My main point is that we have "scientists" willing to put economic cost projection figures on devastating climate change: that it will "cost" x% of GDP growth going forward. These are complete and utter bollocks - no one can predict all the costs of climate disasters. 2/

But that doesn't stop these figures being quoted in the press, repeated by scientific colleagues who should honestly know better, and even Nordhaus, the leader of this area, being awarded a Nobel Prize in economics last year. 3/

Yes, these numbers are "educated estimates" or "projections" or whatever, but still, just utter nonsense. Saying that one knows that 4 degrees of warming will result in x% of GDP costs, when it will make the tropics uninhabitable is just nonsense and should be treated as such. 4/

But that raises another question: what about the human costs of climate impacts? Surely we should be able to estimate those better? I mean those are based on real science, right? Like deaths from heat, hunger, flooding, disease spread, etc? Surely these could be estimated ... 5/

with much stronger scientific accuracy? And the answer here is really interesting, because it's both yes, no, and no one is supporting this area of research enough. Yes, some pathways between impacts and health are very well known. [Thread interruption due to family morning. TBC]

[Thread resumes, three days later. We take breakfast *very* seriously in this family, apparently.] First a citation footnote to tweet 4/ (doing twitter right, yes?): the tropics becoming uninhabitable at 4 degrees (RCP 8.5) is from Mora et al 2017. 7/
https://www.nature.com/articles/nclimate3322

Second point: the thread, incomplete as it was, generated quite a bit of interesting discussion with actual experts (egads) contributing. I'll get to some of those points and respond too but I want to finish my original train of thought. Still doing twitter right. Tweet 8/

So the human costs of climate impacts can be measured and modeled quite well *in some cases*: see the Mora et al paper above for a really good example. These are cases when the link is very direct (too much heat & humidity => death). But what if the links are indirect? 9/

And that's where things get really interesting, and where we understand that social science needs to be taken seriously: climate impacts are in many cases what the Pentagon calls a "threat multiplier", meaning they can aggravate an already bad situation, or trigger a crisis. 10/

Take a climate impact of low crop yields: if it coexists with large economic inequality and poor social security, it will precipitate a large fraction of the population into dire poverty, with risks of hunger, loss of farms, ensuing political crisis/conflict. 11/

Some say this particular scenario has already played out in the Arab Spring and aftermath. If the society is more equal and has better social security and democratic function, the population may be much better protected. [Thread interruption for family morning again! sorry.] 12/

In 2014, the World Health Organization published a "Quantitative risk assessment of the effects of climate change on selected causes of death, 2030s and 2050s" which I believe is still the most comprehensive overview of the science. 13/
https://www.who.int/globalchange/publications/quantitative-risk-assessment/en/

There are good reasons to believe this report and its findings (250k additional deaths in 2050) are overoptimistic (the report itself spells these out). Chapter 11 of the IPCC Working Group 2 5th Assessment Report is another overview. 14/
https://www.ipcc.ch/report/ar5/wg2/ 

What both of these reports show, from my nonspecialist position, is that
1) there are many criss-crossing pathways between climate and health impacts;
2) the impacts accelerate greatly over the course of time and warming (4 degrees is *much* worse than 2 x 2 degrees), 15/

3) the error bars on projections are huge, especially when you start thinking about the criss-crossing of the effects: for instance bringing the risk of social breakdown, lack of economic stability, conflict, etc. 16/

So one take-home message for me is that this is real science: evidence-based, perhaps overcautious and limited in terms of what it can accurately project, but trying nevertheless to give the best understanding possible. How different from the economic picture. 17/

The second take-home message (this is the important one! 18 tweets in, definitely doing this right), is the immense importance of social protection and economic equity. Health impacts can be, at least at lower warming levels, almost entirely be alleviated by social protection.

The high end of the error bars, at a high warming levels, and taking into account worst scenarios of conflict, social and economic disruption (a place where none of these reports go, because of unpredictability) is likely to be incredibly high. 19/

Indeed, possibly as high as Roger Hallam says. No one knows, it's literally a scale of disruption beyond current evidence and predictive models. The error bars are simply too large. I still think it's worth trying to estimate, but it's not my area of direct expertise. 20/

[Shameless academic volunteering: if someone out there is interested & more qualified, I'd love to help be involved in this type of estimate.]
But what is more staggering to me is that we can DOUBLY protect future human populations from disease, harm and death. 21/

First, by drastically reducing the warming in the pipeline: keeping warming to 1.5 degrees or as close as possible. This means reducing emissions drastically right now, and getting to zero fast. 22/
https://www.ipcc.ch/sr15/ 

Second, by having decent societies: socially equitable, democratically functioning (so that groups being harmed have voice and influence), with good public health, social protection and welfare systems. Our social systems protect us. We must protect them. 23/

So this is one reason I don't believe in pure market or technical efficiency when it comes to climate change: these alone don't protect against health impacts. It's the main reason I call myself an ecosocialist openly: both parts matter. 24/

And it's a core reason I refuse to engage with doomist or defeatist "all is lost" people out here (and good lord there are many of them). Literally, simply by not giving up on each other, literally by working for each other, we can save so many lives. 25/

To put it most simply, our capacity for future survival is directly proportional to our current ability to mobilize and organize popular movements for low carbon socially equitable societies. We can save each other but only if we join together and fight like hell - now. 26/

For a more comprehensive take on this, I recommend UN special rapporteur @Alston_UNSR's report on climate change and human rights. Thanks for reading this far - maybe one day I'll be able to be pithy & concise. End/
https://www.ohchr.org/EN/NewsEvents/Pages/DisplayNews.aspx?NewsID=24735&LangID=E

PS: gah, forgot to add: our capacity to protect our environments, biodiversity, etc is also proportional to our social stability and democratic function, see all environmental justice struggles ever. I follow Bookchin 200% along this general line.