主讲：V. Ramaswamy, NOAA/Geophysical Fluid Dynamics Laboratory
Aerosols arising as a result of human-induced emissions form a key ‘driver’ in the forcing of climate. However, aerosols also pose a central uncertainty in the comprehensive understanding of anthropogenic climate change. The manner of the forced climate change is sensitive to the scattering and absorption properties of the aerosols. Using the NOAA/ GFDL global climate models, including the latest “CM4” model used in CMIP6, we investigate the radiative perturbations due to the 20th Century aerosol emissions and the resulting climate response. It is indisputable that aerosols have provided an “offset” to the warming tendency due to increases in the greenhouse gases over the 20th century. But the story on other climate aspects remains complex. Particularly, in the tropical and Asian regions which have experienced substantial changes in aerosols over the past fifty years, simulations reveal a marked sensitivity of the climate variables (e.g., regional surface temperature, precipitation, and Walker and Hadley circulations) to the evolution of the aerosols. Significant uncertainties remain concerning the aerosol species relative to the well-mixed greenhouse gases which affect inferences about the net anthropogenic forcing, detection-attribution of climate change, and climate projections. Compounding the problem is the lack of or incomplete knowledge of the various species of aerosols (e.g., scattering and absorbing aerosols), microphysical interactions of aerosols with clouds, and the state of preindustrial aerosols. The 21st Century predictions will have to not only account for the above-mentioned aspects quantitatively, but also the nexus of aerosols with pollution, air quality, and health.