Tropical cyclone activity enhanced by Sahara greening and reduced dust emissions during the African Humid Period

Abstract

Tropical cyclones (TCs) can have devastating socioeconomic impacts. Understanding the nature and causes of their variability is of paramount importance for society. However, historical records of TCs are too short to fully characterize such changes and paleosediment archives of Holocene TC activity are temporally and geographically sparse. Thus, it is of interest to apply physical modeling to understanding TC variability under different climate conditions. Here we investigate global TC activity during a warm climate state (mid-Holocene, 6,000 yBP) characterized by increased boreal summer insolation, a vegetated Sahara, and reduced dust emissions. We analyze a set of sensitivity experiments in which not only solar insolation changes are varied but also vegetation and dust concentrations. Our results show that the greening of the Sahara and reduced dust loadings lead to more favorable conditions for tropical cyclone development compared with the orbital forcing alone. In particular, the strengthening of the West African Monsoon induced by the Sahara greening triggers a change in atmospheric circulation that affects the entire tropics. Furthermore, whereas previous studies suggest lower TC activity despite stronger summer insolation and warmer sea surface temperature in the Northern Hemisphere, accounting for the Sahara greening and reduced dust concentrations leads instead to an increase of TC activity in both hemispheres, particularly over the Caribbean basin and East Coast of North America. Our study highlights the importance of regional changes in land cover and dust concentrations in affecting the potential intensity and genesis of past TCs and suggests that both factors may have appreciable influence on TC activity in a future warmer climate.hurricanes | mid-Holocene | dust emissions | vegetation changes | land cover changes

Dominating Roles of Ice Sheets and Insolation in Variation of Tropical Cyclone Genesis Potential Over the North Atlantic During the Last 21,000 Years

“…As low-resolution climate models have better skill in reproducing the environmental factors important to TC formation than TC-like structures themselves (e.g., Camargo, 2013), we employ a genesis potential index (GPI) as an alternate to estimate potential change in TC frequency during the last 21,000 years. Different types of GPI have been found to be useful in capturing the spatiotemporal variability of observed TC genesis (Bruyère et al, 2012;Menkes et al, 2012) (Figure 1f) and have been used in applications in both past and future climates (Camargo et al, 2009;Emanuel, 2013;Korty et al, 2012aKorty et al, , 2012bPausata et al, 2017;Yan et al, 2017). The GPI used here is defined as (Emanuel, 2010;Emanuel & Nolan, 2004;Korty et al, 2012a;Tippett et al, 2011) GPI Geophysical Research Letters…”

Contribution of sea ice albedo and insulation effects to Arctic amplification in the EC-Earth Pliocene simulation

“…The enhanced oceanic meridional heat flux into the Arctic (Koenigk et al, 2013) and the enhanced atmospheric northward latent energy transport (Graversen and Burtu, 2016) are suggested as major contributors to future Arctic warming in the EC-Earth simulation. The EC-Earth model has also been applied to understand past climates, such as changes in the Arctic climate (Muschitiello et al, 2015), African monsoons (Pausata et al, 2016;Gaetani et al, 2017), tropical cyclones (Pausata et al, 2017a) and ENSO (El Niño-Southern Oscillation) activity (Pausata et al, 2017b) during the mid-Holocene. In this study we apply the model to the mid-Pliocene climate and focus on the effects of sea ice on Arctic climate change.…”

Atlantic Hurricane response to Sahara greening and reduced dust emissions during the mid-Holocene

“…Only a handful of modeling studies investigating TC changes during the MH are currently available (Korty et al, 2012;Koh & Brierley, 2015;Pausata et al, 2017). Both Korty et al (2012) and Koh & Brierley (2015) have focused on simulations of the Paleoclimate Modelling Intercomparison Project (PMIP), which only account for the change in orbital forcing and the greenhouse gas concentrations during the MH, assuming preindustrial vegetation cover and dust concentrations (Joussaume et al, 1999;Taylor et al, 2012) (Table 1).…”

“…Hemisphere and an increase in Southern Hemisphere TC activity despite the changes in summer insolation forcing. More recently, Pausata et al (2017) used a statistical thermodynamical downscaling approach (Emanuel et al, 2006(Emanuel et al, , 2008 to generate large number of synthetic TCs and assess their changes during the MH with an enhanced vegetation cover over the Sahara and reduced airborne dust concentrations. Their results suggest a large increase in TC activity worldwide and in particular in the Atlantic Ocean in the MH climate.…”