I remember - vaguely - the good ol' dayes when I used to talk about climate. So let's consider The Conversation's Atlantic Ocean is headed for a tipping point − once melting glaciers shut down the Gulf Stream, we would see extreme climate change within decades, study shows. Not all of it of course, and don't let me fool you into thinking that I've read it. And, as ever, you should prefer RealClimate's take.Briefly, while this is a time-dependent (~300 year) simulation, the time is not intended to represent any real set of calendar years; instead we start from pre-industrial and increment freshwater, until it "tips" at ~0.6 Sv. The main novelty then is the slow-running time; previous goes at this have tended to dump in the freshwater rather more suddenly, which may have its own effects.
But what's not at all clear from The Conversation, and which only appears rather belatedly in the RC piece, is from the discussion in the paper itself: "In the CESM simulation here, AMOC tipping occurs at relatively large values of the freshwater forcing. This is due to biases in precipitation elsewhere in the models and mainly over the Indian Ocean (37). Hence, we needed to integrate the CESM to rather large values of the freshwater forcing [∼0.6 Sv, about a factor 80 times larger than the present-day melt rate of the Greenland Ice Sheet (55)] to find the AMOC tipping event" to which SR is obliged to reply "in this model, like in most models, you need to add an unrealistic amount of freshwater, because they are in the wrong part of the stability diagram compared to what observational data imply". That doesn't fill me with confidence. What, you wanted more analysis?
Refs
* Hothouse tipping elements of no return.
* Nurture: Climatologist Michael Mann wins defamation case: what it means for scientists. But "Jury awards Mann more than US$1 million — raising hopes for scientists who are attacked politically because of their work" is optimistic: the bar, at least in the States, is very high for defamation.
* Tipping Is Optional - arch of WUWT post by WE
* Eating Animals and the Virtues of Honesty - Lab-grown meat as a way out of our greatest ethical dilemma - RH
Your RC link goes to The Conversation.
ReplyDeleteI was a little sceptical when I read the RC piece mostly because to me it seems as if SR is always on the look out, with hefty doses of squinting, for the smallest hint of trends towards doom. So I ventured over to WUWT to see what Willis E had to say about it ('Tipping is Optional') I thought he made a surprisingly good case, but YMMV. If you did the same (i.e. held your nose and read some Willis E) and thought not too disparagingly about it, you could add it as another link! That would lead to most climatey people you know never speaking to you again, so perhaps you'd have second thoughts..
I hate it when I do that... fixed. I haven't been to WUWT recently, it got a bit boring. I take it you don't mean AMOC To Collapse Scam Is Back... no, you mean as you say Tipping Is Optional. So yeah, shorn of the invective, and minus the "IMPENDING TIPPING POINT CATASTROPHE IN 3782 AD!" silliness, he's saying pretty well what I am: the added water is Quite Big. Note: those links are to archives, so you won't be polluted by clicking on them :-)
ReplyDelete"Tipping Is Optional" has a problem.
ReplyDeleteI hate it when I do that... I can't edit my comment, so added as a ref.
ReplyDelete