For better or worse, a fifth of an Alaska Air would not be expensive. One well-known estimate from 2012 suggested that fourteen big cargo aircraft—Boeing 747s, for example—could pull a Pinatubo for a little more than $1 billion a year. But commercial jets are not designed to fly into the stratosphere (the higher one places the sulfur, the longer it will stay aloft). Specially designed planes could be more effective and cost only $2 to $3 billion a year to operate. Either way, it is financially feasible. The cost for a decade of counteracting most of the impact of carbon dioxide, the Harvard
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