Plain Language Summary
Future changes in global-mean temperatures have substantial implications for climate-related risks, and global-mean temperatures will continue to increase in response to carbon emissions (a property known as climate sensitivity). In addition to long-term, human-driven warming, the global surface temperature also exhibits short-term swings due to natural climate variability. Recently, climate model experiments have shown some evidence of a linear relationship between climate sensitivity and climate variability, with potential applications for climate model development and future predictions. We show that this relationship holds when applied to paleoclimate data from the Common Era (850-1999) and use the reconstructed temperature record over this period to estimate climate sensitivity. Our analysis considers a period (~1000 years) that is much longer than what has been used in prior studies (~100 years) and thus paints a fuller picture of past temperature variability. We show that interannual and decadal fluctuations in climate could offer a novel technique for assessing the Earth’s sensitivity to external forcing. Our results are consistent with other lines of evidence, increasing confidence in our approach. We hope our findings add value to the existing collection of climate sensitivity estimates and encourage future use of paleoclimate data to verify proposed constraints on climate quantities.