Climate change mitigation

• 1. Introduction

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  Climate change mitigation is the project of pulling humanity back from a trajectory it has already set in motion. Global greenhouse gas emissions averaged a record 56 billion tonnes a year in the 2010s, and the atmosphere now holds about 50% more carbon dioxide than it did before industrialisation. The 2015 Paris Agreement asked the world to stay below 2 degrees Celsius of warming. Current national policies, by the best available assessments, are pointed at roughly 2.7 degrees by the end of the century. The gap between where we are headed and where we need to go is the subject of this documentary. How do you cut emissions nearly in half within a decade? Which strategies are already working, and which remain aspirational? And what stands between the pledges countries have made and the transformations those pledges actually require?

• 2. The Emissions Picture

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  In 2016, energy for electricity, heat, and transport was responsible for 73.2% of all greenhouse gas emissions. Coal-fired power stations alone accounted for 20% of global greenhouse gas emissions, making them the single largest source. Direct industrial processes added another 5.2%, waste contributed 3.2%, and agriculture, forestry, and land use made up 18.4%. Livestock and manure together produce 5.8% of all greenhouse gas emissions. Methane is a particularly urgent target because, unlike carbon dioxide, it is short-lived; it persists in the atmosphere for days to 15 years, meaning that cutting it yields faster results. Carbon dioxide, by contrast, can remain in the atmosphere for millennia. The Kigali Amendment, ratified by many countries, created a political mechanism to address fluorinated gases from refrigerants, one area where an international agreement has already shifted the trajectory. Scientists have expanded their ability to track all of this by increasing reliance on satellites to locate and measure emissions and deforestation, moving beyond the estimated figures and governments' self-reported data that researchers once had to rely on.

• 3. Solar, Wind, and the Grid

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  A 2024 review found that the global levelized cost of electricity for solar photovoltaics had fallen to between US$0.039 and 0.041 per kilowatt-hour. That figure matters because solar PV has now become the cheapest way to generate electricity in many parts of the world. The IPCC estimates that solar and wind together have the largest potential to reduce emissions before 2030 at low cost compared to other options. The growth of photovoltaics has followed a near-exponential path, roughly doubling every three years since the 1990s. Wind and solar are also complementary in ways that soften their individual variability: in most regions, wind generation is higher in winter when solar output is low, and there is more wind at night when solar panels produce nothing. Linking different geographic regions through long-distance transmission lines allows excess generation in one area to cover shortfalls in another. Energy storage is a further tool; pumped-storage hydroelectricity remains the most widely used method, though batteries serve well for shorter storage periods. The deployment of renewable energy needs to accelerate six-fold, from 0.25% annual growth in 2015 to 1.5%, in order to keep global warming under 2 degrees Celsius.

• 4. Forests, Soils, and Wetlands

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  About 95% of deforestation occurs in the tropics, where clearing land for agriculture is one of the main drivers. The Stern Review, published in 2007, stated that curbing deforestation was among the most cost-effective ways to reduce greenhouse gas emissions. Reforestation could save at least 1 gigatonne of carbon dioxide per year at an estimated cost of $5-15 per tonne. Restoring all degraded forests globally could capture about 205 gigatonnes of carbon. Peatlands cover just 3% of the land's surface, yet store up to 550 gigatonnes of carbon, representing 42% of all soil carbon and exceeding the carbon stored in all other vegetation types including the world's forests. Coastal wetlands tell a similarly striking story: mangroves, salt marshes, and seagrasses store carbon 40 times faster than tropical forests, despite equalling only 0.05% of the plant biomass on land. In Niger and Mali, legal reforms giving local communities ownership over trees have driven what scientists describe as the largest positive environmental transformation in Africa. From space, the contrast between Niger's recovering landscape and the more barren land in Nigeria, where the law has not changed, is visible. Globally, protecting healthy soils and restoring the soil carbon sponge could remove 7.6 billion tonnes of carbon dioxide from the atmosphere each year, more than the annual emissions of the United States.

• 5. Transport and Buildings

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  Transportation accounts for 15% of emissions worldwide. Aviation presents a particular challenge: in 2018, global commercial aviation generated 2.4% of all carbon dioxide emissions, and by 2020 those emissions were 70% higher than in 2005. By 2050, they could grow by 300%. Battery-powered aircraft are likely to enter the market only after 2035; hybrid-driven aircraft are expected to start commercial regional flights after 2030. Shipping faces its own difficult transition. Maersk, the world's largest container shipping line, has warned of stranded assets when investing in transitional fuels like liquefied natural gas, and lists green ammonia among its preferred fuels for the future. Buildings account for 23% of global energy-related emissions, with about half of that energy going to space and water heating. Of the 2.8 billion people living in the hottest parts of the world, only 8% currently have air conditioners, compared with 90% in the United States and Japan. By combining energy efficiency improvements with a transition away from fluorinated refrigerants, the world could avoid cumulative greenhouse gas emissions of between 210 and 460 gigatonnes over the next four decades.

• 6. Diet, Demand, and Behaviour

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  Food accounts for nearly 20% of the global carbon footprint. Almost 15% of all anthropogenic greenhouse gas emissions have been attributed to the livestock sector. In Brazil, producing one kilogram of beef can result in up to 335 kg of carbon dioxide equivalent emissions when rainforest is cleared for grazing. Widespread adoption of a vegetarian diet could cut food-related greenhouse gas emissions by 63% by 2050, according to estimates in the source. China introduced new dietary guidelines in 2016 aiming to cut meat consumption by 50% and reduce greenhouse gas emissions by 1 gigatonne per year by 2030. The richest 10% of people globally emit about half of all lifestyle emissions. A 2024 paper in Environmental Research Letters described how behavioural, social, and infrastructural interventions, including shifting consumption patterns and promoting shared mobility, could collectively reduce global greenhouse gas emissions by 40-70% by mid-century. A companion 2024 article in Nature Climate Change identified six key recommendations for integrating behavioural science into mitigation strategies, including overcoming barriers to research, fostering cross-disciplinary collaboration, and promoting practical behaviour-oriented solutions. If high-income nations switched to plant-based diets and freed land used for animal agriculture, that land could sequester 100 billion tonnes of carbon dioxide by the end of the century.

• 7. Carbon Removal and Capture

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  Biochar supplied 94% of all durable carbon dioxide removal credits delivered in 2023, making it the most commercially scaled removal technology available today. Expert assessments place the net cost of removing carbon dioxide with biochar at between US$30 and $120 per tonne, and studies indicate the carbon it contains remains stable in soils for centuries. Enhanced weathering, which involves spreading finely ground silicate rock such as basalt onto surfaces to accelerate natural chemical reactions, could remove 2-4 gigatonnes per year at costs estimated in the US$50-200 range per tonne. Ocean-based methods could remove between 1 and 100 gigatonnes per year, with costs in the order of US$40-500 per tonne. Stratospheric aerosol injection could reduce global temperatures quickly by dispersing sulfate aerosols in the stratosphere, but deployment at climatically relevant scale would require designing and certifying a new fleet of high-altitude aircraft, a process estimated to take a decade or more, with ongoing operating costs of about US$18 billion for each degree Celsius of cooling. Risks include ozone depletion, altered regional precipitation, and a sudden warming rebound if the programme were ever interrupted. The IPCC estimates that the costs of halting global warming would double without carbon capture and storage. Bioenergy with carbon capture and storage was capturing approximately 2 million tonnes per year as of the reporting period, with scientific estimates of its potential reaching up to 22 gigatonnes per year.

• 8. Policy, Costs, and What Comes Next

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  An evaluation of 1,500 climate policy interventions carried out between 1998 and 2022, spanning 41 countries across 6 continents that together accounted for 81% of global emissions, found only 63 successful interventions that achieved significant emission reductions. The total emissions averted by all 63 combined was between 0.6 and 1.8 billion metric tonnes per year. The Paris Agreement requires 23 billion metric tonnes of reductions per year. Carbon pricing was found to be most effective in developed countries, while regulation proved more effective in developing countries. In 2021, more than 21% of global greenhouse gas emissions were covered by a carbon price, largely because of the launch of the Chinese national carbon trading scheme. The International Monetary Fund estimated fossil fuel subsidies at more than $5 trillion per year, a figure that dwarfs the 1-2% of GDP economists estimate mitigation would cost. The Stern Review calculated that inaction could cost at least 5% of global GDP annually, and potentially 20% or more when broader risks are included. The European Commission forecasts a shortage of 180,000 skilled workers in hydrogen production and 66,000 in solar photovoltaic power by 2030, a concrete signal of how quickly the energy transition is creating demand that existing training pipelines cannot yet fill.