Which Greenhouse Gases Matter Most?

Greenhouse gases differ in two vital ways: their potency and their permanence. Some, like methane, are powerful at trapping heat but vanish from the atmosphere within a decade. Others, like CO₂, have a lower impact per ton but linger for centuries or millennia, locking in warming for generations to come.

The graph shows annual global human-induced emissions of the main greenhouse gases for 2024.¹ To compare emissions of different gases, scientists convert them into CO₂ equivalents (CO₂eq.). This is done using a metric called Global Warming Potential (GWP), which calculates how much heat a gas traps over a 100-year period compared to CO₂. For example, since methane is roughly 28 times more potent than CO₂ over a century, one ton of methane is recorded as 28 tons of CO₂eq.² Using this scale, CO₂ alone is responsible for roughly three-quarters of the total warming impact of today’s emissions.

What are the main anthropogenic greenhouse gases?

Carbon dioxide (CO₂) is the primary driver of climate change, released mainly through the burning of fossil fuels (coal, oil, and gas) and deforestation. A significant portion of CO₂ we emit today will remain in the atmosphere for centuries to millennia, gradually accumulating over time.

Methane (CH₄) is the second largest contributor to warming, arising primarily from agriculture (livestock and rice), leaky fossil fuel infrastructure, and waste decomposition. While it is about 80 times more powerful than CO₂ over a 20 year period, it breaks down in the atmosphere after only about a decade. This means that while methane causes intense short-term warming, reducing its emissions offers the fastest way to slow global warming in the near future.

Nitrous oxide (N₂O) is released mainly in agriculture due to excessive use of fertilisers rich in nitrogen. It is 273 times more powerful than CO₂ and it stays in the atmosphere for over a century. The rise of these emissions has been accelerating in recent years.

Fluorinated gases (F-gases) are man-made gases used mostly in refrigeration and air conditioning. While emitted in smaller quantities, they are “super-pollutants” – some are thousands of times more effective at trapping heat than CO₂. The emissions of F-gases have risen rapidly, but international agreements are already in place to phase down their use in favour of climate-friendly alternatives.³

A note on water vapour

It is often argued that water vapour is the most abundant greenhouse gas. While true, it is not a direct “driver” of warming caused by humans. Instead, water vapor acts as an amplifier: as CO₂ and other gases warm the air, the atmosphere holds more moisture, which then traps even more heat. This feedback loop is a well-understood part of climate modeling and is triggered by the primary human-induced gases described above.

Footnotes

1. We use data from two sources. Data on CO2 from deforestation and land use change (LULUCF) come from the 2025 Global Carbon Budget: Friedlingstein, P. et al. (in review, 2025). Global Carbon Budget 2025. Earth Syst. Sci. Data Discuss. [preprint]. DOI: 10.5194/essd-2025-659. Data on other greenhouse gases come from EDGAR 2025 dataset: EDGAR (Emissions Database for Global Atmospheric Research) Community GHG Database, a collaboration between the European Commission, Joint Research Centre (JRC), and the International Energy Agency (IEA). European Commission, JRC (Datasets). [https://edgar.jrc.ec.europa.eu/report_2025] ↩

2. The figures for global warming potential of different greenhouse gases and their lifetime in the atmosphere in this page are based on Chapter 7 of IPCC’s AR6 WGI report. Intergovernmental Panel on Climate Change. (2021). Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to AR6. DOI: 10.1017/9781009157896. ↩

3. Phasedown of Hydrofluorocarbons (HFCs) is the main goal of the so called Kigali Amendment to the Montreal Protocol, which was ratified by most countries all around the world. The status of ratification can be tracked here. ↩