “statistically significant”?

A plot of the HadCRUT3 temperature series since 1995 certainly seems to show a warming trend…

- However, this trend is not “statistically significant.” The correlation coefficient (or r-squared) value is only 0.13. This means that only 13% of the data fit the linear trend.

- Since 1998, the data show no trend at all…

Since 2003, HadCRUT3 shows a statistically insignificant cooling trend…

One of the “problems” with the way climate data are handled is in the obsession with applying linear trend lines to non-linear data.

A Sine wave has no linear trend…

But… What happens if my data represent only a portion of a Sin wave pattern?

The r-squared of a linear trend line of this partial Sine wave is 0.88… 88% of the data fit the trend line. This implies a very strong secular trend; yet, we know that in reality Sine waves do not have secular trends.

If we take the entire HadCRUT3 series and apply a linear trend line, we get an apparent secular trend…

The r-squared is 0.55… 55% of the data fit the secular trend. This implies that there is a real long-term warming trend.

What happens to that secular trend if we expand our time series like we did with the Sine wave?

The apparent secular trend vanishes in a puff of mathematics…

How can such a clear secular trend vanish like that? The answer is easy. Each “up hill” and each “down hill” leg of a Sine wave has a very strong secular trend. Unless you have enough data to see several cycles, you don’t know if you are looking at a long-term trend or an incomplete cycle.

If we take the HadCRUT3 series and compare the the period from 1912-1945 to the period from 1975-2009, we find that they are statistically indistinguishable (a fact Dr. Jones acknowledged in the Mail article)…

We also find that Moberg’s Medieval Warm Period reconstruction is very similar to the HadCRUT3 series…

Using the GISP2 ice core data from central Greenland we can see that over the last 50,000 years, there have been statistically significant warming trends…

And there have been cooling trends of varying statistical significance…

What does all of this mean?

It means that the Earth’s climate is cyclical. It means that the climate changes we’ve experienced over the last 150 years are not anomalous in any way, shape, fashion or form.

February 23, 2012 at 12:06 |

Your big problem here is that you’re conflating local temperature records (GISP2) with various global records. We expect to see exaggerated warm period in local records like GISP2 because they are local. You will also find what are called “anti-phase” events in other, usually southern, records for every warm record in GISP2. In fact, if you compare GISP2 to the Vostok (Antarctica) record you can clearly see the anti-phase events that correspond to the warming events you’re pointing out.

As well, it’s completely irrelevant whether past trends are similar in magnitude. What matters is the forcing that is producing the trend and what can be projected as a result of that forcing.

Take early 20th century warming for instance. We know the greenhouse gas forcing was less during that period, but we also had increasing solar forcing and reduced volcanic activity. In the past 30 years we’ve had falling solar forcing. Estimates suggest that absent anthropogenic greenhouse gas forcing we should have seen slight cooling over the past 30 years.