Climate Change Mitigation: Renewables and Carbon Sinks

Climate change mitigation is the set of actions that reduce greenhouse gas emissions or remove carbon dioxide from the atmosphere, including replacing fossil fuels with renewable energy, improving energy efficiency, protecting and expanding carbon sinks such as forests and soils, and policies such as carbon pricing. In brief: to limit warming to 1.5 °C, the IPCC finds that global CO₂ emissions need to fall by about 45% from 2010 levels by 2030 and reach net zero around 2050. Solar and wind power have become cheaper, electrification of transport and heating is growing, and nature-based sinks can absorb carbon, but they cannot replace the cuts in fossil fuel emissions.

Mitigation addresses the cause of climate change, in contrast to adaptation, which deals with the effects. This guide explains the main ways to cut emissions, how carbon sinks and carbon removal work, which policies are used, compares the options in a table, works through calculations, outlines the history of climate agreements and corrects common mistakes.

How can the energy system be decarbonized?

Burning coal, oil and gas is the largest source of emissions, so replacing them with low-carbon sources is central.

• Solar power: photovoltaic panels and solar thermal plants. The cost of solar electricity has fallen by around 90% since 2010 according to IRENA, making it the cheapest new source of electricity in many places.
• Wind power: onshore and offshore turbines. They are also now cost-competitive in many regions.
• Hydropower, geothermal and bioenergy: established renewable sources, though their potential is limited by geography and, in the case of dams and biomass, by environmental trade-offs.
• Nuclear power: low in emissions during operation and a source of steady power, but expensive and slow to build in some countries, with questions about waste and safety.
• Grids and storage: because wind and sun vary, batteries, pumped hydro, flexible demand, and stronger power lines are needed. Green hydrogen can help in industry and heavy transport.
• Fuel switching and phase-out of coal: moving from coal to gas reduces CO₂ per unit of energy by around half, but methane leaks must be controlled, and long-term goals require phasing out unabated fossil fuels.

How can energy demand and emissions in other sectors be cut?

• Energy efficiency: insulation, efficient appliances and LED lights, and better industrial processes. The cheapest energy is the energy that is not used.
• Electrification: electric vehicles, heat pumps and electric industrial heating, powered by clean electricity.
• Transport: public transport, cycling, walking, rail, more efficient aircraft and ships and lower-carbon fuels.
• Industry: cleaner cement and steel, recycling and the circular economy.
• Agriculture and food: lower methane from livestock and rice, better fertilizer use, less food waste and diets with fewer high-emission foods.
• Methane control: fixing leaks in oil and gas systems, and capturing methane from landfills, which is a fast way to cut warming.

What are carbon sinks and carbon removal?

A carbon sink absorbs more carbon than it releases. The main natural sinks are the oceans and land ecosystems, which together absorb about half of human CO₂ emissions each year. Forests, soils, peatlands, wetlands, mangroves and seagrass beds store carbon. Protecting existing forests and peatlands, ending deforestation, restoring degraded land and planting trees in suitable places are important, but sinks have limits: they take decades to grow, can be lost to fire, drought or logging, and storing carbon in soil can be reversed. Most scientists stress that natural sinks complement and do not replace emission cuts.

Technological carbon removal includes bioenergy with carbon capture and storage (BECCS), direct air capture with storage (DACCS) and enhanced rock weathering. Carbon capture and storage (CCS) captures CO₂ from power plants and industry and stores it underground. These technologies exist at small scale, and most pathways to 1.5 °C assume some use of them, although their cost, energy use and scale-up remain uncertain.

Which policies support mitigation?

Carbon pricing, through a tax or an emissions trading system such as the EU Emissions Trading System, makes polluters pay for emissions. Governments also use regulations (efficiency standards, bans on coal), subsidies and public investment for clean energy, planning for public transport and building standards, and research funding. At the international level, the Paris Agreement of 2015 commits countries to limit warming to well below 2 °C and to pursue 1.5 °C, and each country sets its own “nationally determined contributions.” Many countries and companies have set net-zero targets, mostly for 2050 to 2070. Net zero means that any remaining emissions are balanced by removals.

Mitigation options compared

Worked example: emissions saved

The values are approximate and chosen to show the arithmetic.

1. Switching electricity: a household uses 3,500 kWh a year. From coal at about 0.9 kg of CO₂ per kWh, it causes 3,500 × 0.9 = 3,150 kg. From solar with a life-cycle value of about 0.04 kg per kWh, it causes 3,500 × 0.04 = 140 kg. The saving is 3,150 − 140 = 3,010 kg, or 96%.
2. Solar farm output: a 10 MW solar farm with a capacity factor of 20% produces 10 × 0.20 × 8,760 = 17,520 MWh a year, which is enough for about 17,520,000 ÷ 3,500 = 5,000 homes.
3. Avoided emissions: if this output replaces electricity from gas at 0.4 kg per kWh, the saving is 17,520,000 × 0.4 = 7,008,000 kg, or about 7,000 tonnes of CO₂ per year.
4. Electric car: a petrol car emits 161 g/km. An electric car using 0.18 kWh/km on a grid of 0.4 kg per kWh emits 0.18 × 400 = 72 g/km. On 12,000 km per year, the saving is (161 − 72) × 12,000 = 1,068,000 g, which is about 1.07 tonnes a year.
5. Tree planting: a growing tree may absorb on the order of 20 kg of CO₂ a year (varies widely). To absorb 1 tonne (1,000 kg) takes 1,000 ÷ 20 = 50 trees for a year. To offset the 1.4 tonnes from a household’s electricity at 0.4 kg per kWh, 70 trees are required for a year, and they take decades to reach their full uptake.
6. Reaching net zero: a country emits 400 million tonnes of CO₂ a year. If it cuts 90% and removes the remaining 40 million tonnes with sinks and technology, the net is 400 × 0.10 − 40 = 0.

What is the history of climate agreements?

The UN Framework Convention on Climate Change was agreed at the Rio Earth Summit in 1992. The Kyoto Protocol of 1997 set binding targets for developed countries, and came into force in 2005. The Paris Agreement of 2015 brought almost all countries together with voluntary national pledges that are reviewed every five years. The IPCC special report of 2018 on 1.5 °C stressed the need for deep cuts by 2030. Renewable energy has expanded rapidly in the 2010s and 2020s, and electric vehicle sales have grown strongly. Even so, global emissions have not yet fallen sustainably, and the gap between pledges and the cuts needed for 1.5 °C remains large.

Which mistakes are common?

Mistake 1: Relying on planting trees alone

Trees absorb carbon slowly and can burn or be cut down. Cutting emissions from fossil fuels must come first.

Mistake 2: Thinking that renewables are the whole solution

Renewable electricity must be combined with efficiency, electrification, grids and storage, and with action on industry, transport, agriculture and land use.

Mistake 3: Confusing mitigation with adaptation

Mitigation reduces the causes of climate change. Adaptation reduces the harm from its effects. Both are needed.

Mistake 4: Treating net zero as zero emissions

Net zero allows some remaining emissions if they are balanced by removals, so the quality and permanence of removals matter.