Passive removal through forests and soils
Tree planting and afforestation remove CO2 passively as photosynthesis converts atmospheric carbon into biomass. Forests sequester carbon for decades or centuries, but they are vulnerable to logging, wildfire, and pest outbreaks that release it again. Soil carbon sequestration occurs when organic matter is incorporated into soil and stabilized by minerals; no-till agriculture and managed grazing can increase soil carbon stocks, though the rate is slow (fractional tons per hectare per year). Both approaches are inexpensive but have low permanent sequestration rates and compete for land with food and fiber production.
Ocean and chemical pathways at scale
Ocean alkalinity enhancement and direct air capture (DAC) with carbon storage are technological approaches. Ocean approaches aim to increase the ocean's capacity to absorb CO2; chemical methods use sorbents to directly pull CO2 from ambient air and compress it for storage or use. Bioenergy with carbon capture and storage (BECCS) grows biomass, burns it for energy, captures the CO2 from flue gas, and stores it underground. Mineral carbonation involves reacting rocks with CO2 to lock carbon into solid minerals. These approaches are expensive (USD 100-1000 per ton of CO2) but can achieve permanent sequestration if storage integrity is maintained.
Comparing feasibility and cost by scale
Forests and soils are lowest cost but limited by land availability and permanence. DAC scales to billions of tons but requires massive energy input and infrastructure. Ocean methods have the largest theoretical potential but are nascent and poorly understood at scale. The mix of approaches needed to achieve net-zero emissions will likely use all pathways: immediate emissions reductions, then large-scale cheaper removal (forests, soil) for legacy carbon, and high-cost technological approaches for residual emissions where other options are unavailable. No single approach solves the problem.