Abstract
Geoengineering applications by injection of sulfate aerosols into the stratosphere are under consideration as
a measure of last resort to counter global warming. Here adaptation to a potential regional-scale application
to offset the impacts of heat waves is critically examined. The effect of regional-scale sulfate aerosol
emission over California in each of two days of the July 2006 heat wave using the Weather Research Forecast
model with fully coupled chemistry is used to quantify potential reductions in surface temperature as a function
of emission rates in the lower stratosphere. Over the range considered, afternoon temperature reductions scale
almost linearly with emissions. Local meteorological factors yield geographical differences in surface air
temperature sensitivity. For emission rates of approximately 30 µg m-2 s-1 over the region, temperature
decreases of around 7 C result during the middle part of the day over the Central Valley, one of the hardest
hit by the heatwave. Regions more ventilated with oceanic air such as Los Angeles have slightly smaller
reductions. The length of the hottest part of the day is also reduced. Advection effects on the aerosol cloud
must be more carefully forecast for smaller emission regions. Verification of the impacts could be done via
measurements of differences in reflected and surface downward shortwave. Such regional geoengineering
applications with specific near-term target effects but smaller cost and side effects could potentially
provide a means of testing larger scale applications. However, design trade-offs differ from global
applications and the size of the required emissions and the necessity of emission close to the target region
raise substantial concerns. The evaluation of this regional scale application is thus consistent with global
model evaluations emphasizing that mitigation via reduction of fossil fuels remains preferable to considering
geoengineering with sulfate aerosols.
| Note: The present study is motivated by the argument that it is useful for groups whose primary research focus lies elsewhere to contribute to evaluation of potential geoengineering proposals, especially where tools developed for other purposes can contribute at low cost to particular aspects of understanding the issues involved. In this case a setup of the the Weather Research Forecast model with fully coupled chemistry (WRF-Chem) is used to to provide a model-based evaluation of a potential regional application of geoengineering. We regard this as providing initial information that could be used in assessment of such regional applications, about which we share deep reservations. |
Citation Bernstein, D. N., J. D. Neelin, Q. B. Li, and D. Chen, 2012: ould aerosol emissions be used for regional heat wave mitigation? Atmos. Chem. Phys., submitted, 7/2012.