"Reliable" is obviously a spectrum, and nothing beats a thermometer. However, there are multiple independent reconstructions of temperatures over the past 2000

"Reliable" is obviously a spectrum, and nothing beats a thermometer. However, there are multiple independent reconstructions of temperatures over the past 2000 years using a variety of proxy sources, from rings in trees to coral growth to bores in Antarctic ice [0]. They provide sufficient evidence that the IPCC thinks it's "likely" (a technical term) that temperatures are higher than anytime in the past thousand years. [0] https://en.wikipedia.org/wiki/List_of_large-scale_temperature_reconstructions_of_the_last_2,000_years https://en.wikipedia.org/wiki/List_of_large-scale_temperatur...