Video: How 'geoengineering' could be our last line of defense against climate change

Who would have thought that Earth would be the first planet humanity would terraform? National Geographic tackles our planet's future climate in a new show.

Depending on whom you ask, we're either in for quite an extraordinary-but-manageable amount of climate change already, or well more than we're going to be able to handle gracefully. In either case, it's very likely that the changes to our planet will be so profound that we will at least consider cooling our atmosphere directly, through a process called geoengineering.

Jonathan Latham, pictured in this clip from National Geographic's "Earth Overhaul" show, has invented one of the more benign means of geoengineering, known as Marine Cloud Brightening. It's simple, in principle: clouds floating over the ocean reflect sunlight back into space, so why don't we make them even more reflective by "seeding" them with salt water, which should make them denser.

Of course, that explanation fails to encompass the substantial engineering challenges that must be overcome for this scheme to work. As I wrote in a detailed report on the technology, it could in theory be accomplished by a fleet of 1500 wind-powered vessels that would each transform 30 liters of water per second into a uniform spray of micron-size water droplets.

So what does geoengineering have to do with cities? Only the realization that it's the climate control that makes urban living possible that gave us the idea in the first place.

Here's a fanciful postcard from Germany, c. 1900, depicting a "weather control machine" designed to tune a town's forecast to its optimum.

And here is the famous image of Buckminster Fuller's proposed climate-control dome for Manhattan.

Cities are the places in which we have already mastered the weather. Their vast indoor spaces allow us to carry on our daily activities while hardly ever experiencing the mercurial outdoors. It's only when changes in weather become really extreme -- as in the case of climate change -- that we start considering adjusting the thermostat outside as well as in.

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