The emergence of new proxies enables us to address fundamental questions about Earth’s climate evolution. We can apply novel methods to help visualize the past, and compare observations with theoretical predictions from computer models to probe how atmospheric and oceanic dynamics respond to changing climate forcing. I will discuss applications of a new geothermometer to study the climate of the last ice age. This geothermometer is based on the abundance of 13C-18O bonds in carbonates, termed “clumped isotope” thermometry. Specifically we will look at new results from studies that examine how terrestrial hydrology in the Western United States and central China have evolved over the past ~20,000 years.