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It is essential to remove carbonfrom the air to combat global warming. Methods likereforestation and afforestation involve planting trees to absorb CO2. But they are vulnerable to forest fires. Carbon capture and storage (CCS)technology captures CO2 from industrial sources and stores it underground.Soil carbon sequestration practices, such as no-till farming, can storemore carbon in the ground. Direct air capture (DAC) technologiesremove CO2 directly from the air, for storage underground. Enhancedrock weathering and ocean alkalinity enhancement may be able to remove verylarge amounts of CO2, more cheaply than DAC, but their effects are hard tomeasure.