A primary goal of paleoclimate research over several decades has been to establish the magnitude of temperature change in different regions since the Last Glacial Maximum (~23-19 thousand years ago). Data on past climates have been used to study climate processes, evaluate the accuracy of model simulations, and assess climate sensitivity to greenhouse gas forcing. During this seminar, I will present what we have been learning about glacial paleoclimate from the application of carbonate “clumped” isotope thermometry. This proxy is based on the measurement of multiply substituted isotopic variants of molecules (isotopologues). I will describe results from modern samples and glacial samples, including from the Western Tropical Pacific.