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expert reaction to media article about a leaked draft report from the IPCC on climate warming of 1.5°C

A media article reported some of the contents of a leaked draft report from the UN’s Intergovernmental Panel on Climate Change (IPCC) about global warming of 1.5°C.


Prof. Piers Forster, Professor of Climate Change and Director of the Priestley International Centre for Climate, University of Leeds, said:

“The report is incomplete and findings can change substantially so I don’t think too much should be read into the statements.  The IPCC review process is very transparent and rigorous.  We expect to get many thousands of review comments on this draft and will need to respond to each one carefully.  Uniquely, these will all be published alongside the final report.  So come back to me this September and I’ll happily talk about the details of our work.”

Prof. David Reay, Professor of Carbon Management, University of Edinburgh, said:

“This appears to come from a leaked draft of the 1.5 degree IPCC special report.  This report has just gone to the second order draft review stage and so will change again over the coming months.  As such, it’s not really appropriate to comment on the drafts in my view – there will be plenty to say when the final report is published.”

Dr Phillip Williamson, Researcher, University of East Anglia, said:

“Commenting on the reporting of a leaked draft report is fraught with difficulties.  As the spokesperson for IPCC has said, the text almost certainly will change.  Nevertheless, if the final version of the new IPCC Special Report should, in October, reach the conclusion that there is high risk of breaching the 1.5 degrees centigrade limit by mid-century, that would be no surprise.  That is because the IPCC conclusions are drawn from the published scientific literature, based on projected emission scenarios.  The most optimistic of these, based on stringent emission reductions together with large-scale removal of carbon dioxide from the atmosphere, consider that it should, just, still be possible to limit the global end-of-the-century temperature increase to between 1.5-2.0 degrees centigrade.  But with an important proviso: that it is “allowable” to have a temperature overshoot before then, hence exceeding the limit in 30-50 years time.  That is no secret; many peer-reviewed papers have been written on that topic.  However, associated issues have not yet been explored from a policy perspective: what scale of temperature overshoot, and for how long, would be considered acceptable?  To a large extent, the answer to those questions depends on other parts of the new IPCC report, relating to the environmental, societal and economic impacts of temperature increases in the range 1.5-2.0 degrees, and the risks that thresholds involving irreversible changes and unacceptable damage might be crossed.

“With regard to what measures might be implemented to avoid such a situation, the answer is straightforward: every country needs to stop adding to the problem, by increasing the urgency of effort to reduce greenhouse gas emissions.  Indeed, to achieve a stable climate, net zero emissions are required.  That target was included in the Paris Agreement at the global level; it also needs to be the target at the national level, with each country setting an ambitious date as to when it will be achieved.”

Declared interests

Prof. Piers Forster: “I have no conflicting interests.  I am an author of the report but my response is purely in a personal capacity.”

Dr Phillip Williamson: “Williamson is employed by the UK Natural Environment Research Council, as science coordinator for the Greenhouse Gas Removal (GGR) programme, co-funded by NERC, EPSRC, ESRC and BEIS.  The GGR programme aims to assess the scientific feasibility of ‘negative emissions’ (greenhouse gas removal), without policy implications as to whether such removal should be considered either necessary or desirable.  Williamson has been invited to review the current draft of the IPCC Special Report on 1.5 degrees centigrade, but has not yet seen that document.  Williamson is a lead author on a different IPCC Special Report currently in preparation, on Oceans, Cryosphere and Climate.”

None others received.

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