Future Changes in Active and Inactive Atlantic Hurricane Seasons in the Energy Exascale Earth System Model

Abstract

North Atlantic tropical cyclones (TCs) have considerable interannual variability, with La Niña and the positive phase of the Atlantic Meridional Mode (AMM) tending to drive active hurricane seasons, and El Niño and the negative AMM often driving inactive seasons. Here, we analyze how active and inactive Atlantic hurricane seasons may change in the future using the high resolution Energy Exascale Earth System Model (E3SM). We performed atmosphere‐only simulations forced by sea‐surface temperature patterns characteristic of La Niña and the positive AMM jointly, and El Niño and the negative AMM jointly, in historical and future climates. Projected Atlantic TCs become more frequent in the future by approximately 34% during El Niño and negative AMM and by 66% during La Niña and positive AMM, with a significant increase in the portion of intense TCs. Warmer SSTs increase TC potential intensity, with reduced wind shear and increased mid‐tropospheric humidity further supporting TC activity.

The Influence of Climate Variability and Future Climate Change on Atlantic Hurricane Season Length

“…Furthermore, E3SM projects a substantial increase in Atlantic hurricane season length by 41 days under mean climate change with neutral ENSO and AMM, and by 27 days under mean climate change paired with positive AMM and La Niña conditions. These future increases in Atlantic hurricane season length, taken together with substantial future increases projected in Atlantic TC number and intensity under both neutral AMM and ENSO and co‐occurring positive AMM and La Niña (Sena et al., 2022), indicate the potential for exacerbated Atlantic TC impacts in the future arising from more frequent and more intense TCs occurring over an extended hurricane season.…”

“…In addition to the historical observations, we analyzed 10‐member ensembles of TC‐permitting (∼0.38° resolution) atmosphere‐only E3SM simulations (Sena et al., 2022). The simulations include a (1) historical control, which represents the historical climate with seasonally varying SST (i.e., under neutral AMM and ENSO conditions), (2) historical “active” Atlantic hurricane season simulation, which is forced with the combined tropical Atlantic and Pacific SST patterns that tend to drive active Atlantic hurricane seasons (i.e., the positive phase of the AMM with La Niña), (3) historical “inactive” Atlantic hurricane season simulation, which is forced with the combined tropical Atlantic and Pacific SST patterns that tend to drive inactive Atlantic hurricane seasons (i.e., the negative phase of the AMM with El Niño), and (4–6) the same simulations as (1–3) but under future greenhouse gases, aerosol, and SST conditions.…”

“…We investigated how tropical Atlantic and Pacific SST variability can influence hurricane season length in the historical record by performing a novel investigation of the factors that drive hurricane season start and end individually. In addition, we analyzed future changes in Atlantic hurricane season length in ensembles of TC‐permitting E3SM simulations forced with concurrent patterns of ENSO and AMM in historical and future climates (Sena et al., 2022).…”

“…Notably, it is necessary to consider the combination of tropical Atlantic and Pacific SST conditions together, as favorable AMM (positive phase) and ENSO (La Niña) patterns together act constructively to produce even greater Atlantic TC activity than either of the patterns alone, whereas AMM and ENSO patterns that individually oppose each other in their influence on Atlantic TCs can compensate when co‐occurring to produce near‐average Atlantic hurricane seasons (Klotzbach, 2011b; Patricola et al., 2014). Simulations using the Energy Exascale Earth System Model (E3SM; Golaz et al., 2022) project that when the most favorable AMM and ENSO combination is paired with future climate change, Atlantic hurricane activity increases substantially, indicating that the most active Atlantic hurricane seasons in the historical record could become exacerbated by climate change (Sena et al., 2022).…”

Projected Increase in Extremely Active Atlantic Hurricane Seasons

“…Given that seasonal TC activity in the North Atlantic is largely modulated by the difference in SSTAs between tropical Atlantic and Paci c basins 45 , a projected increase in the interannual variability of ENSO 51 and tropical North Atlantic SST 52 suggests an increase in the interannual variability of the future interbasin SST difference and hence North Atlantic TC activity. A recent work 53 used idealized SST-forced model experiments to investigate how extremes in seasonal TC activity may change due to the joint effects of ENSO and the Atlantic Meridional Mode and found that extremely active seasons becomes more common under anthropogenic effects, with greater TC number and a shift to stronger TCs. While these results are based on a single SST-forced model, without air-sea feedbacks, it highlights the importance of considering changes in the mean and interannual climate variability in uencing TC activity.…”