Carbon dioxide released to the atmosphereAtmosphere can be captured and removed. Annual removal of up to 20 billion tons of CO2 has been proposed as necessary to avoid significant climate changeClimate change. Reduction options include growing more trees, using much more wood in building, capturing carbon in coastal systems, in the ocean, in agricultural soils, accelerated mineralization, using biomassBiomass for energy and sequestering its carbon dioxide, capturing carbon dioxide from power plants and industrial sources and sequestering the carbon dioxide, and capturing carbon dioxide directly from the air and sequestering it or using it to make synthetic fuels. All approaches face challenges of scale and some approaches are expensive. GeoengineeringGeoengineering adjusts characteristics of the Earth’s system to reduce some of the effects of greenhouse gases in the atmosphereAtmosphere.