A proxy-model comparison for mid-Pliocene warm period hydroclimate in the Southwestern US

Abstract

Hydroclimate proxy reconstructions and paleoclimate models of the mid-Pliocene warm period provide insight into the forcings and feedbacks that impacted regional hydroclimate in a world moderately warmer than present. However, in the Southwestern United States, there is discord between proxies and climate models: proxy data have been interpreted to indicate much wetter conditions, while the most recent generation of mid-Pliocene warm period climate models simulates drying. We use a water and energy balance framework to directly compare paleoclimate model output to a refined compilation of proxies recording the presence and areal extent of mid-Pliocene lakes. Within this framework, we quantify uncertainties in the proxy system model parameters and in the interpretation of available proxy records. We find that despite these significant uncertainties, most paleoclimate models simulate a regional balance between precipitation and evaporative demand that could not have sustained the extent of recorded lakes from this time. Moreover, the extensive lakes included as boundary conditions in mid-Pliocene warm period climate models are inconsistent with the regional climate simulated by those same models. This study identifies and quantifies the remaining unknowns in our picture of regional mid-Pliocene warm period hydroclimate, with implications for analyses of climate dynamics during this time.