As the earth warms and the polar ice caps melt because we keep putting more heat-trapping greenhouse gasses into the atmosphere, radical geoengineering schemes have been proposed to break that cycle and keep the climate from changing so fast.
A paper published this week in Proceedings of the National Academy of Sciences looks at five of these schemes -- injecting sulfur dioxide aerosol into the atmosphere to block the sun as a volcanic eruption would; putting giant mirrors into space to deflect the sun; planting large numbers of trees to absorb carbon dioxide; creating biochar (charcoal that's made from burned organic wastes and buried to improve the soil); and burying carbon dioxide -- to see how they would affect sea levels.
The answer is not much. By the year 2100, the scientists say, sea levels are expected to rise by 30 centimeters -- that's nearly a foot -- or more unless we severely cut our greenhouse gas emissions AND use our most aggressive geoengineering.
Giant mirrors or sulfur dioxide aerosols won't cut it, the scientists say. Injecting enough aerosol to produce the equivalent of the 1991 Pinatubo eruption in the Philippines every 18 months would delay a sea level rise by only 40 to 80 years, and sulfur dioxide could cause other problems, as this Atlantic Monthly article points out. Acid rain is a possibility, as is uneven climate change that punishes some countries and not others.
Biochar plus burning biofuels plus burying carbon dioxide could limit the sea level rise to 10 centimeters, or about 4 inches.
As Microsoft Chairman Bill Gates points out in this interesting interview with Technology Review, we have a problem, especially in the U.S.:
The U.S. uses, per person, over twice as much energy as most other rich countries. And so it's easy to say we should cut energy use through better buildings and higher MPG and all sorts of things. But even in the most optimistic case, if the U.S. is cutting its energy intensity by a factor of two, to get to European or Japanese levels, the amount of increased energy needed by poor people during that time frame will mean that there's never going to be a year where the world uses less energy. The only hope is less CO2 per unit of energy. And no: there is no existing technology that at anywhere near economic levels gives us electricity with zero CO2.
Gates, whose foundation is interested in energy, is calling for an "energy miracle" that would start with more government investment for research into ways to cut carbon dioxide emissions.