7 ways to control our climate
Dismissed a decade ago as dangerous, schemes to tame global warming by engineering the climate have migrated from the margins of policy debates towards centre-stage. Here is a menu of “Plan B” solutions to save our planet:
1 Direct CO2 capture Experiments have shown it is possible to suck carbon dioxide directly from the air, converting it into fuel pellets or storing it underground. A Canadian company backed by Microsoft co-founder Bill Gates launched a pilot facility in Canada in 2015.
2 Massive afforestation Extensive planting of trees could slow the concentration of CO2 in the atmosphere, which currently stands at more than 400 parts per million.
3 Bio-enrgy with carbon capture Bioenergy with carbon capture and storage (BECCS) marries a natural process with a high-tech one. First, plant rapeseed, sugarcane, corn or "second-generation" biofuel crops which pull CO2 from the air while growing. Then, while burning the harvested plants for energy, sequester the CO2 produced. The result is "negative emissions".
4 Ocean fertilisation Microscopic ocean plants called phytoplankton gobble up CO2 and drag it to the bottom of the ocean when they die. Their 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.
5 Enhanced weathering Natural weathering of rocks removes about one billion tonnes of CO2 from the atmosphere every year, about two percent of total man-made 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.
6 Biochar Biochar is charcoal made by heating plant waste over long periods in low-oxygen conditions, for example buried in the ground. It can store CO2 for long periods, and also enriches soil.
7 Solar radiation management Unlike other strategies, solar radiation management does not target CO2. The goal is simple: prevent some of the sun's rays from hitting the planet's surface, forcing them back up into space. One idea is to inject or spray tiny reflective particles into the stratosphere - possible with balloons, aircraft or through giant tubes.