Greenhouse gas emissions

• 1. Introduction

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  Greenhouse gas emissions from human activities have now pushed atmospheric carbon dioxide to nearly 50% above pre-industrial levels. That single number sits at the center of one of the most consequential stories of the industrial age. How did humans manage to alter the composition of the atmosphere so dramatically? Which gases are driving the change? Who is responsible, and how unevenly is that responsibility distributed? This documentary traces the sources, the measurements, the inequities, and the scale of a problem that by 2025 had reached a record high of over 60 billion tonnes in a single year.

• 2. Gases Behind the Warming

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  Carbon dioxide from burning fossil fuels is the dominant driver, accounting for more than half of warming. Burning oil, coal, and gas alone was estimated to have emitted 37.4 billion tonnes of CO2-equivalent in 2023. Coal-fired power stations stand out as the single largest individual source, responsible for over 20% of global greenhouse gas emissions as of 2018. Methane tells a subtler story. With a five-year global warming potential of up to 100 times that of CO2, the current 389 million tonnes of methane in annual emissions carries roughly the same short-term warming punch as carbon dioxide itself. A reduction of about 30% below current methane levels would be enough to stabilize its atmospheric concentration. Nitrous oxide has a global warming potential over 100 years estimated at 265 times greater than CO2, and more than 50% reductions would be needed just to stabilize it. Fluorinated gases, including hydrofluorocarbons and sulfur hexafluoride, contribute less in volume but carry extreme warming potency and persist in the atmosphere for long periods. One regulatory footnote worth knowing: CFCs are also greenhouse gases, but they were regulated under the Montreal Protocol primarily because of ozone depletion. In 2016, negotiators from over 170 nations extended that framework through the Kigali Amendment, reaching a legally binding accord to phase out hydrofluorocarbons. The phase-down of less active HCFC compounds is due to be completed in 2030.

• 3. Where Emissions Come From

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  Energy is the dominant sector overall, responsible for around 73% of total greenhouse gas emissions. Within that, electricity generation powered by fossil fuels accounts for roughly a quarter of all global emissions when measured at the point of production. A striking detail from a survey of fossil-fuel power plants across 221 countries: just 5% of the world's power plants are responsible for almost three-quarters of carbon emissions from electricity generation. Transportation accounts for 15% of worldwide emissions, and road freight alone contributes over a quarter of global transport emissions. Aviation generated 2.4% of all CO2 emissions from global commercial operations in 2018, and by 2020 the aviation sector's total climate impact had doubled over the preceding two decades. Agriculture carries its own distinct weight. The largest source of anthropogenic methane is agriculture, with livestock leading the way. Cattle alone account for about 65% of the livestock sector's methane emissions, serving as sources whether raised for beef, dairy, or other purposes. Nitrous oxide from agricultural soils is largely tied to fertilizer application, and 56% of all nitrous oxide emissions trace back to agriculture, especially meat production. Buildings represent another underappreciated source. In 2019, the building sector was responsible for 12 gigatonnes of CO2-equivalent, with over 95% of that being carbon dioxide. Nearly half of building sector emissions come from producing electricity for use inside buildings. A 2022 study found that across bulk material sectors including steel, aluminum, cement, and paper, total emissions reached approximately 8.4 billion tonnes of CO2-equivalent. The world's single largest individual industrial emitter is Secunda CTL, releasing 56.5 million tonnes a year.

• 4. The Inequality of Emissions

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  China is the world's largest annual emitter by a significant margin, releasing around 10 billion tonnes each year, more than one-quarter of global emissions. In 2024, China, India, Russia, and Indonesia all increased their emissions compared to 2023, with Indonesia seeing the largest relative increase and India posting the largest absolute increase at 164.8 million tonnes of CO2-equivalent. The European Union moved in the opposite direction. EU-27 emissions excluding land use change were approximately 35% lower in 2024 than in 1990, reaching 3.2 gigatonnes of CO2-equivalent. The per-capita divide is stark. The current global average is 4.9 tonnes of CO2-equivalent per person per year. That is more than twice the 2.3 tonnes estimated to be compatible with limiting warming to 1.5 degrees Celsius by 2030 under the Paris Agreement. Annual per capita emissions in industrialized countries are typically as much as ten times the average in developing countries. The divide runs even deeper when traced to wealth rather than geography. A 2020 report by Oxfam and the Stockholm Environment Institute found that the richest 1% of the global population caused twice as much carbon emissions as the poorest 50% over the 25 years from 1990 to 2015, representing 15% of cumulative emissions versus 7%. The wealthiest 5% of the global population was responsible for 37% of the absolute increase in global emissions over that same period. In transport, the disproportion is particularly sharp: the top 10% of earners consume 56% of vehicle fuel and make 70% of vehicle purchases. Africa and South America each account for only 3-4% of global emissions, roughly equal to the combined emissions of international aviation and shipping.

• 5. Measuring and Accounting

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  Total cumulative emissions from 1870 to 2022 were 703 gigatonnes of carbon, of which fossil fuels and industry contributed 484 gigatonnes and land use change contributed 219 gigatonnes. Land use change, primarily deforestation, caused about 31% of cumulative emissions over that period; coal 32%, oil 24%, and gas 10%. Carbon dioxide stays in the atmosphere for at least 150 years and up to 1,000 years. Methane disappears within about a decade, and nitrous oxides last roughly 100 years. These differences in atmospheric lifetime are why calculations of warming potential must be regularly updated. Measuring emissions is not as straightforward as it sounds. Four main methods exist: the emission factor-based method, mass balance method, predictive emissions monitoring systems, and continuous emissions monitoring systems. They differ in accuracy, cost, and usability. There is also a fundamental boundary question: should emissions be assigned to the country where they are produced, or to the country whose consumers demanded the goods that created them? Under a production-based framework, China and other emerging markets appear as large exporters of emissions. Under a consumption-based framework, the US, Japan, and Western Europe absorb a greater share. A 2017 survey found that 100 companies were responsible for 71% of global direct and indirect emissions, and that state-owned companies accounted for 59% of their share. The national accounts balance approach tracks the difference between emissions embedded in a country's exports and imports. For many wealthier nations, that balance is negative, reflecting their dependence on imported goods produced elsewhere. The sharp acceleration in emissions after 2000, reaching more than 3% annual growth versus 1.1% per year during the 1990s, was largely driven by China and by the reversal of declining carbon intensity trends in both developed and developing economies.

• 6. Historical Weight and Future Trajectory

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  Humans have now emitted more greenhouse gases in total than the Chicxulub meteorite impact that caused the extinction of the dinosaurs. Industrial activity powered by fossil fuels began significantly raising greenhouse gas concentrations starting around 1750. Emissions then accelerated rapidly from around 1950, driven by population growth and economic expansion following World War II. In 1997, human-caused Indonesian peat fires alone were estimated to have released between 13% and 40% of the average annual global carbon emissions from fossil fuels in a single year. Annual carbon emissions from tropical deforestation doubled over the two decades from 2001 to 2019, rising from 0.97 petagrammes of carbon per year to 1.99 petagrammes per year. The COVID-19 pandemic briefly interrupted the trend. Global carbon dioxide emissions fell by 6.4% in 2020, a drop of 2.3 billion tonnes. In April 2020 alone, emissions fell by up to 30%. But the rebound was swift. Emissions recovered as restrictions lifted, and the long-term impact of pandemic policies was negligible. In October 2023, the US Energy Information Administration released projections through 2050 using a range of scenarios. In no scenario did aggregate energy-related carbon emissions dip below 2022 levels, even when varying GDP growth, technological learning rates, and oil prices. Meanwhile, deforestation continues to drive land use emissions, and a growing concern for electricity usage is the expansion of artificial intelligence, which is projected to significantly increase global energy demand in the years ahead. The plastics sector alone, on current trends, is projected to contribute 1.34 billion tonnes of lifecycle greenhouse gas emissions annually by 2030.