A rather bizarre paper has been published in Scientific Reports (yes, that Scientific Reports) claiming that [an] earth system model shows self-sustained melting of permafrost even if all man-made GHG emissions stop in 2020. One immediate problem is that the name of the earth system model, which I won’t repeat, is a racial slur.
The paper claims that whatever we do, we’re now past a point of no return for global warming. It received quite a lot of media coverage, which I won’t link to, but there was a good response in the Independent – by Daisy Dunne – which includes a quote from Richard Betts:
Having talked to various colleagues, we don’t think there’s any credibility in the model.
What’s very odd is that you just need to look at the figures in the paper to see numerous problems. The paper considers two scenarios; an immediate cessation of emissions, and one where they reduce to zero by 2100. In both cases, the model suggests that atmospheric CO2 concentrations will reduce to 300ppm by 2200. This well below what is now regarded as likely; even if we stopped emitting now, atmospheric CO2 would probably not drop below 350ppm for many generations. The latter scenario also shows atmospheric CO2 starting to drop before emissions get to zero, which is also not consistent with our current understanding.
The paper also suggests that warming continues even though atmospheric CO2 concentrations are dropping. This is supposedly due to surface albedo changes, increasing atmospheric water vapour, and emission of carbon for melting permafrost. The surface albedo change is apparently much larger than other estimates, water vapour is a feedback, not a forcing, and cumulative carbon release from permafrost is (according to their paper) 175 GtC by 2500. This is roughly equivalent to what we’re likely to emit over the next 15-20 years, but over the next ~500 years. Not negligible, but not really enough to lead to the level of warming their model suggests.
For some reason, their model also suggests that the CO2 forcing will continue to increase, even if atmospheric CO2 drops back down to ~300ppm, which makes little sense.
My main point, which I’ve taken a while to get to, is that there are a number of obvious issues with what is presented in this paper that anyone who is working in this field should notice. It’s hard to see how anyone who has developed an earth system model wouldn’t notice these obvious problems, and it’s particularly difficult to understand how any competent reviewer could let these pass. They’re not exactly subtle points. Scientific Reports doesn’t exactly have a great reputation, but this is pretty egregious.