Protecting vital infrastructure as sea levels rise

stretch across the chilly landscape of Iceland. Chris Binnie, a U.K.-based consultant hydrological engineer, sees no chance of the idea being put into practice. “It is totally unrealistic,” he says.

Spraying droplets into the atmosphere

Even if this brute force approach were feasible, trying to build up the ice caps might well prove futile if the world continues to warm. There may, however, be a subtler approach that will both add ice to the ice caps and ensure it stays there for millennia.

An old idea for fighting climate change is to spray fine sulphate droplets into the stratosphere, where they would reflect some incoming sunlight and so cool the globe. Rather than spreading the stuff around the planet as is currently being considered, sulphates might be deployed more selectively at high latitudes, acting as parasols for the polar regions. This has been suggested as a way to preserve the vanishing sea ice in the Arctic Ocean, but it could also have a fortunate side effect. “We did some climate simulations with reduced solar radiation over the Arctic and Antarctic,” says Ken Caldeira of Stanford University in California. “Greenhouse gases will still be warming equatorial regions, so water is evaporating and the atmosphere is moister.

The deflection of sunlight cools high-latitude air masses, so that moisture comes down as snowfall.”

Snow that lands high on an ice cap will stick there, gradually turn to ice, and not return to the seas for many thousands of years. The numbers are promising. Greenland alone might take up as much as a centimeter of sea level per year. If the polar cooling also slows down the flow of outlet glaciers, that might more than make up for the rise in sea level.

Or will it? The notion of engineering lower sea levels remains a highly speculative topic and, as with geoengineering measures intended to cool the planet, the very idea of deliberately messing about with the delicate mechanisms of our planet scares many people. Even the enthusiasts say that it could only be part of the answer.

“If the world doesn’t control emissions, I’m pretty sure that no geoengineering solution will work - and it would potentially create other side effects and false promises,” says MacCracken. “But if we do get on a path to curbing emissions dramatically — down 50 percent by 2050, say — then the question becomes, can geoengineering help with the