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Climate models have not ‘exaggerated’ global warming

Factcheck: Climate models have not ‘exaggerated’ global warming , Skeptical Science,  by Zeke HausfatherThis is a re-post from Carbon Brief 6 Oct 17 A new study published in the Nature Geosciences journal this week by largely UK-based climate scientists has led to claims in the media that climate models are “wrong” and have significantly overestimated the observed warming of the planet.

Here Carbon Brief shows why such claims are a misrepresentation of the paper’s main results. In reality, the results obtained from the type of model-observation comparisons performed in the paper depend greatly on the dataset and model outputs used by the authors.

Much of the media coverage surrounding the paper, Millar et al, has focused on the idea that climate models are overestimating observed temperatures by around 0.3C, or nearly 33% of the observed warming since the late 1800s. For example, the Daily Mailreported:

According to these models, temperatures across the world should now be at least 1.3 degrees above the mid-19th century average, which is taken as a base level in such calculations. But the British report demonstrates that the rise is only between 0.9 and 1 degree.

Lead author Dr Richard Millar and his co-authors have pushed back against such media coverage, releasing a statement which says:

A number of media reports have asserted that our [study] indicates that global temperatures are not rising as fast as predicted by the Intergovernmental Panel on Climate Change (IPCC), and hence that action to reduce greenhouse gas emissions is no longer urgent. Both assertions are false. Our results are entirely in line with the IPCC’s 2013 prediction that temperatures in the 2020s would be 0.9-1.3 degrees above pre-industrial [levels].

[Carbon Brief’s guest post by Dr Millar earlier this week includes the paper’s key figures. Additionally, one of his co-authors, Prof Piers Forster, provides further reaction at the end of this article.]

Contrary to media claims, the study found that warming is consistent with the range of IPCC models, albeit a bit lower than the average of all the models.

Indeed, as Carbon Brief explains in detail below, the difference between models and observations turns out to depend largely on what climate model outputs and observational temperature series are used……….https://www.skepticalscience.com/factcheck-models-have-not-exaggerated-warming.html

October 6, 2017 - Posted by Christina Macpherson | 2 WORLD, climate change