There's a lot of apparently confident talk about how current temperatures compare with those in the past, including claims of 2023 being the "hottest year ever" or at least in the last 125,000. But how do we actually know, and how much do we actually know, about historic and prehistoric temperatures? In this Climate Discussion Nexus "Backgrounder" video John Robson examines the uses, and abuses, of various temperature proxies.

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