Great to see the long record finally becoming more robust. https://twitter.com/MichaelEMann/status/1304419677372907521

Has been a long-standing interest. Estimates have existed for 15+ years, but crude ones based on ordinary measures of the wrong thing (stable oxygen isotope ratios from deep-water benthic foraminifera). This is still that, but with much better coverage.

http://gergs.net/all_palaeotemps/

That old graph of mine actually got a cite in a proper peer-review-published version that attracted some attention, a while back. Amused, was: https://twitter.com/ASchmittner/status/1074836572833337344?s=20

The new paper is here ($$s): https://science.sciencemag.org/content/369/6509/1383

The problem with δ¹⁸O measured on the sub-fossil shells of bottom-dwelling deep-ocean forams (little critters…) is the best that can measure is deep ocean temperature, which is *much* colder than surface temperature … and even that is obfuscated by the background ocean ¹⁸O…

But it's a measure, and it's possible to extract an approximate estimate of average global surface temperature, which plotted.

(Background ¹⁸O mostly depends on how much water is locked up in ice, globally, and we know that, roughly … and before about 5 My ago there was none.)

Modern humans, btw, have existed for about 250,000 years; agricultural societies for about 10,000 years; industrial societies for about 200 years, and social media for about 30 years (hi, Usenet). You're welcome.