Evaluating Pre-Industrial Simulations of the Hydrological Cycle Over Europe and North Africa Using Reanalysis Data and Miocene Proxy Spatial Sampling

Understanding how the Earth’s climate responds to elevated CO₂ is crucial for predicting future climate trends. The Middle Miocene (17-14.8 million years ago) saw CO₂ levels of ~400-600 ppm, similar to today, making it a valuable analog. However, Miocene palaeobotanical samples are limited and assessing how state-of-the-art climate models represent modern climate at each specific proxy site requires further investigation. To validate how the climate model CESM1.3 performs, we compared present-day reanalysis product (ERA5: 1979-2009) against Pre-Industrial (PI) simulations with differing spatial resolutions. Focusing on North Africa, Europe, and the Mediterranean, we identified the latitudes and longitudes of the Miocene proxy sites and matched them with the corresponding ERA5 grid points. At each location, we calculated the annual average surface temperature and precipitation for both ERA5 and high- and low-resolution PI simulations. We then calculated the total difference at each site (PI model value minus ERA5 observation). This allowed us to evaluate model bias at specific locations. We hypothesize that the high-resolution PI model will more accurately capture regional climate features, such as orographic precipitation and coastal climate effects, leading to reduced bias as sampled by the proxy site locations. As CO₂ levels and extreme weather events continue to rise, evaluating how well models simulate past and present climates is essential. This analysis of CESM PI simulations and Miocene proxy data can improve future climate predictions, particularly for vulnerable regions.