The Leaked AR5 Report And Global Temperature

  • Date: 18/12/12

Model Projections


Whatever one’s view about the leaking of the draft IPCC AR5 report it does make fascinating reading, and given the public scrutiny it is now receiving it will be interesting to see what parts of it are changed when the final report is released in a year or so.

One part of it that should be changed is the section on global surface temperature data and its interpretation.

The analysis of global combined land and ocean surface temperature in AR5 is inadequate for what it admits is seen as the prime statistic of global warming. It is highly selective in the references it quotes and in the use of time periods which obscures important, albeit inconvenient, aspects of the temperature data. It is poorly drafted often making a strong assertion, and then somewhat later qualifying if not contradicting it by admitting its statistical insignificance. This leaves the door open for selective and incomplete quoting.

In Chapter 2 the report says that the AR4 report in 2007 said that the rate of change global temperature in the most recent 50 years is double that of the past 100 years. This is not true and is an example of blatant cherry-picking. Why choose the past 100 and the past 50 years? If you go back to the start of the instrumental era of global temperature measurements, about 1880 (the accuracy of the data is not as good as later years but there is no reason to dismiss it as AR5 does) then of the 0.8 – 0.9 deg C warming seen since then 0.5 deg C of it, i.e. most, occurred prior to 1940 when anthropogenic effects were minimal (according to the IPCC AR4).

AR5 admits that of the warmest years on record the “top ten or so years are statistically indistinguishable from one another.” This is sloppy. The “or so” is significant and should be replaced with a more accurate statement. Despite the admitted statistical indistinguishability of the past ten years (at least) AR5 then goes on to say that 2005 and 2010 “effectively” tied for the warmest years! There is no mention of the contribution to global temperature made by the El Nino in those years!

It is in its treatment of the recent global temperature standstill that AR5 is at its most unevenhanded. It says that much attention has been focused on the “apparent flattening in Hadcrut3 trends,” and it says that “similar length phases of no warming exist in all observational records and in climate model simulations.”

No it hasn’t. The IPCC says that the time when anthropogenic influence dominated began between 1960-80. AR5 takes 1979 – 2011 as a period for analysis when temperatures started rising after a 40-year standstill. The fact that is obvious from the data is that the past 16 years of no global temperature increase is unusual and is not an “apparent flattening.” It is a total flattening for 16 years (as AR5 confusingly admits later on), just over half of the duration of the recent warming spell. Flat periods have existed before but they were in the era when mankind’s influence was not significant. The 16-year flatness since mankind has been the prime climatic influence has been the cause of much discussion in the peer-reviewed literature, something that this AR5 does not reflect.

AR5 goes on to say that with the introduction of Hadcrut4 (and its inclusion of high latitude northern hemisphere data) there is now a warming trend. No it isn’t. Look at the Hadcrut4 data and, as the GWPF has demonstrated, it is warmer than Hadcrut3, but it is also flatter for the past 15 years. AR5 also adds that “all products show a warming trend since 1998.” That this is not the case seems to be something that AR5 concedes a little later in the report when it that none of the warming trends they quote are statistically significant!

Referenced And Dismissed

Consider AR5’s summary: “It is virtually certain that global near surface temperatures have increased. Globally averaged near-surface combined land and ocean temperatures, according to several independent analyses, are consistent in exhibiting warming since 1901, much of which has occurred since 1979.”

Nobody doubts that the world has warmed since 1901. But why choose 1901, and what warming is natural and what is anthropogenic? As we have seen the last comment is wrong.

AR5 says: “Super-imposed upon the long-term changes are short-term climatic variations, so warming is not monotonic and trend estimates at decadal or shorter timescales tend to be dominated by short-term variations.”

So since 1979 we have has about 16 years of warming and 16 years of temperature standstill. Which is the short-term natural variation? The warming or the standstill?

AR5 says: “A rise in global average surface temperatures is the best-known indicator of climate change. Although each year and even decade is not always warmer than the last, global surface temperatures have warmed substantially since 1900.” Nobody, of whatever “skeptical” persuasion would disagree with that.

I can’t help but conclude that the pages of the GWPF contain a better analysis than is present in AR5, which is a mess written from a point of view that wants to reference the recent standstill in global temperatures but not impartially consider its implications.

The unacknowledged (in AR5) problem of the global temperature standstill of the past 16 years is well shown in its fig 1.4, which is seen at the head of this article. Click on the image to enlarge. It shows the actual global temperature vs projections made by previous IPCC reports. It is obvious that none of the IPCC projections were any good. The inclusion of the 2012 data, which I hope will be in the 2013 report, will make the comparison between real and predicted effects appear ever starker.

In summary, the global temperature of the past 16 years is a real effect that in any realistic and thorough analysis of the scientific literature is seen to be a significant problem for climate science, indeed it may currently be the biggest problem in climate science. To have it swept under the carpet with a selective use of data and reference material supported by cherry-picked data and timescales is not going to advance its understanding, and is also a disservice to science.