The ancient Greeks used the word hubris to describe vaulting pride that challenged even the gods. Geoengineering is a new word for proposals to counteract climate change with engineering solutions, and it has all the marks of hubris. It does not yet have an accepted definition, but it usually refers to proposals to forestall climate change, not simply to ameliorate its consequences. (By that definition, dikes to contain a rising sea level are not geoengineering, nor are efforts to minimize the sources of greenhouse gases.) The current and growing interest in geoengineering arises from a false hope that, somehow, technology can save us from the consequences of our own growth.

The proposals are many and imaginative. They include ideas such as fertilizing the sea with iron to promote plankton growth and absorb carbon dioxide, replacing fossil fuels by putting floating carpets of amorphous silicon into space to beam renewable energy down to Earth, inject- ing artificial smog or even giant mirrors into the stratosphere to block incoming solar energy, capturing the carbon dioxide emitted by burning coal and injecting it into subterranean caverns or the sea floor, or making clouds whiter so that they reflect solar energy rather than absorbing it.