Tropical cyclones (TCs) cause extreme precipitation, floods, storm surges, and destructive winds with devastating loss of lives and property.

In this study, we simulate how the genesis conditions, frequency, intensity, and geographic range of TCs vary under a wide range of past climates. Increases in computing power has allowed an unprecedented set of fully coupled high-resolution (HR) climate simulations of past greenhouse and icehouse climates to study the dynamics and thermodynamics that govern the characteristics of TCs in both atmosphere and ocean under altered climate states. We target well-studied paleoclimate intervals in the IPCC assessments: hothouse (early Eocene climatic optimum EECO, ~50 Myrs ago, with CO₂ 840 and 1680 ppm), warmhouse (Mid-Pliocene warm period MPWP, ~3.2 Myrs ago, CO₂ 400 ppm), and icehouse (LGM, ~21 kyrs ago, CO₂ 190 ppm). These results are compared to a preindustrial (PI, CO₂ 284.7 ppm) simulation and two RCP8.5 simulations to the end of this century (CO₂ 935.9 ppm at 2100). We use a configuration of the Community Earth System Model version 1.3 with a horizontal resolution of ~0.25° for the atmosphere and land models and ~0.1° for the ocean and sea-ice models. At these resolutions, the model permits tropical cyclones and ocean mesoscale eddies, and allows interactions of these synoptic and mesoscale phenomena with large-scale circulations.

The LGM has on average one CAT3 storm per year and much fewer TCs form in the North Atlantic than the PI. In the warmer climates of the MPWP, EECO, and RCP8.5 (at 2070-2100), the simulated TCs track farther poleward with more CAT3 and stronger hurricanes. The EECO simulations provide an interesting sensitivity to CO₂ concentrations. There is very large increase in CAT3 TCs at CO₂ concentration of 840 ppm, while at concentrations of 1680 ppm, the increases are much less and comparable to the MPWP and RCP8.5 simulations. As in the higher CO₂ EECO simulation, the Atlantic Main Development Region between 10-20°N becomes more hostile for TC genesis at the end of this century in the RCP8.5 simulations. Here, we will delve into contributions of local changes in wind shear, humidity, and thermodynamic properties of the environments under these altered climate states and interpretation against the available geological records.