Aerosols, Global Climate, and the Human Health Co-Benefits of Climate Change Mitigation - Aerosols: Measurement, Dosimetry, and Health Effects - page 350

that past large volcanic eruptions have. For example, the June 1991 eruption of Mount Pinatubo sent
ine ash and gases high into the stratosphere, forming a large volcanic cloud that drifted around the
world. The sulfur dioxide (SO 2 ) in this cloud—about 22 million tons—combined with water to form
droplets of sulfuric acid, a type of sulfate particles, blocking some of the sunlight from reaching the
Earth, thereby cooling temperatures in some regions of the world by as much as 0.5°C (Kious and
Tilling 1996). One recent analysis estimated that annual aerosol injections of 5-10 Mton of sulfate
aerosol (delivering a constant 4 W m −2 reduction in radiative forcing, similar to a 1991 Pinatubo
eruption every 18 months) could delay climate-change-related sea-level rise by 40-80 years (Moore
et al., 2010). However, they note that such aerosol injections fail cost-beneit analysis unless they
can be maintained indeinitely, and that, if ever stopped, the climate sea-level rise effects would
then be “dramatic.” In addition, as noted for the actual Pinatubo eruption itself, the resultant cooling
from sulfate injection is not experienced evenly across the globe, and is unlikely to align with GHG
heating effects in latitude, potentially inducing other, new unplanned weather pattern changes, such
as changes in spatial precipitation patterns (Goldstein et al., 2010). Also, as discussed earlier, these
sulfates have been associated with signiicant adverse human health effects, including increased
risk of premature death. Thus, as discussed in Smith et al. (2010), any such geoengineering needs to
be analyzed carefully for potential unintended consequences and uncertainties.
13.5 ANCILLARY HEALTH BENEFITS OF CLIMATE CHANGE MITIGATION
Policies designed to avert the course of climate change would eventually result in human health ben-
eits directly associated with lessened global temperature changes and associated impacts, but many
would also bring more immediate ancillary health beneits from reduced ground-level air pollution
in the short term (Swart et al., 2004; Haines et al., 2007; Thurston, 2007; Smith et al., 2008; Walsh,
2008). Fossil fuel combustion processes that generate GHGs also emit other harmful air pollutants,
such as toxic metals and OC. Several measures aimed at reducing GHG emissions can also improve
local air quality, most notably PM air pollution. Further, whereas the beneits from climate change
mitigation would materialize far in the future, these co-beneits, or ancillary beneits, would occur
in the short term. Similarly, policies aimed at short-term improvements in air quality could lower
GHG emissions. Much of the discussion that follows of the co-beneits of air pollution mitigation is
further detailed in Bell et al. (2008).
13.5.1 F raMework oF c liMate M itigation c o -b eneFits a ssessMent
Figure 13.4 describes the relationships among the health consequences of climate change and air qual-
ity policies and the general framework of how these responses can be assessed. Air quality policies
are routinely evaluated in terms of the estimated health outcomes avoided and their economic impact
(USEPA, 1997, 1999). However, assessment of the health impacts of GHG strategies often considers
only consequences in the far future (i.e., left side of Figure 13.1), without integration of the short-term
beneits of related policies (Ebi et al., 2006). Well-informed public health and environmental strate-
gies require full consideration of consequences, including co-beneits and potential ancillary harms.
A broad array of tools to evaluate the health-related ancillary costs and beneits of climate change
is currently available, and some examples are provided in italics in Figure 13.4. As described in detail
in Bell et al. (2008), the general structure for most assessments involves three key steps: (1) estimating
changes in air pollutant concentrations, comparing levels in response to GHG mitigation to concentra-
tions under a baseline “business-as-usual” scenario; (2) estimating the adverse health impacts avoided
from reduced air pollution; and (3) for some studies, estimating the monetary beneit from these averted
health consequences, often with comparison to the cost of the climate change mitigation measure.
The irst step in such a co-beneit analysis is often the development of emissions scenarios and
information regarding how emissions translate into pollutant concentrations, such as with air qual-
ity modeling systems. The second step employs concentration-response functions from existing