Geoengineering solutions to global warming

Taking man-made greenhouse gases out of the picture, the world should probably think about geoengineering.

That was the message last week when Jonathan Katz, professor in the Department of Physics and McDonnell Center for the Space Sciences at Washington University, spoke to Lab employees.

The National Academy of Sciences defines geoengineering as "options that would involve large-scale engineering of our environment in order to combat or counteract the effects of changes in atmospheric chemistry."

Katz' idea of geoengineering involves trying to curb global warming with stratospheric aerosols. He said manmade aerosols could decrease the amount of light reflected on earth from the sun (albedo).

However, this type of geoengineering does not reduce greenhouse gas concentrations in the atmosphere. More likely, this kind of approach, which can be deployed quite quickly, could be seen as a "quick fix" while other greenhouse gas remediation techniques are put in place.

"We could mitigate the increase in earth's albedo for visible and near infrared solar radiation with manmade aerosols," Katz said.

Katz said global warming is nothing to be "frantic" about. Instead he said that climate through the ages is always unstable between ice ages and interglacial periods. "Geoengineering is required to maintain the present climate, with or without greenhouse gases," he said.

This type of geoengineering is similar to the natural cooling of the earth after a large volcano erupts, in which ashes and aerosols are spewed into the upper atmosphere, cooling the earth's surface. Lab research shows that ocean warming and sea level rise in the 20th century were substantially reduced by the 1883 eruption of the Krakatoa volcano in Indonesia. The researchers found volcanic aerosols blocked sunlight and caused the ocean surface to cool.

"This shows you that it works," said Katz, comparing manmade aerosols to volcanic sulfate aerosols.

Katz pointed out three advantages to geoengineering with aerosols: rapid deployment, reversible and cheap. He said the aerosols could be injected into the atmosphere by three methods: aircraft (limited to a little over 15 kilometers), naval guns (can travel up to 24 kilometers) and rockets, which are the most efficient from 20 to 50 kilometers.

However, Katz said before any method could be deployed, more research to overcome mostly technical issues must be conducted.

"It is by no means clear that you can make these work," he said. "There's more talk about this than there is work. There could be real useful laboratory work in this area, but it just hasn't been done yet."

The talk was part of the Lab's Physical and Life Sciences Directorate Colloquium series.