CLIMATE-CONVECTION FEEDBACKS: SOME FURTHER ISSUES An Editorial Comment

The editorial essay by Shaw et al. (1998) discusses the possible role of deep convective transports of sulfate particles in regulating climate. They suggest that a 30 % increase in the biogenic sulfate aerosol, cycled through enhanced deep convection in a warmer climate, upon sinking back into the convective boundary layer (BL), could increase the albedo of BL clouds by 1.6 % by providing additional cloud condensation nuclei and increasing the droplet number concentration (Charlson et al., 1987). Given a 30 % BL cloud fraction, this would increase the global albedo by 0.5%, and provide a significant negative feedback on climate change. There are many links in the convective components of this argument, where we need a better understanding of the processes and the climatic equilibrium involved (Betts, 1990). I will discuss some of them. The first is whether there will be more transport of air (carrying biogenic sulfur) out of the BL in a warmer climate. This is not proven, and indeed the reverse could be true. While it is true that deep convection is more intense when fueled by a higher BL equivalent potential temperature (as evidenced by lightning: Williams, 1994)