Have our climate models been wrong? This is the title of a new episode of the BBC World Service’s “The Inquiry”, available here on BBC sounds. It’s about the emphasis on RCP 8.5, often misleadingly referred to as “business as usual”.

After introducing the topic via James Hansen’s call to action in 1988, and the formation of the IPCC, the presenter says that some scientists are saying too much emphasis has been put on the worst case scenarios.

Four expert witnesses are presented. The first is Chelsea Harvey, a reporter for E&E News, who introduces the RCP scenarios, explaining that RCP 8.5 is a worst case scenario based on rapid expansion of coal use. She says it’s human nature to be attracted to the worst case scenario.

Expert number two is Justin Ritchie, who says he started to question why RCP 8.5 was getting so much attention while he was doing his PhD.

Next up is Roger Pielke Jr, who says the proliferation of use of RCP 8.5 is a prime example of the misuse of science.

We got off track when we started treating scenarios not as scenarios of the future but as predictions or projections of the future. When academics such as myself publish papers and university press offices put out press releases, you can be guaranteed that the most notable newsy studies will be those that employ RCP 8.5, and somewhere – I don’t think any of this is conscious, but somewhere along the way we take a scenario that is highly improbable, highly unlikely, and it goes through the process and shows up on the BBC or the front page of the New York Times as “where we’re headed” stripped of all the context and details, because it is a complicated topic, and if we repeat that hundreds of times, every year for the last decade, we get a picture of climate change that is not necessarily in conformance to what the broader literature actually says.

The analogy I often use in these situations was the decision to go to war in Iraq. In the short term there was a lot of fear generated by raising concerns of weapons of mass destruction and in fact it did lead to short term action with long term consequences – the invasion of Iraq. Later when it was discovered that the intelligence wasn’t quite sound, and may have had some political influence, there was a lot of lost credibility among the intelligence community, but also those politicians and policy makers who had pushed very hard for action based on the science. We shouldn’t evaluate science buy the worthiness of the cause, because that doesn’t lead to good decision making. The continued use of RCP 8.5, and presenting it as business as usual, gives ample fodder for those who are opposed to action on climate change to criticise the scientific community, and they will be in real respects standing on solid ground when they do so.

Does he have debates with scientists who say, can you stop talking this down?

Oh absolutely, all the time. It is interesting that for some people, they say, well climate change is far too important to air the questions, uncertainties, course corrections, going on within science, and I have exactly the opposite view: climate change is far too important not to have those discussions. Because science is messy, it’s course correcting, which is one of its strengths, and climate change is one of the critical challenges of this generation, and if we don’t have the science right I can’t think we’re ever going to get the policy right.

Finally we hear from Richard Betts, who attempts to defend the continued use of RCP 8.5.

The way you’re framing the question is, have we been looking at the wrong scenarios, and I don’t think so, because we need to account for a whole range of future possibilities, and it’s very important to guard against overconfidence, and thinking that we can predict the future perfectly, when we can’t.

Richard tries to claim that even with lower emissions we could still get to RCP8.5’s higher CO2 concentrations. Because when you mow your lawn, it decomposes and the carbon dioxide goes back into the atmosphere. Or perhaps the ocean might somehow stop absorbing carbon dioxide. The programme didn’t mention the almost 12 million euros of grant funding, mostly from the EU, that Richard and colleagues received specifically to study “High End Climate Impacts and Extremes” (HELIX).

The narrator ends with this summary:

Have our climate models been wrong? All our expert witnesses say treating the most severe trajectory, RCP 8.5, as the “business as usual” baseline scenario was wrong. That placed us in the spotlight and as a result, our climate modelling has put too much emphasis on an unlikely scenario. The truth is, there are many paths we could take into the future. None of them look easy, and some look horrendous.

Update:

HT Bishop Hill. Another possible explanation for the rather desperate attempt to keep RCP 8.5 alive is that the Met Office’s UK predictions, UKCP 18, make use of RCP 8.5, see documents here and here. Excerpts: