The future of regional climate in the southwestern U.S. remains uncertain, as climate models struggle to predict how precipitation and temperature will respond to increasing atmospheric CO₂ and accompanying warmth. While models largely predict that dry areas will become even drier under global warming, geologic records in the southwestern U.S. show that the region was wetter than it is today during past periods of warmth. To better prepare for future climatic changes, it’s important to understand how the region behaved in the past, including whether the region is more sensitive to regional or global changes. To investigate how the southwestern U.S. may have responded to global temperature change during a period of prolonged warmth followed by progressive cooling, we use an isotopic proxy of soil carbonates that is directly controlled by temperature at the time of carbonate formation. We also use stable isotope proxies, sensitive to precipitation and productivity changes, to interpret precipitation and moisture changes over the same period. Our record shows that temperature in the southwestern U.S. largely followed the patterns of global temperature change and that regional precipitation patterns experienced a major shift away from wintertime precipitation and towards summertime precipitation as global climate cooled and dried.