Yes, the post you've all been waiting for. Before reading my take you should of course read
RealClimate, but I suspect like me you'll be a touch disappointed, because that post is bland. I shall quote from it:
The summaries and FAQ are good, and the ClimateNexus briefing is worth reading too. The basic picture is utterly unsurprising, but the real interest in the NCA is the detailed work on vulnerabilities and sectorial impacts in 10 specific regions of the US. The FAQ is also unsurprising if you know this stuff, but does include a ref to our
ice-age myth stuff, which is nice.
You'll also be disappointed - perhaps shocked - to discover that I haven't read the whole thing. Instead I looked for something to latch onto, and found this pic, which is from... well, OK, let me tell you a story. The pic is a version of something I
saw in a Twit, and thought, hmm yes very interesting but where do I find the data, analysis, discussion? So I looked through
the report chapters (sorry, the report format appears to be shitty javascript written by script kiddies, making it impossible to link directly to the chapter overview) and failed to guess which of the chapters it might be from. Fortunately, Google is more useful than NCA, and
site:https://nca2018.globalchange.gov/ "annual damages" found me what I wanted:
Chapter 29, Mitigation. Of course. As an aside, the report to me appears to be waaay behind the IPCC reports in terms of sourcing the summaries back to the chapters. Anyway, that bit of Chapter 29 sources itself to
Multi-Model Framework for Quantitative Sectoral Impacts Analysis: A Technical Report for the Fourth National Climate Assessment, and so I looked at that.
As you'll see, the three biggest impacts on that graph, as measured by dollars, are: Labour, Extreme Temperature Mortality, and Coastal Property. To a first approximation, each of those are a quarter, and everything else is another quarter. I was going to do Labour, but the first one along was ETM, so I thought I'd do that instead. Note first that
The study also only considers deaths related to extreme temperatures, though extreme heat will... do other stuff too; so this isn't complete.
$141B/yr is a Big Number, but we all known that Big Numbers without some kind of context or referent are meaningless. Let's try to put it into place. As the report says,
This analysis estimates the number of deaths over the course of the 21st century attributable to extreme temperatures in 49 cities in the contiguous U.S., which account for approximately one third of the national population. So that's a bit funky: you might at least expect them to multiply it by three or something. That number - by 2090 - represents 9,300 deaths/yr which is ~$15M/life by a quick in-my-head calc; and looking at footnote 142 I see I'm right. Soooo... how might we assess that? Imagine (I do this just to wind you up, you understand) we were talking not about people, but about industrial plant. Then we'd want to compare those 9,300 people to the replacement rate; which is currently abut 1%, of about 300M, which is to say the population is growing by 3M/yr. Against which 9,300 is about 0.3%, if I have my maths right. Scaling that, we might expect a similar number from the GDP figures: $141B is large, but the US GDP in 2018 was ~$20Tr, of which $141B is about 0.7%, which is close enough, as I haven't been very careful about what year I'm looking at.
The next interesting thing to consider is
Mortality from extremely hot days decreased more than 50% under both RCP8.5 and RCP4.5 in 2050 and 2090 when the human health response to extreme temperatures was evaluated using Dallas’ threshold for extreme heat (in all cities with thresholds initially cooler than Dallas), as a sensitivity analysis to consider the effect of adaptation. Which is a good place to remind ourselves that, for simplicity, the initial figures are with no adaption, a not very plausible scenario. Unfortunately they don't really explore Dallas-world in depth, so it is nothing but a sensitivity analysis; but if you think $141B is large then you presumably think $70.5B is also large, and so should be very interested in exploring an effect that large.
If you follow the spiral of bubbles down to near the centre you'll eventually come to "shellfish" at $23M/yr. Now I quite like shellfish, some of my best friends are shellfish, but compared to the uncertainty in $141B, 23M is less than a rounding error, so why they bothered - other than pressure from the shellfish associations - I really don't know.
I should also point out that these are RCP8.5, which you can call too high if you like, and can consider RCP4.5 if you prefer, in which case you get to cut the numbers in half.
Update: I didn't explicitly note it here, but their estimate of the (small) changes due to winter mortality don't look plausible to me, especially in the face of stuff like
Excess winter deaths in England and Wales highest since 1976 from the Graun.
Refs
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The management apologise for any inconvenience - aka Estimating economic damage from climate change in the United States by Solomon Hsiang et al., Science 30 Jun 2017.
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10% of GDP? - ATTP