Earth's climate sensitivity – defined as the temperature increase for a doubling of pCO2 – and the mechanisms responsible for amplification of high latitude warming remain controversial. The latest Paleocene/earliest Eocene (LPEE; 57-55 million years ago) is a time when pCO2 peaked between 1400 and 4000 ppm, which allows us to evaluate the climatic response to high pCO2. Here, we present a reconstruction of continental temperatures and oxygen isotope compositions of precipitation – reflective of specific humidity – based on clumped and oxygen isotope analysis of pedogenic siderites. We show that continental mean annual temperature reached 41 °C in the equatorial tropics, and summer temperatures reached 23 °C in the Arctic. The oxygen isotope compositions of precipitation reveal that compared to the present-day the hot LPEE climate was characterized by an increase in specific humidity and the average residence time of atmospheric moisture and by a decrease in the subtropical-to-polar specific humidity gradient. The global increase in specific humidity reflects the fact that atmospheric vapor content is more sensitive to changes in pCO2 than evaporation and precipitation, resulting in an increase in the residence time of moisture in the atmosphere. Pedogenic siderite data from other super-greenhouse periods support the evidence that the spatial patterns of specific humidity and warmth are related providing new means to evaluate Earth's climate sensitivity.
Cenozoic global TEX86-derived sea surface temperature (SST) compilation from all published marine TEX86 records and new data measured in this study (ODP/DSDP Sites 516, 588, 667, 704, 730, 754, 1146 and 1263). This table contains all GDGT measurements, calculated indices, SSTs and SST gradients.