The Aerosol-Monsoon Climate System of Asia: Changes and Vulnerability

Worsening air pollution and increasing frequency of severe floods and droughts in Asia, are two of the most important present and future threats affecting the fresh water supply and public health of more than 60% of the world population.   As a result of active research in the last decade, there is now an increasing body of evidence indicating that monsoon rainfall and aerosols – the tiny particles suspended in the atmosphere during air pollution, are strongly interacting, playing key roles in the evolution of the present and future climates of Asia.  In this talk, I will review recent advances on our understanding of the variability of the coupled aerosol-monsoon climate system, and interactions among aerosol emissions, transport and atmospheric dynamics in South Asia and East.  Possible interaction pathways may include local effects through aerosol impacts on atmospheric radiation, and microphysics of clouds, as well as non-local effects arising from aerosol emission, transport, and feedback processes involving changes in rainfall, moisture, winds, thermal contrast, and heat sources and sink re-distributions in the atmosphere-ocean-land monsoon system.  These interactions take place over a wide range of temporal scales from hourly to multi-decadal, and spatial scales from 1-10⁵ km.   

In an assessment of possible impacts on the Asian monsoon by aerosols compared to those by greenhouse gas (GHG) warming,  we found that, on the large-scale, GHG warming alone can have both enhancing and limiting effects through differential heating of the land and ocean for monsoon precipitation and circulation, and that overall aerosols tend to suppress monsoon precipitation.  Changes in regional monsoon precipitation are manifested as the residual effects of these two dominant, but opposing climate change agents.   However, on a more local scale, aerosol may amplify GHG warming effects.  Results will be presented showing that pre-monsoon accumulation of deep layer of absorbing aerosols (dust and black carbon) trapped by local topography may interact with monsoon dynamics, can exacerbate global warming effects via dynamical feedback processes, leading to re-distribution of monsoon rainfall, and increased vulnerability to climate change over specific regions in Asia.   Examples included accelerated melting of high mountain glacier and snowpack, bursting of glacier lakes, disastrous flooding and mudslides, uprooting the livelihood of millions in the Himalayan foothills, the Sichuan Basin and other mountainous Asian monsoon regions with dense populations.