BBC: Climate Change By The Numbers

  • Date: 04/03/15
  • Dr David Whitehouse

The BBC has just aired a documentary called “Climate Change By The Numbers” in which three statisticians tackle the thinking behind three important numbers associated with climate change – 1) the Earth’s temperature increase since 1880 which is 0.85°C, 2) the idea that scientists are 95% certain about it all, and 3) the 1 Trillion tonnes of carbon dioxide is the maximum we can safely deposit into our atmosphere.

Disappointingly the programme championed style over content. Its treatment of the so-called pause in global annual average surface temperature was misleading. It was described as controversial, although those who say it is statistically meaningless and unimportant are few if vocal, and declining as the “pause” continues. The start date given for the “pause” was incorrect as was the assertion that not all surface temperature datasets show it. The discussion about the reasons for the pause was perfunctory concentrating on the missing Arctic data theory published last year by Cowtan and Way. It was said that when their adjustment was made there was a slight warming trend. What was not said was that this trend is statistically insignificant, surely an important point in a documentary about statistics and climate change. The “pause” was dismissed as a statistical fluke and then, briefly, suggested it might not exist. Also, the “pause” was not predicted by climate scientists other than in a most general way, and with possible durations very much shorter than that currently observed.

What also annoyed me was the lack of error bars in the graphs, especially in the section about the “pause.” Too much hand-waving conjecture about temperature data can be gotten away with if error bars are not included in the data. They could have done a section on accuracy of surface temperature data and displayed the data relevant to the “pause” at that accuracy using one of their light-stick displays. It would have been a straight line. Now that would have been a talking point.

Truth By Association

The transition to section two was not smooth and involved moving the goalposts. We left section one with a 0.85 (errors?) °C global temperature increase since the 1880s. Now we were told there is 95% confidence that half of the post-1951 warming was likely due to mankind. This section got the data wrong in saying there was more post-1951 warming than before. There was no mention of the temperature climb out of the Little Ice Age.

We are told of the value of climate models run on supercomputers and how good they were with no mention that the CIMP5 ensemble does not seem to conform with the reality of the past 20 years – no matter, they worked well predicting the post-Pinatubo temperature dip! This is “good evidence that climate modeling could be reliable.” Other proof of their effectiveness was given such as Arctic ice loss, increased number of heatwaves and the warming and acidification of the oceans! Where was this programme getting its scientific data from?

In the end it came down to a graph that showed how only with the inclusion of human intervention can the post-1950 climate be explained. Natural climatic variability cannot do it alone. No mention of the fact that the model used for natural variability was a simple one that we know cannot be accurate. It omits many of the causes of climatic variability invoked to explain the post-1997 “pause.”

A lot of the programme was “truth by association” suggesting that because a certain approach worked in one instance it obviously will work in another i.e. climate change. As proof we were offered things that fitted with this viewpoint and almost nothing that didn’t.

So Climate Change By The Numbers was a disappointment and a wasted opportunity and certainly not the start of a new narrative in the debate about climate change. But, in the interests of impartiality, why not allow three sceptics a similar platform to present their view of climate data?

Also, the “pause” is clearly a major area of research and debate in climate science having been described by Nature as the biggest problem in climate science. It’s been so for years, so isn’t it about time the BBC did a proper treatment of it and not just seek comments from the usual suspects? Discussion about the “pause” is everywhere, except on the airwaves.


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