SPANC · Evolution and Variability of Climate Sensitivity and Polar Amplification during CeNozoic Warm Climates SPANC

Forecasting the magnitude of future global warming is among the great scientific challenges. Model estimates of long-term warming resulting from a doubling of the CO2 concentration relative to the pre-industrial era range between 1.5 and 4.5 °C. The large uncertainty in this Equilibrium Climate Sensitivity (ECS) may represent the difference between the melting or conservation of large continental ice sheets, and between habitable and inhabitable regions. SPANC will quantify ECS through accurate reconstructions of past climate change. Existing ECS studies largely focus on periods that were colder than present. Importantly, however, my development of a reliable method to reconstruct past CO2 concentrations now allows for estimates of past warm climates that can serve as analogs for the future. First, I will calibrate the new CO2 proxy for high CO2 levels. Uniquely, my new approach allows CO2 and temperature reconstructions to be based on the same samples, implying optimal time control. This provides the outstanding opportunity to generate high-quality coupled CO2 and temperature reconstructions for the ice-free early Eocene and the warm but glaciated middle Miocene at unprecedented resolution. This allows ECS to be calculated based on long and short-term variability in CO2 and temperature. The combination of ice-free and glaciated periods will also determine the extent to which the presence of ice governs climate response to CO2. Study locations will be carefully selected across pole-equator transects. This allows for quantification of the amplification of temperature changes towards polar regions, crucial for ice sheet extent and volume and hence global sea levels.SPANC will provide a breakthrough regarding the ECS of warm climates. It will provide crucial new constraints on the ability of climate models to correctly simulate warm climates and climate variability forced by changes in CO2 concentrations, which is vital for reliable future climate projections.