Impact of an acceleration of ice sheet melting on monsoon systems

Abstract

Abstract. The study of past climates demonstrated the occurrence of Heinrich events during which major ice discharges occurred at the polar ice sheet, leading to significant additional sea level rise. Heinrich events strongly influenced the oceanic circulation and global climate. However, standard climate change scenarios (Representative Concentration Pathways or RCPs) do not consider such potential rapid ice-sheet collapse; RCPs only consider the dynamics evolution of greenhouse gases emissions. We carried out water-hosing simulations using the Institute Pierre Simon Laplace global Climate Model (IPSL-CM5A) to simulate a rapid melting of the Greenland and Antarctic ice-sheets, equivalent to +1 and +3 m additional sea level rise. Freshwater inputs were added to the standard RCP8.5 emission scenario over the 21st century. The melting of the Greenland and Antarctic ice sheets have differentiated impacts. In the Antarctic, the fresh water input is diluted by the circumpolar current and its global impact is moderate. Conversely, a release of freshwater in the North Atlantic slows down the Atlantic meridional overturning circulation. This slowdown leads to changes in winds, inter-hemispheric temperature and pressure gradients, resulting in a southward shift of the tropical rain belt over the Atlantic and Eastern Pacific region. The American and African monsoons are strongly affected and shift to the south. The North American monsoon occurs later, while the South American monsoon starts earlier. The North African monsoon is drier during boreal summer while the South African monsoon intensifies during austral summer. Simulated changes were not significant for the Asian and Australian monsoons.