Driscoll
drew a model of the upper atmosphere on a whiteboard. “Here’s the
troposphere,” he said, drawing an arc. Above that he drew another arc
for the tropopause, which sits between the troposphere and the next arc,
the stratosphere. Most planes fly roughly in the upper troposphere,
occasionally entering the stratosphere. To cool the planet, Driscoll
explained, we’d want to inject reflective particles into the
stratosphere, because it’s too high for rain to wash them out. These
particles might remain floating in the stratosphere for up to two years,
reflecting the light and preventing the sun from heating up the lower
levels of the atmosphere, where we live. Driscoll’s passion is in
creating computer models of how the climate has responded to past
eruptions. He then uses those models to predict the outcomes of
geoengineering projects.
Harvard
physicist and public-policy professor David Keith has suggested that we
could engineer particles into tiny, thin discs with “self-levitating”
properties that could help them remain in the stratosphere for over 20
years. “There’s a lot of talk about ‘particle X,’ or the optimal
particle,” Driscoll said. “You want something that scatters light
without absorbing it.” He added that some scientists have suggested
using soot, a common volcanic byproduct, because it could be
self-levitating. The problem is that data from previous volcanic
eruptions show that soot absorbs low-wavelength light, which causes
unexpected atmospheric effects. If past eruptions like Krakatoa are any
indication—and they should be—massive soot injections would cool most of
the planet, but changes in stratospheric winds would mean that the area
over Eurasia’s valuable farmlands would get hotter. So the unintended
consequences could actually make food security much worse.
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