In this episode of Forecast, Jess tells Mike about the origins of the TEX86 temperature proxy — an index of membrane lipids produced by mesophilic archaea. The origins in the 1980s in extreme ocean environment; discovery of membrane production in a huge range of environments; brute force discovery of the index; the inevitable struggles to understand what it actually represents; an unusually active and sometimes dismissive debate about its usefulness. All proxies have issues, but Jess and her colleagues are converging on the what/when/where for TEX86’s application. For Jess, work on TEX86 (and other methods!) is leading to an improved understanding of the atmospheric dynamics, surface processes, and feedbacks governing past climate variability, particularly in the tropics.