Yesterday scientists from the Universities of Exeter and Oxford together with University College London, announced that climate change is not as bad as previously thought due to modelling errors. In a paper published in the journal Nature Geoscience, the scientists concluded that global climate models used in the 2013 report from the Intergovernmental Panel on Climate Change (IPCC) tend to overestimate the extent of warming that has already occurred. (The paper can be found here, with supplementary data here.)

“An important uncertainty within this study is the specification of the attributable warming in the present-day climate state.”

The researchers used three approaches to evaluate the outstanding ‘carbon budget’ (the total amount of CO2 emissions compatible with a given global average warming) for 1.5°C. In all cases the level of emissions and warming to date were taken into account, and they found that the amount of carbon that humanity can emit from 2015 onwards while holding temperatures below 1.5°C is nearly three times greater than estimated by the IPCC – or even more if there is aggressive action on other greenhouse gases beyond carbon dioxide.

“Previous estimates of the remaining 1.5°C carbon budget based on the IPCC 5th Assessment were around four times lower, so this is very good news for the achievability of the Paris targets,”
Professor Pierre Friedlingstein, University of Exeter.

The IPCC models suggest that global temperatures should be 1.3°C above mid-19th century levels, whereas recent data suggest the increase is only 0.9-1.0°C.

“We haven’t seen that rapid acceleration in warming after 2000 that we see in the models. We haven’t seen that in the observations,”
Myles Allen, professor of geosystem science at the University of Oxford quoted in The Times.

The same article explains that the original forecasts were based on twelve separate computer models made by universities and government institutes around the world, which were compiled a decade ago, so it is perhaps unsurprising that there is a degree of divergence between the models and observable data.

Paul Homewood writing on the blog Not A Lot of People Know That makes the following comments:

  • We have known for several years that the climate models have been running far too hot. This rather belated admission is welcome, but a cynic would wonder why it was not made before Paris.
  • I suspect part of the motivation is to keep Paris on track. Most observers, including even James Hansen, have realised that it was not worth the paper it was written on. This new study is designed to restore the belief that the original climate targets can be achieved, via Paris and beyond.
  • Although they talk of the difference between 0.9°C and 1.3°C, the significance is much greater. Making the reasonable assumption that a significant part of the warming since the mid 19thC is natural, this means that any AGW signal is much less than previously thought.
  • Given that that they now admit they have got it so wrong, why should we be expected to have any faith at all in the models?
  • Finally, we must remember that temperatures since 2000 have been artificially raised by the recent record El Nino, and the ongoing warm phase of the AMO.

It is encouraging that this study is highlighting the disparity between the IPCC’s climate models, and observable data. As I have noted previously, it is difficult to reconcile the IPCC’s conclusions about anthropogenic climate change, and the fact that the data do not support the predictions of the climate models.

“For the period from 1998 to 2012, 111 of the 114 available climate-model simulations show a surface warming trend larger than the observations. There is medium confidence [66-100%] that this difference between models and observations is to a substantial degree caused by natural internal climate variability, which sometimes enhances and sometimes counteracts the long-term externally forced warming trend….”
IPCC 2014 Climate Change Report.

While the authors of the new study approached their work in terms of demonstrating that the Paris climate accord targets are achievable, this should not be taken as a signal to progress with aggressive de-carbonisation policies. The counter-argument to current climate change orthodoxy is that rising levels of atmospheric CO2 are the result of, and not the cause of, rises in global temperature (the data are presented and explained here with reference to the Vostok ice core samples).

If this alternative hypothesis is correct, the difference between the climate models and the observable data would be explained, meaning that expensive de-carbonisation schemes are un-necessary and will not impact climate change.

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