See below. The issue of stratospheric dynamics strikes me as potentially far from benign. I'm personally uncomfortable with using models which don't model this.
A ---------- Forwarded message ---------- From: Govindasamy Bala <[email protected]> Date: 25 July 2014 11:18 Subject: Geo paper published in Climate Dynamics To: Andrew Lockley <[email protected]>, Ken Caldeira <[email protected]> Hello Andrew, Following is a paper that compares climate effects of sunshades and stratospheric aerosols. Authors are a couple of my students, I and Ken. I am sending this to you so you post this to the geoengineering email list. The main finding is that the diffuse radiation increases almost by a quarter with stratospheric aerosol scheme which leads to an increase in shaded photosynthesis. However, because of a corresponding larger reduction in direct light, the net photosynthesis does not differ too much between the shaded and stratospheric schemes. http://link.springer.com/article/10.1007/s00382-014-2240-3 Modeling of solar radiation management: a comparison of simulations using reduced solar constant and stratospheric sulphate aerosols Sirisha Kalidindi · Govindasamy Bala · Angshuman Modak · Ken Caldeira Abstract The climatic effects of Solar Radiation Management (SRM) geoengineering have been often modeled by simply reducing the solar constant. This is most likely valid only for space sunshades and not for atmosphere and surface based SRM methods. In this study, a global climate model is used to evaluate the differences in the climate response to SRM by uniform solar constant reduction and stratospheric aerosols. Our analysis shows that when global mean warming from a doubling of CO2 is nearly cancelled by both these methods, they are similar when important surface and tropospheric climate variables are considered. However, a difference of 1 K in the global mean stratospheric (61–9.8 hPa) temperature is simulated between the two SRM methods. Further, while the global mean surface diffuse radiation increases by ~23 % and direct radiation decreases by about 9 % in the case of sulphate aerosol SRM method, both direct and diffuse radiation decrease by similar fractional amounts (~1.0 %) when solar constant is reduced. When CO2 fertilization effects from elevated CO2 concentration levels are removed, the contribution from shaded leaves to gross primary productivity (GPP) increases by 1.8 % in aerosol SRM because of increased diffuse light. However, this increase is almost offset by a 15.2 % decline in sunlit contribution due to reduced direct light. Overall both the SRM simulations show similar decrease in GPP (~8 %) and net primary productivity (~3 %). Based on our results we conclude that the climate states produced by a reduction in solar constant and addition of aerosols into the stratosphere can be considered almost similar except for two important aspects: stratospheric temperature change and the consequent implications for the dynamics and the chemistry of the stratosphere and the partitioning of direct versus diffuse radiation reaching the surface. Further, the likely dependence of global hydrological cycle response on aerosol particle size and the latitudinal and height distribution of aerosols is discussed. -- Best wishes, ------------------------------------------------------------------- G. Bala Professor Center for Atmospheric and Oceanic Sciences Indian Institute of Science Bangalore - 560 012 India -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/geoengineering. For more options, visit https://groups.google.com/d/optout.
