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Part I: Impacts of Climate-related Geoengineering on Biological Diversity local cooling could be expected to increase upper ocean mixing and nutrient re-supply, with subsequent effects on biodiversity and ecosystems. The possibility that CCN abundance could also be enhanced biologically, particularly in the Southern Ocean, has been suggested,240 but this approach is not generally considered to be either realistic or effective.241 4.2.3 Potential impacts on biodiversity of surface albedo enhancement Land surface The reflectivity (albedo) of the land surface could be increased by whitening the built environment (e.g. roofs and roads);242 developing crops, grasses or shrubs with more reflective foliage;243, 244 or covering “unused” land surface (e.g. deserts) with reflective material.245 These techniques are likely to have varying degrees of climatic effectiveness, cost-effectiveness and achievability. In general, surface albedo changes are less effective than those above or within the atmosphere, since the reflected irradiance has to travel twice through the Earth’s atmosphere before it is returned to space, with energy (heat) losses on both inward and outward journeys.246 Thus such changes would have to be deployed over very large areas to have a significant effect on the global climate. Assuming that the albedo of all the Earth’s land surface could be changed, significant inter-hemispheric climate effects occur in model simulations247 due to the asymmetric inter-hemispheric distribution of land and ocean. Although unrealistic, such results indicate that (as for cloud brightening) the climatic effects of the technique are location-sensitive. While a high degree of localised cooling could potentially benefit ecosystems that are experiencing the adverse consequences of climate change, the “patchy” nature of the cooling might change local systems as much, or possibly more, than the global warming that the schemes are seeking to address. Whitening the built environment could potentially reduce energy use for air conditioning and provide other local benefits.248 It cannot, however, be considered as a viable geoengineering technique, since the maximum possible change in radiative forcing (with all urban surfaces becoming white) has been estimated to counteract
Part I: Impacts of Climate-related Geoengineering on Biological Diversity vegetation of semi-natural grasslands, shrublands and savannah with species or varities of higher albedo is even more questionable. If it could be done, the potential implications for biodiversity, ecosystems and their services are likely to be very high. Non-biological means have been proposed to increase the reflectivity of (stable) desert regions, by covering them with a polyethylene/aluminium membrane.251 The proponent of that scheme considered such areas to be expendable, on the basis that they are largely uninhabitated and sparsely vegetated. Nevertheless, deserts are not devoid of natural life, nor people: both would be highly impacted if such an approach were to be implemented at a climatically-significant scale, with significant negative ecological effects.252 Desert dust also makes an important contribution to marine productivity, providing the main source of iron to most of the global ocean.253 Water surface It has been proposed that the albedo of the surface ocean—and potentially other large water bodies, such an inland seas—might be enhanced through the introduction of microbubbles (“bright water”) on the basis that microbubbles can be effective at enhancing reflectivity at parts per million levels.254 The feasibility of this scheme at the scale required is highly questionable.255 If it were possible, there would be major biodiversity and biogeochemical implications. Not only would there be impacts of decreased light penetration and temperature changes on phytoplankton, but the microbial composition of the sea surface microlayer256 would change, and air-sea exchange rates of CO2 and other gases (highly sensitive to sea surface properties, including bubbles257) would also be affected. Maintaining year round sea-ice cover in the Arctic would be the most effective and ecologically benign form of ocean albedo management. Unfortunately, that option seems increasingly unlikely under current climate change trajectories.258 251 Gaskill (2004). 252 The Royal Society (2009). 253 Jickells et al. (2005). 254 Seitz (2011). 255 Robock (2011). 256 Cunliffe et al. (2011). 257 Woolf (2005). 258 Meier et al. (2007). 53
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