Plan B: 7 ways to ‘engineer’ climate
Berlin: Dismissed a decade ago as far-fetched and dangerous, schemes to tame global warming by engineering the climate have migrated from the margins of policy debate towards centre stage.
“Plan A” remains tackling the problem at its source. But efforts to sharply reduce greenhouse gas emissions have fallen woefully short and cannot, most scientists agree, avert catastrophic climate change on their own.
Here is a “Plan B” menu of geoengineering solutions that can be broken down into two categories: dimming the sun, which remains highly controversial, and capturing carbon dioxide (CO2).
The goal is simple: prevent some of the sun's rays from hitting the planet's surface, forcing them instead back up into space.
One idea worthy of a “Star Wars” sequel would assemble giant orbiting mirrors to deflect a bit of Earth-bound radiation.
A more feasible scheme — experiments are scheduled for next fall in Arizona — would inject tiny reflective particles into the stratosphere.
Nature sometimes does the same: Debris from the 1991 eruption of Mount Pinatubo in the Philippines lowered the planet's average surface temperature for a year or two afterwards.
Scientists have also calculated ways to alter clouds that could help beat the heat. One is to brighten the white, billowy ocean clouds that rebound sunlight back up. Another would thin cirrus clouds, which unlike other types absorb more heat than they reflect.
Even if it works as intended, solar radiation management would do nothing to reduce atmospheric CO2, which is making oceans too acidic. There is also the danger of knock-on consequences, including changes in rainfall patterns, and what scientists call “termination shock” — a sudden warming if the system were to fail. Microscopic ocean plants called phytoplankton gobble up carbon dioxide and drag it to the bottom of the ocean when they die.
Colony size is limited by a lack of natural iron, but experiments have shown that sowing the ocean with iron sulphate powder creates large blooms.
Again, scientists worry about unintended impacts. Die-offs of plankton, for example, use up oxygen, which could create massive "dead zones" in the oceans, something already on the rise.
Natural weathering of rocks — a chemical process — removes about one billion tonnes of CO2 from the atmosphere every year, about two percent of total manmade C02 emissions. What if technology could accelerate that process?
Spreading a powdered form of a greenish iron silicate called olivine across certain landscapes does just that, experiments have shown. Enhanced weathering could probably be rapidly scaled up, but it would be expensive to mine and mill enough olivine to make a difference. Biochar is charcoal made by heating plant waste over long periods in low-oxygen conditions.