Solar Raidation Management (SRM)
Geoengineering encompasses two maijor categories of approaches - the Solar Radiation Management (SRM) and the Carbon Dioxide Removal (CDR). Chapter 7 focuses on assessing the former.
The efficacy of different SRM strategies and climate response to them (in terms of surface air temperature and precipitation rate) as well as to abrupt termination of SRM have been evaluated by the Geoengineering Model Intercomparison Project (GeoMIP) [Kravitz et al., 2011]. Some results are from these studies are:
1. Effecicacy of SRM
As shown in Figure 7.22 (left), GeoMIP simulations have shown that with a continuous 10-year SRM (balancing the 4 × CO2 forcing by a reduction in the total solar irradiance to produce a global top of the atmosphere flux imbalance of less than ±0.1 W m^–2) (b & d), effective slowing-down of temperature increase (b) is possible at the expense of decreased precipitation rate (negative changes in precip. rate in d). Scenarios without SRM and only 4 × CO2 are displayed in (a & d) for comparison.
Figure 7.23 (left) shows the results from the same modeling runs as in Figure 7.22, but putting the results on a global map instead of just showing the zonal averages. Same conclusion in terms of SRM efficacy can be drawn. (a-d) show the change in surface air temperature (°C) averaged over December, January and February (DJF) (top row) and over June, July and August (JJA) (2nd row), without (left column) and with (right column) SRM. (e–h) same as (a–d) but for the change in precipitation (mm day^–1).
2. Side-effect of SRM
Figure 7.24 (left) shows the results from an SRM experiment implemented as an increasing reduction of the total solar irradiance to balance a 1% yr^–1 increase in CO2 concentration until year 50, after which SRM is stopped for the next 20 years.
As can be seen, following the sudden termi-nation of SRM at year 50, in post-SRM atmospheric temperatures and precipitation rates (solid lines) will rapidly increase to the level if were no SRM (dashed lines). These drastic changes in temperature and precipitation rate can easily causing some side effects, such as imbalances in the climate system and great stress in ecosystem.