Geoengineering: Can Humans Reverse Climate Change?
Solar radiation management, while potentially the fastest way to cool the planet, also is temporary and could potentially have many side effects. One of the proposals currently being discussed is the creation of manmade volcanic eruptions. Sulfide gases would be injected into the stratosphere every one to four years, providing the earth with a "grace period" of up to 20 years before major cutbacks in greenhouse gas emissions would be required [Source: UCAR]. Unfortunately, this technique could thin the ozone layer if enough aerosol is injected into polar stratospheric clouds. Other negative effects include changing weather patterns, drought, acid rain and respiratory problems in humans. If done properly, however, this technique could potentially drop average temperatures 0.6 degrees Celsius [Source: 21st Century Challenges]. A less risky solar radiation management plan involves whitening of marine clouds. Ocean spray is released into the atmosphere to increase the reflectiveness of clouds. The extra changes the size of the water particles in existing clouds, making them whiter. This technique can be stopped at any time and is part of the natural process of "ocean spray". It can be deployed quickly and rolled out cheaply and effectively, though it could potentially interfere with wind and weather patterns [Source: Guardian]. This problem also does not address ocean acidification or ways to actually decrease the amount of CO2.
While solar radiation management only looks at decreasing overall temperature, carbon sequestration looks for ways to decrease overall CO2 levels. Iron deposition into the ocean is one method of carbon sequestration. The iron encourages phytoplankton growth, which removes carbon from the atmosphere, potentially on a permanent basis. While this sounds promising, there is no way to predict how this could effect marine life and nutrient balance in the ocean and could lead to poisonous algae spread [Source: Spiegel]. There are two methods of geoengineering that do not have harmful side effects: reforestation/afforestation and biochar. Reforestation is the process of replanting trees in cleared areas and afforestation is planting trees in areas that were never forest or haven't been for years. Currently, deforestation accounts for 25% of the world's greenhouse gase emissions [Source: Monga Bay]. While planting trees would help to decrease the amount of CO2, the time it takes for trees to regrow and biomass to rebuild is significant. Reforestation could be used alongside biochar. Biochar is charcoal made through pyrolysis of biomass, which is then buried and mixed with normal soil. Not only does it make the soil fertile, it holds potential for long-term carbon storage, possibly for millenia. Craig Sams, founder of Carbon Gold, believes biochar could potentially reduce CO2 levels to pre-industrial levels by 2050 if it were used in 2.5% of the world's agricultural fertilizer [Source: Popular Mechanics]. Biochar is easily measured, making it great to figure out effectiveness of its carbon sequestration and it is at much lower risk of returning to the atmosphere than living organisms since it is mainly inert [Source: Treehugger].
While many of the "quick-fix" geoengineering proposals have many negative side effects, they are mostly presented in worst-case scenario and are generally temporary. The more long-term solutions like reforestation and the usage of biochar may work better, but it takes longer to see the effects. Either way, no geoengineering technique will be effective if the average global carbon emission does not decrease.