increase in harvestable marine biomass and the consequent reduction in utilization (and release) of carbon by terrestrial biomass.

# **8.2 Limiting Ocean Warming in Critical Areas**

The accumulation of heat in the ocean due to the higher greenhouse gas concentrations increases evaporation and warms surface waters, both of which contribute to the intensification of tropical cyclones and other storms. Already, there are indications that a larger percentage of nascent tropical cyclones are developing into more powerful hurricanes and typhoons (IPCC, 2007a), increasing the damage and inundation occurring along coasts and inland. In addition, warmer than typical ocean temperatures have been increasing the frequency of coral bleaching episodes. Reducing, or at least limiting the rise, in the temperatures of waters in tropical-cyclone formation and intensification regions could be very beneficial.

Approaches for doing this include at least the Latham et al. (2008) suggestion for increasing cloudiness, ocean pipes to cool specific ocean areas (Lovelock and Rapley, 2007), and an emerging approach to increasing ocean surface albedo by injecting small bubbles (Russell Seitz, personal communication). While these approaches have the potential for exerting a global influence if fully deployed, a much more limited and feasible deployment in specific areas could be very beneficial and would also allow testing of the global concept. Even were the climate not changing, exploring the potential for these approaches to limit storm intensification and coral bleaching could be beneficial, especially considering the situations being faced by the increasing numbers of people living in coastal regions and on vulnerable islands.

# **8.3 Limiting High-Latitude Warming and Its Contribution to Sea Level Rise**

The Arctic is already experiencing adverse impacts from the amplified onset of global warming that occurs in high latitudes—and then spreads its effects to lower latitudes. Sea ice retreat is threatening both key species and coastal communities, while melting of glaciers and ice sheets is contributing to sea level rise. These changes have been caused by a relatively small increase in the warming influence in the area, suggesting that a relatively modest reduction in solar radiation into the region could be beneficial. If enhancing the tropospheric or lower stratospheric aerosol loading in the region could be used to exert a cooling influence, the change would also benefit mid-latitudes because the Arctic serves, in effect, as the “air conditioner” for the Northern Hemisphere, creating the cold air that is necessary to sustain mid-latitude weather patterns and storm tracks.

Initial model studies indicate that reduced solar radiation into the region would limit regional and Northern Hemisphere warming while also promoting increased snowfall and building up glaciers and ice sheets, thereby helping to limit sea level rise. In that the stratosphere is at comparatively low altitude in the region and the aerosols only need to be present during the Arctic summer, injection should be relatively inexpensive. Because the Arctic summer troposphere is quite stable and rarely experiences convection, an alternative approach to lower stratospheric injection might be tropospheric injection. This could be achieved, for example, by releasing SO2 from power plant stacks in Europe and North America when meteorological conditions are forecast to carry the air mass into the summertime Arctic. While tropospheric aerosols would have a shorter 31