Dry hydroclimates in the early Eocene hothouse world

Extreme global warming events, such as that one expected for the shared socio-economic pathway (SSP) 8.5 in upcoming centuries, induce significant hydrological cycle changes characterized mainly by wet-wetter (wet-becomes-wetter) hydroclimates. However, hydroclimate changes of dry areas associated with increased temperatures are poorly understood and the occurrence of dry-drier (dry-becomes-drier) or dry-wetter (dry-becomes-wetter) conditions remains elusive. Early Eocene hothouse climates offer alternatives to assess the response of dry regions to global warming, which allows to better understand hydroclimate variability drivers in geological timescales and likely improve predictions about hydrological cycle variability under an extreme SSP 8.5-like global warming state. Here, we study the proto-Mediterranean Contessa Road (Italy) section, which contains records of a series of early Eocene carbon cycle perturbations. We used geochemical and rock magnetic data to reconstruct proto-Mediterranean hydroclimate variability, and found that orbital forcing and global warming controlled the hydrological cycle. Precession-driven insolation changes led to generation of dry/wet cycles, which occurred over superimposed aridification trends caused by short-lived (~200 kyr) carbon cycle perturbations and long-term (~6 Ma) global warming. Short-lived events caused hydroclimate perturbations that took ~24-27 kyr to recover from peak to pre-event conditions. These observations suggest that anthropogenic global warming can cause widespread aridification with impacts that exceed societally relevant timescales.