Keeping CO₂ Out of the Atmosphere

Carbon dioxide may be kept from release to the atmosphere in power generation by (1) decarbonization or (2) sequestration. Decarbonization refers to reducing the amount of carbon emitted per unit of primary energy generated. Sequestration refers to either capturing CO₂ emitted by fuel combustion before it reaches the free atmosphere or capturing CO₂ already in the atmosphere. A trend from coal to oil to natural gas to hydrogen is a trend toward decarbonization, since each type releases progressively less carbon per unit power generated, with use of hydrogen being carbon free. Unfortunately, Earth does not have geological reservoirs of hydrogen. Also, converting fossil fuels to hydrogen produces more CO₂ than burning the fossil fuel directly. Creating H₂ by electrolysis of water with energy supplied by renewable or nuclear power is not cost effective.

Possible reservoirs for sequestering CO₂ include oceans, forests, soils, depleted natural gas and oil fields, deep saline aquifers, coal seams, and solid mineral carbonates. Capture of CO₂ by plant matter is the simplest form of sequestration, but methods and timescales for keeping the CO₂ from reverting to the atmosphere through decay must be considered. Forests at temperate latitudes may sequester up to 3 billion tons per year although as warming intensifies, soil respiration (loss of CO₂) may increase to the point where forests are net sources instead of sinks of CO₂.

Injection of CO₂ into the deep ocean also has been considered. Such massive amounts of CO₂ added to the ocean would make it somewhat more acidic (carbonic acid). Eventually the CO₂ would diffuse back to the surface after a time depending on how deep and where it is injected.

From these considerations, if CO₂-free fuels for 10-30 TW of power are not available by 2050, enormous quantities of CO₂ will need to be sequestered to reach CO₂ stabilization.

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