Climate Mitigation Strategies: How to Reduce Greenhouse Gas Emissions

The Energy Transformation

Electricity and heat production account for approximately 25 percent of global greenhouse gas emissions, making the power sector the single largest source of CO2 and the sector where decarbonization has progressed fastest. The economics of renewable energy have shifted dramatically since 2010. The levelized cost of solar photovoltaic electricity has fallen roughly 90 percent, from about $0.36 per kilowatt-hour to under $0.04 in favorable locations. Onshore wind costs have dropped approximately 70 percent over the same period. In most of the world, building new solar or wind capacity is now cheaper than building new coal or gas plants, and in many regions, new renewables are cheaper than continuing to operate existing fossil fuel plants.

Global renewable energy additions exceeded 500 gigawatts per year by 2024, with solar alone accounting for over 400 GW of new capacity annually by 2025. However, achieving net-zero-aligned electricity systems requires tripling the current rate of deployment. The International Energy Agency's Net Zero by 2050 scenario calls for renewables to provide roughly 90 percent of global electricity by 2050, up from approximately 30 percent in 2025 (including hydropower). This requires not only continued growth in solar and wind but also massive expansion of electricity grids, energy storage, and flexible demand management.

The intermittency of solar and wind, which generate electricity only when the sun shines or the wind blows, is the central technical challenge of a renewable-dominated grid. Solutions include battery storage (lithium-ion battery pack costs have fallen from approximately $1,100 per kilowatt-hour in 2010 to under $140 by 2024), pumped hydro storage (which accounts for 95 percent of global installed storage capacity), demand-side flexibility (shifting electricity consumption to match supply through smart charging, thermal storage, and industrial load shifting), expanded grid interconnection (allowing regions with surplus renewable generation to export to regions with deficits), and firm low-carbon generation from nuclear, geothermal, or natural gas with carbon capture to fill gaps during extended periods of low wind and solar output.

Nuclear energy currently provides approximately 10 percent of global electricity with near-zero operational emissions. Existing nuclear plants represent the single largest source of low-carbon electricity in many countries, and extending their operating lifetimes is among the most cost-effective climate mitigation measures available. New conventional nuclear plants have faced persistent cost overruns and construction delays, particularly in Western countries, though South Korea, China, and the UAE have built plants on time and on budget. Small modular reactors (SMRs), factory-built units of 50 to 300 MW, are in advanced development with several designs expected to receive regulatory approval by 2030. Their smaller size and modular construction may resolve the cost and scheduling problems that have plagued large reactor projects.

Electrification of Transport and Heating

Transportation accounts for roughly 16 percent of global emissions, with road vehicles responsible for about three-quarters of that total. Electric vehicles are approaching purchase price parity with conventional internal combustion vehicles as battery costs decline. In 2024, global EV sales exceeded 17 million units, representing roughly 20 percent of new car sales. China leads in both production and adoption, followed by Europe and the United States. Over their full lifecycle, including manufacturing and electricity generation, EVs produce 50 to 70 percent lower greenhouse gas emissions than equivalent gasoline or diesel vehicles in countries with average grid carbon intensity, and the advantage increases as grids decarbonize.

The electrification of road transport faces remaining challenges in heavy-duty trucking, where battery weight and charging time are more significant constraints. Battery-electric trucks are viable for routes under 500 kilometers, and improving battery energy density is extending this range. For long-haul trucking, hydrogen fuel cells offer an alternative, converting hydrogen gas to electricity in an onboard fuel cell with water as the only tailpipe emission. The competitiveness of hydrogen trucks depends on the cost of green hydrogen (produced by electrolyzing water using renewable electricity), which has fallen but remains roughly twice the cost of gray hydrogen (produced from natural gas without carbon capture).

Building heating accounts for approximately 10 percent of global emissions, predominantly from burning natural gas, oil, and coal in furnaces and boilers. Heat pumps, which move heat from outdoor air (or ground) into buildings using a refrigeration cycle, deliver 3 to 5 units of heat for every unit of electricity consumed, making them 300 to 500 percent efficient compared to the 90 to 95 percent efficiency of a good gas furnace. In well-insulated buildings, modern cold-climate heat pumps operate effectively at outdoor temperatures as low as minus 25 degrees Celsius. Replacing fossil heating with heat pumps reduces building heating emissions by 50 to 80 percent, depending on the carbon intensity of the local electricity grid, and the savings increase as the grid decarbonizes.

Heat pump adoption has accelerated rapidly, with European sales doubling between 2020 and 2023 following natural gas price spikes and policy incentives. The United States passed a milestone in 2022 when heat pump shipments exceeded gas furnace shipments for the first time. The primary barriers to faster adoption are upfront cost (roughly double that of a gas furnace, though operating costs are lower), contractor familiarity, electrical panel capacity in older homes, and consumer awareness.

Decarbonizing Hard-to-Abate Sectors

Several industrial sectors produce emissions that cannot be eliminated simply by switching to renewable electricity because their CO2 comes from chemical processes inherent to production, not just from energy inputs. These "hard-to-abate" sectors, primarily cement, steel, and chemicals, account for roughly 20 percent of global emissions and require different mitigation strategies.

Cement production releases CO2 in two ways: from burning fuel to heat kilns to approximately 1,450 degrees Celsius, and from the calcination of limestone (CaCO3) to produce clinker (CaO + CO2). The second source, process emissions, accounts for roughly 60 percent of cement's carbon footprint and cannot be eliminated by switching fuels. Mitigation options include reducing the clinker-to-cement ratio by blending clinker with supplementary materials (fly ash, ground granulated blast furnace slag, calcined clay), developing alternative binders that do not require calcination, and capturing CO2 from kiln exhaust. Carbon capture and storage (CCS) is likely necessary for fully decarbonizing cement production, and several pilot projects are operating at commercial cement plants in Norway, the UK, and Canada.

Steel production currently relies heavily on blast furnaces that use coal (in the form of coke) as both a fuel and a chemical reducing agent to remove oxygen from iron ore. The primary low-carbon alternative is direct reduction of iron using hydrogen instead of coal, producing water vapor instead of CO2. Sweden's HYBRIT project, a collaboration between steelmaker SSAB, mining company LKAB, and energy company Vattenfall, delivered the world's first fossil-free steel to a commercial customer (Volvo) in 2021 and is scaling to full commercial production. Several other hydrogen-based steel projects are under development in Europe, Australia, and the Middle East. Electric arc furnaces, which melt scrap steel using electricity, already produce about 30 percent of global steel with much lower emissions, and their role will expand as more scrap becomes available and electricity decarbonizes.

Aviation and shipping together account for roughly 5 percent of global emissions and face particularly difficult decarbonization challenges because of the energy density requirements of long-distance transport. Batteries are too heavy for commercial aircraft on routes longer than about 500 kilometers. Sustainable aviation fuels (SAFs), including biofuels from waste cooking oil or agricultural residues and synthetic fuels produced from green hydrogen and captured CO2, can reduce aviation emissions by 50 to 80 percent compared to conventional jet fuel on a lifecycle basis. Current SAF production covers less than 1 percent of global jet fuel demand, and scaling production is a major challenge. Maritime shipping is exploring ammonia (NH3) and methanol as zero or low-carbon fuels, with the first ammonia-fueled commercial vessels expected to enter service by 2027.

Carbon Removal: Closing the Gap

Most scenarios that limit warming to 1.5 or 2 degrees require some amount of carbon dioxide removal (CDR) to compensate for residual emissions from sectors that cannot be fully decarbonized, and potentially to reduce atmospheric CO2 concentrations if warming overshoots the target. Carbon removal approaches fall into two broad categories: nature-based solutions that enhance biological carbon uptake, and engineered solutions that use industrial processes to capture CO2 from the atmosphere.

Nature-based carbon removal includes reforestation (planting trees on previously forested land), afforestation (planting trees where none previously grew), improved forest management (extending rotation lengths, reducing harvest intensity), soil carbon enhancement (cover cropping, reduced tillage, biochar application), and coastal ecosystem restoration (mangroves, seagrasses, salt marshes, collectively called "blue carbon"). These approaches are relatively inexpensive ($5 to $50 per tonne of CO2) and provide co-benefits including biodiversity conservation, flood protection, and improved soil fertility. However, their total potential is limited to roughly 3 to 5 billion tonnes of CO2 per year, and the stored carbon is vulnerable to release through wildfire, drought, disease, or land-use change.

Direct air capture (DAC) uses chemical processes to extract CO2 directly from ambient air, where it exists at a concentration of approximately 425 parts per million. The captured CO2 can be permanently stored in geological formations (depleted oil and gas reservoirs, saline aquifers, or basalt formations where it mineralizes) or used as a feedstock for synthetic fuels, building materials, or other products. Current DAC costs range from $400 to $1,000 per tonne of CO2, far higher than most mitigation alternatives but declining as the technology scales. The largest operating DAC facility, Climeworks' Orca plant in Iceland, captures approximately 4,000 tonnes per year, and its successor Mammoth plant (36,000 tonnes/year) began operations in 2024. The U.S. Department of Energy's Direct Air Capture Hubs program has funded four regional hubs targeting 1 million tonnes each per year.

Bioenergy with carbon capture and storage (BECCS) involves growing biomass that absorbs CO2 from the atmosphere, burning or gasifying it to produce energy, and capturing the resulting CO2 emissions for geological storage. Because the carbon was originally removed from the atmosphere by the growing plants, the net effect is negative emissions. BECCS faces concerns about land-use competition with food production, biodiversity impacts of monoculture energy crops, and the availability of geological storage sites near biomass sources. Enhanced weathering, which involves spreading crusite silicate minerals (such as basalt) on agricultural land where they react with CO2 in rainwater to form stable carbonates, is another engineered approach under active research, with several field trials reporting promising results.

Carbon Budgets and Emissions Pathways

The concept of a carbon budget translates the temperature targets of the Paris Agreement into a concrete quantity of CO2 that humanity can still emit. Because global temperature is approximately proportional to cumulative CO2 emissions (a relationship called the transient climate response to cumulative emissions, or TCRE), limiting warming to a specific level implies a fixed total budget of allowable emissions from today forward.

The IPCC's Sixth Assessment Report estimated the remaining carbon budget for a 50 percent probability of limiting warming to 1.5 degrees at approximately 500 billion tonnes of CO2 from the beginning of 2020. At the 2024 emission rate of roughly 40 billion tonnes per year, this budget would be exhausted by approximately 2032. The budget for 2 degrees (67 percent probability) is approximately 1,150 billion tonnes, lasting about 28 years at current rates. Every year of delay in reducing emissions shrinks the remaining budget and requires steeper subsequent cuts, making rapid near-term action disproportionately valuable.

Emissions pathways consistent with 1.5 degrees generally require global CO2 emissions to peak before 2025 (which may have occurred, as 2024 showed signs of plateau), decline approximately 45 percent below 2010 levels by 2030, and reach net zero by approximately 2050. For 2 degrees, the timeline is somewhat less compressed: emissions must peak before 2025, decline roughly 25 percent by 2030, and reach net zero by approximately 2070. All 1.5-degree pathways assessed by the IPCC involve some degree of temperature overshoot followed by drawdown through carbon removal, meaning that even with aggressive mitigation, temperatures will likely temporarily exceed 1.5 degrees before CDR brings them back down later in the century.

The distribution of remaining emissions across sectors and countries is fundamentally a question of equity and justice. Developing nations argue, with substantial justification, that wealthy nations bear historical responsibility for the majority of cumulative emissions and should therefore decarbonize faster and provide financial and technological support for transitions in developing countries. The Paris Agreement acknowledges this principle through "common but differentiated responsibilities," and climate finance from developed to developing nations (targeted at $100 billion per year, a goal that was achieved in 2023 with significant questions about how the total was counted) is a central element of international climate negotiations.

Policy Tools for Mitigation

Effective climate mitigation requires policy frameworks that redirect investment, change incentives, and accelerate technology deployment. The primary policy instruments include carbon pricing, regulations and standards, subsidies and tax incentives, and public investment in research and infrastructure.

Carbon pricing, through either carbon taxes or cap-and-trade systems, puts a direct cost on greenhouse gas emissions, making fossil fuels more expensive relative to clean alternatives and incentivizing emissions reductions wherever they are cheapest. The EU Emissions Trading System (EU ETS), the world's largest carbon market, covers roughly 40 percent of EU emissions and reached prices above 100 euros per tonne in 2023 before settling in the 60-80 euro range. Carbon border adjustment mechanisms (CBAMs), first implemented by the EU in 2026, impose tariffs on imports from countries without comparable carbon prices, addressing the competitiveness concern that has historically limited carbon pricing ambition.

Regulatory standards, including vehicle emission standards, building energy codes, renewable portfolio standards for utilities, and methane emission rules for oil and gas operations, have driven significant emissions reductions. The United States' Inflation Reduction Act (IRA) of 2022 took a different approach, using approximately $370 billion in tax credits and subsidies rather than regulations or carbon pricing to incentivize clean energy deployment. The IRA's production tax credits for clean electricity, investment tax credits for solar and storage, and consumer rebates for EVs and heat pumps have accelerated clean energy investment substantially, with over $300 billion in announced clean energy manufacturing investments in the two years following its passage.