Sir, – In an unattributed article (Home News, February 16th) on proceedings at the American Association for the Advancement of Science (AAAS), your journalist reports: “More evidence is needed...to prove that our warming climate is being caused by human activity”. It is unclear from the content of the report as to whether this is a view expressed by the AAAS itself, one of the participants in the proceedings, or an opinion held by your correspondent.
The first two of these possibilities seem remote to say the least. The Intergovernmental Panel on Climate Change (IPCC) stated in its 2007 Fourth Assessment Report (AR4) that: “[S]ince 1750, it is extremely likely (greater than 95 per cent probability) that humans have exerted a substantial warming influence on climate” (IPCC AR4 Working Group 1 Report, p131).
The IPCC was established in 1988 specifically to review and assess the best available international scientific knowledge on climate change. The vast majority of the international scientific community accepts its conclusions as a robust and fair summary of the global state of scientific knowledge on the causes, effects and implications of climate change.
Credible calls for more evidence to fully establish human interference with the climate system are almost unheard of from within the international scientific community since 2007.
Even in terms of the attribution of particular extreme weather events to human causes, the science is becoming more robust and more precise as research has proceeded since 2007. Some of this research was presented at the AAAS last week, as your correspondent reported.
However, s/he did not refer to the AAAS’s own press release on this topic, which contains the following sentence: “Researchers at the AAAS Annual Meeting said that wild weather events like Superstorm Sandy and the severe Texas drought are the new normal in North America, as human-driven climate change has made these events more intense and more frequent”.
Science is based on scepticism. But that does not mean we have to wait forever before establishing a sufficient basis for remedial action against climate change, as many residents of New York, New Jersey and Texas are now increasingly inclined to vouch. – Yours, etc,
The wording of the report unfortunately does not make clear what I intended to say. I had sought to clarify whether it was correct to say any specific storm such as Sandy was caused directly by climate change as a result of human activity. I asked the scientists at the briefing if they would confirm this, but they cautioned against making such a claim. While it is clear and unambiguous that the incidence of severe storms has risen markedly, it was not possible to connect a specific storm event with human activity. –