Carbon dioxide and methane: sources and mitigation

Chemistry of the atmosphere • Carbon dioxide and methane

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Why do international differences limit global emission reductions?

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Different economic development levels and priorities make uniform commitments and enforcement difficult.

Key concepts

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Human sources of carbon dioxide

Combustion of fossil fuels in power stations, vehicles and industry releases carbon dioxide because carbon compounds oxidise to CO2 when burned. Removal of trees by deforestation reduces carbon storage in biomass so less CO2 is absorbed from the atmosphere. Cement production releases CO2 during the chemical conversion of limestone to lime, increasing atmospheric CO2 concentrations.

Human sources of methane

Agricultural activities release methane when ruminant animals digest plant material; microbial fermentation in the gut produces CH4 that animals emit. Flooded rice paddies produce methane because anaerobic microbial decomposition of organic matter in waterlogged soils forms CH4. Decomposing organic waste in landfills emits methane due to anaerobic breakdown. Extraction and transport of fossil fuels can leak methane directly from reservoirs, pipelines and processing equipment.

Actions to reduce carbon dioxide emissions

Replacing fossil fuels with low-carbon electricity from wind, solar and nuclear reduces CO2 because combustion decreases or stops. Improving energy efficiency in buildings, transport and industry reduces energy demand and therefore fuel burning. Reforestation and afforestation increase carbon storage because growing trees absorb CO2 during photosynthesis. Carbon capture and storage (CCS) traps CO2 from power stations or industrial plants and stores it underground, preventing release to the atmosphere.

Actions to reduce methane emissions

Capturing methane from landfill sites and using it for energy prevents direct release and provides a fuel source. Altering livestock management, such as dietary additives and breeding for lower-emission animals, reduces methane produced during digestion. Improved rice-field water management and treatment of manure by anaerobic digesters lower methane production by reducing the time soils or wastes remain anaerobic. Repairing leaks and upgrading infrastructure in the fossil-fuel supply chain prevents methane escape.

Barriers that limit emission reductions

High upfront cost of low-carbon technologies and infrastructure causes slow adoption because governments or businesses prioritise short-term costs. Dependence of some economies on fossil-fuel industries creates political resistance because job losses and revenue declines cause social and economic disruption. Technological limits and long lead times for deployment create delays because some mitigation options require further development or large-scale installation. International coordination challenges prevent uniform action because countries have different priorities, capabilities and responsibilities.

Key notes

Important points to keep in mind

Burning fossil fuels directly increases atmospheric CO2 through oxidation of carbon compounds.

Deforestation reduces CO2 uptake and releases stored carbon when trees are removed or burned.

Ruminant digestion and anaerobic decomposition produce methane, a potent short-term greenhouse gas.

Replacing fossil fuels with renewables reduces CO2 if energy demand and lifecycle emissions are managed.

Methane capture at source both prevents emissions and provides an energy resource.

Costs, technology readiness and political resistance commonly limit rapid adoption of mitigation measures.

Actions that work locally may require international coordination to achieve global emission reductions.

Some mitigation methods create trade-offs, for example between land use for bioenergy and food production.

Short-term warming potential differs between methane and CO2; methane reductions yield faster climate benefits.

Monitoring, reporting and verification are necessary to ensure claimed emission reductions are real.