Thread by @bobkopp

I’ve gotten a number of questions about the Steffen et al paper on the transition into a #HothouseEarth. Some thoughts: 1/n

As a commentary, it summarizes concerns I think are broadly shared by many climate scientists: there are amplifying positive feedbacks in the climate system that could bring us into a very diffeeent climate state, and we don’t know how to quantify many of them that well yet. 2/n

It also leads to a point often discussed in the context of sea level adaptation: in face of this sort of deep uncertainty, we need to take a flexible response - thinking about what might happen, and planning contingent actions to be taken in response to different triggers. 3/n

That said, it’s important to bear in mind that it is a comment. There is no *new* science in the piece to argue that the transition to a Hothouse will be completed rapidly (indeed, they - I think accurately - label this as a millennial transition) 4/n

Nor do they present new evidence to show that we will be committed to such a transition (in the absence of active stewardship) at 2.0 C (as opposed to 1.6 C, 2.5 C, or something else) 5/n

My personal opinion - I don’t think the authors would disagree - is we are already in a world of long-term deep uncertainty (though it gets deeper the more we emit) and the necessary response is a multicentury committment to active, flexibly responsive planetary stewardship 6/n

(As an aside, developing both the science and the networks of trust needed for decision-integrated science to support flexible, adaptive planetary stewardship is a core part of the @RutgersEOAS mission) 7/n

A thorough assessment of much of the relevant science can be found in chapter 15 of vol 1 of the Fourth US National Climate Assessment, which @KHayhoe and I led science2017.globalchange.gov/chapter/15/ 9/n

So: yes, we are at risk of long-term planetary transitions; yes, active, flexible stewardship is needed; but it’s impt to recognize that the science leading to this point is not new, nor does this commentary newly quantify it, so there should be no new cause for panic 10/n

(I don’t think the authors intended to inspire panic, but the emphasis in the coverage on the #HothouseEarth transition rather than the important idea of active, flexible planetary stewardship they also discuss does tend to lead in that direction) 11/n

The #HothouseEarth is likely real, but we don’t know what will trigger it, and the transition will take centuries. The need for active, flexible planetary stewardship is real, immediate, and certain. 12/12

(BTW, if you’re looking, I seem to have skipped 8/12 in my enumeration of tweets - you can stop looking for it!)

One more thought: Most climate scientists have expertise in natural systems, and find these interesting, important, and cool; and this sort of research dominates the Steffen et al comment 13/15

And there are rapid, interesting, impt & cool interdisciplinary advances happening in the translation of climate science through economics to quantitative risk assessment, of the sort we do @impact_lab 14/15

But I would suggest that figuring out what effective institutions for planetary stewardship look like is one of the most important & desperately needed research areas (& one to which I have only a little more to bring than my cheers) 15/15