Grant: Discovery Grants Program - Individual

Several climate models suggest that a future warmer climate may lead to an increase in precipitation and a potential greening of the subtropical North Africa, a reduction in airborne dust loadings, and afforestation of high latitudes. Both vegetation cover and dust were recently highlighted as major climate forcings, able to affect large-scale atmospheric circulation and its modes of variability, such as the monsoons, the El Nino-Southern Oscillation, the tropical cyclone activity and the Arctic climate. However, at present few studies are yet available on the implication of vegetation and dust changes on regional and global climate, and therefore we still lack a thorough understanding of these complex interactions that are often neglected in model simulations. Past climates, during which large changes in vegetation cover and dust emission occurred, offer a unique opportunity to improve our understanding of their role on altering climate. For example, during the African Humid Period (AHP, 11 - 5 kyrs BP), the today's hyper arid Sahara desert was transformed into a lush expanse of grass. However, the exact mechanisms involved in this transition, which may or may have not been abrupt, and the role of feedbacks from dust and vegetation changes are still open questions. Given such large vegetation and dust loading changes experienced during the AHP, this period is a good test case of our mechanistic understanding of the interplay between radiative forcing and atmospheric circulation. This period will allow to clearly detect the most important geographical regions that are able to play a larger role in affecting global climate. It will then provide opportunities to examine connections among large-scale and regional climate changes, which give rise to phenomena, such as land-sea contrast, high-latitude temperature amplification, and the waxing and waning of the monsoons. The long-term goal of this research program is to advance the science that will allow us to anticipate the climate consequences associated with aerosol-land-cover changes-climate interactions, combining methods that involve the synthesis of data, numerical climate simulations, and statistical models. The short-term objectives are 1) to systematically assess the impact of dust and vegetation cover changes in different geographical regions in affecting local and global climate (past and future) detection; 2) to investigate the associated mechanisms at play attribution through the development of ad hoc model sensitivity studies; 3) to use new paleoclimate reconstructions and model simulations to improve the interpretation of marine sediment core reconstructions of the last 20 kyrs from northwestern Africa; 4) to quantify the changes in the environmental condition in central and southern Africa to understand their potential influence on the dispersal of anatomically modern humans within the African continent.