It appears that the action on Wednesday afternoon was where I was not: in the session on tipping points. Chris Jones of the Met Office’s Hadley Centre presented some studies of the Amazon (abstract in pdf) that have caused a big media stir. The studies suggest that a) there is a threshold level of warming beyond which much of the Amazon forest is committed to die back (probably being replaced by savanna) and b) that for significant parts of the forest that threshold is alarmingly low. Indeed it is quite possibly either unavoidable in the near future or already dwindling in the rear-view mirror. As I understand it from people who saw the presentation, models in which all the warming already in the pipeline (ie with no further emissions) is realised leave the forests pretty much committed to some dieback, and modest further warming seals the deal. I wasn’t able to check that with Jones himself, but it seems to fit with what he and his colleagues write:
We present results to show a possible climate threshold beyond which some dieback is committed and this commitment rises dramatically for global temperature rise above 2 degrees C, a threshold often used by policy makers in their definition of dangerous climate change. Any subsequent recovery is on such a long timescale as to make the dieback effectively irreversible on any pragmatic level.
Here’s the coverage from the Times and here’s some from The Guardian. Worth noting that it’s a single study, that there are error bars to consider and that people have in the past suggested that the Amazon is often more vulnerable in the Hadley Centre model than in most others. But still very worrying; all the more so if it were to be spun as a counsel of despair on efforts to stop deforestation on the basis that there’s no point preserving a forest that’s already doomed.
I’ll see if I can find Chris Jones, or some Brazilians, or both to talk about this with on Thursday.