# Greenhouse gas emissions

Greenhouse gas emissions are releases of gases that absorb and emit infrared radiation, warming the lower atmosphere; the term usually refers to the anthropogenic (human-caused) emissions of carbon dioxide, methane, nitrous oxide, and fluorinated gases that drive modern climate change.<sup>[1](https://www.ipcc.ch/report/ar6/wg3/chapter/chapter-2/)</sup> [Greenhouse](https://www.edgepedia.org/greenhouse) gases are defined by their ability to absorb and emit radiation at specific wavelengths within the spectrum emitted by Earth's surface, atmosphere, and clouds; water vapor, carbon dioxide (CO₂), nitrous oxide (N₂O), methane (CH₄), and ozone are the primary natural ones, while sulfur hexafluoride (SF₆), hydrofluorocarbons (HFCs), chlorofluorocarbons (CFCs), and perfluorocarbons (PFCs) are human-made.<sup>[2](https://www.ipcc.ch/report/ar6/wg2/chapter/annex-ii/)</sup>

| Key fact | Detail |
|---|---|
| Global total | 59 ± 6.6 GtCO₂-eq of anthropogenic emissions in 2019; the 2010–2019 decade average (56 ± 6.0 GtCO₂-eq) was the highest on record<sup>[1](https://www.ipcc.ch/report/ar6/wg3/chapter/chapter-2/)</sup> |
| Gas mix (2019) | CO₂ from fossil fuels and industry 38 ± 3.0 Gt; CO₂ from land use 6.6 ± 4.6 Gt; methane 11 ± 3.2; nitrous oxide 2.7 ± 1.6; fluorinated gases 1.4 ± 0.41 GtCO₂-eq<sup>[1](https://www.ipcc.ch/report/ar6/wg3/chapter/chapter-2/)</sup> |
| Sector shares | Energy use 73.2%, agriculture, forestry, and land use 18.4%, direct industrial processes 5.2%, waste 3.2% (2016 breakdown)<sup>[3](https://ourworldindata.org/ghg-emissions-by-sector)</sup> |
| Atmospheric levels (2024) | CO₂ 423.9 ± 0.2 ppm, CH₄ 1942 ± 2 ppb, N₂O 338.0 ± 0.1 ppb, all unprecedented highs<sup>[4](https://wmo.int/files/greenhouse-gas-bulletin-no-21)</sup> |
| Fossil CO₂ trend | 2025 fossil emissions projected up 1.1% to a record 42.2 billion tonnes CO₂<sup>[5](https://www.csiro.au/en/research/environmental-impacts/emissions/Global-greenhouse-gas-budgets/Global-carbon-budget)</sup> |
| Warming outlook | Full implementation of current national pledges gives 2.3–2.5 °C of warming this century; current policies give 2.8 °C<sup>[6](https://www.unep.org/resources/emissions-gap-report-2025)</sup> |
| Required cuts | Annual emissions must fall 35% (2 °C pathway) and 55% (1.5 °C pathway) below 2019 levels by 2035<sup>[6](https://www.unep.org/resources/emissions-gap-report-2025)</sup> |

## The gases and how they are counted

Emissions of different gases are aggregated using the global warming potential (GWP), a metric that expresses the warming effect of a gas relative to CO₂ over a chosen time horizon, usually 100 years. Multiplying each gas's mass by its GWP₁₀₀ yields CO₂-equivalent (CO₂-eq) emissions, the unit in which national and global totals are reported.<sup>[3](https://ourworldindata.org/ghg-emissions-by-sector)</sup> Parties to the [Paris Agreement](https://www.edgepedia.org/paris-agreement) must use 100-year GWP values from an IPCC assessment report when reporting aggregate emissions in CO₂ equivalents.<sup>[7](https://unfccc.int/es/node/631759)</sup>

CO₂ dominates the total because most emissions take the form of CO₂ from industry and energy, and it makes the largest contribution to global GHG emissions; methane is the second biggest contributor to global warming.<sup>[8](https://www.ipcc.ch/report/ar6/wg3/downloads/report/IPCC_AR6_WGIII_SummaryVolume.pdf)</sup> Growth rates differ sharply by gas: since 1990, CO₂ from fossil fuels and industry grew 67%, methane 29%, nitrous oxide 33%, and fluorinated gases about 254%, though the F-gas increase started from very low levels.<sup>[1](https://www.ipcc.ch/report/ar6/wg3/chapter/chapter-2/)</sup>

## Where emissions come from

Almost three-quarters of global emissions come from energy use. Within that, energy use in industry accounts for 24.2% (iron and steel alone 7.2%), transport 16.2% (road transport 11.9%, aviation 1.9%, shipping 1.7%), and buildings 17.5%.<sup>[3](https://ourworldindata.org/ghg-emissions-by-sector)</sup> [Agriculture](https://www.edgepedia.org/agriculture), forestry, and land use directly account for 18.4%, with livestock and manure (5.8%), agricultural soils (4.1%), and crop burning (3.5%) among the largest components; the food system as a whole, including processing, packaging, transport, and retail, accounts for around one quarter of emissions.<sup>[3](https://ourworldindata.org/ghg-emissions-by-sector)</sup> Direct industrial processes add 5.2%, including about 3% from cement, where CO₂ is a byproduct of converting limestone to lime, and waste adds 3.2%, mainly methane from landfills and wastewater.<sup>[3](https://ourworldindata.org/ghg-emissions-by-sector)</sup>

## How emissions are measured and tracked

Measurement rests on two complementary approaches. Bottom-up inventories estimate emissions from activity data and emission factors; top-down methods infer emissions from atmospheric concentration measurements. The longest continuous atmospheric record is the [Keeling Curve](https://www.edgepedia.org/keeling-curve), measurements of CO₂ at the [Mauna Loa Observatory](https://www.edgepedia.org/mauna-loa-observatory) in Hawaii begun in 1958, when the first day of operation recorded 313 ppm; the rise since then shows a remarkably constant relationship with fossil-fuel burning, well accounted for by the premise that 57% of fossil-fuel emissions remain airborne.<sup>[9](https://keelingcurve.ucsd.edu/2013/04/03/the-history-of-the-keeling-curve/)</sup>

Reporting is institutionalized through the UN climate regime. Under the Convention and [Kyoto Protocol](https://www.edgepedia.org/kyoto-protocol), a measurement, reporting, and verification (MRV) framework defines national reporting; under the Paris Agreement, the Enhanced Transparency Framework requires all Parties to submit biennial transparency reports including national inventory reports, which undergo technical expert review.<sup>[10](https://www.unfccc.int/reporting-and-review)</sup> Annex I Parties submit annual inventories; between 1990 and 2023 their aggregate emissions without land use, land-use change, and forestry (LULUCF) fell by 30.6%.<sup>[11](https://unfccc.int/sites/default/files/resource/sbi2025_20_adv.pdf)</sup>

**Independent verification increasingly uses satellites.** A global inversion of TROPOMI satellite observations of methane found 2023 anthropogenic emissions 15% higher than UNFCCC reporting overall, and 32% higher for the oil and gas sector, with national emissions more than 50% above reported values for a quarter of countries.<sup>[12](https://www.nature.com/articles/s41467-025-67122-8)</sup> The Climate TRACE coalition, which uses satellite data and machine learning to estimate emissions at facility level, reported that global GHG emissions rose 0.50% in 2025 to a new high of 60.63 billion tonnes CO₂e, with methane setting an annual record of 412.59 Mt.<sup>[13](https://climatetrace.org/news/climate-trace-data-show-global-greenhouse-gas-emissions-hit-a-new-record-high-in-2025)</sup>

## Accounting problems

Emissions numbers depend on accounting conventions, and different conventions give different answers. National greenhouse gas inventories and scientific assessments follow different rules for land-based carbon fluxes: national inventories count all fluxes on managed land as anthropogenic and incorporate a broader scope of removals, so they report the land sector collectively as a net sink, while scientific bookkeeping models treat it as a net source. The gap between the two conventions is approximately 5.5–6.7 Gt CO₂ per year, large enough to shift global mitigation benchmarks and complicate the comparison of national pledges against modeled pathways.<sup>[14](https://www.nature.com/articles/s41586-023-06724-y)</sup> Sector-specific undercounting is also documented: national inventories systematically undercount methane and nitrous oxide from wastewater, with emissions for 38 studied countries 19–27% higher than officially reported.<sup>[15](https://www.nature.com/articles/s41558-026-02555-7)</sup>

## Trends and the emissions gap

Global emissions have continued to rise since the Paris Agreement was adopted. Fossil CO₂ emissions, including cement, are projected to grow 1.1% in 2025 to a record 42.2 billion tonnes, and CO₂ from fossil fuels and land use combined has grown 9.8% since 2015.<sup>[5](https://www.csiro.au/en/research/environmental-impacts/emissions/Global-greenhouse-gas-budgets/Global-carbon-budget)</sup> Atmospheric concentrations reflect this: the globally averaged CO₂ level reached 425.6 ± 0.1 ppm in 2025, a 53% increase above the preindustrial level of about 278 ppm, and fossil fuel emissions in 2025 were estimated at 10.3 ± 0.5 petagrams of carbon per year, more than three times the 3.0 ± 0.2 petagrams per year of the 1960s.<sup>[16](https://www.ncei.noaa.gov/bams-state-of-climate)</sup>

UNEP's [Emissions Gap Report](https://www.edgepedia.org/emissions-gap-report) 2025 quantifies how far current trajectories sit from the Paris goals. Projections based on full implementation of [Nationally Determined Contributions](https://www.edgepedia.org/nationally-determined-contributions) now give 2.3–2.5 °C of warming this century, and current policies give 2.8 °C, compared with 2.6–2.8 °C and 3.1 °C in the previous year's report; methodological updates account for 0.1 °C of the improvement, and the upcoming US withdrawal from the Paris Agreement cancels another 0.1 °C.<sup>[6](https://www.unep.org/resources/emissions-gap-report-2025)</sup> Meeting the 2 °C and 1.5 °C pathways requires cuts of 35% and 55% below 2019 levels by 2035, and the report judges that a higher exceedance of 1.5 °C will very likely happen within the next decade, with the overshoot needing to be limited through faster and larger emission reductions.<sup>[6](https://www.unep.org/resources/emissions-gap-report-2025)</sup>

## References

1. [IPCC AR6 Working Group III, Chapter 2: Emissions Trends and Drivers](https://www.ipcc.ch/report/ar6/wg3/chapter/chapter-2/)
2. [IPCC AR6 Working Group II, Annex II: Glossary](https://www.ipcc.ch/report/ar6/wg2/chapter/annex-ii/)
3. [Hannah Ritchie (2020). Sector by sector: where do global greenhouse gas emissions come from? Our World in Data](https://ourworldindata.org/ghg-emissions-by-sector)
4. [WMO Greenhouse Gas Bulletin No. 21, 15 October 2025](https://wmo.int/files/greenhouse-gas-bulletin-no-21)
5. [Global Carbon Budget 2025, CSIRO](https://www.csiro.au/en/research/environmental-impacts/emissions/Global-greenhouse-gas-budgets/Global-carbon-budget)
6. [UNEP Emissions Gap Report 2025: Off Target](https://www.unep.org/resources/emissions-gap-report-2025)
7. [UNFCCC, National Inventory Reports under the Enhanced Transparency Framework](https://unfccc.int/es/node/631759)
8. [IPCC AR6 WGIII, Frequently Asked Questions](https://www.ipcc.ch/report/ar6/wg3/downloads/report/IPCC_AR6_WGIII_SummaryVolume.pdf)
9. [The History of the Keeling Curve, Scripps Institution of Oceanography](https://keelingcurve.ucsd.edu/2013/04/03/the-history-of-the-keeling-curve/)
10. [UNFCCC, Reporting and Review](https://www.unfccc.int/reporting-and-review)
11. [UNFCCC, National greenhouse gas inventory data for the period 1990–2023, FCCC/SBI/2025/20](https://unfccc.int/sites/default/files/resource/sbi2025_20_adv.pdf)
12. [Worldwide inference of national methane emissions by inversion of satellite observations with UNFCCC prior estimates, Nature Communications (2025)](https://www.nature.com/articles/s41467-025-67122-8)
13. [Climate TRACE Data Show Global Greenhouse Gas Emissions Hit a New Record High in 2025](https://climatetrace.org/news/climate-trace-data-show-global-greenhouse-gas-emissions-hit-a-new-record-high-in-2025)
14. [Aligning climate scenarios to emissions inventories shifts global benchmarks, Nature 624, 102–108 (2023)](https://www.nature.com/articles/s41586-023-06724-y)
15. [Inconsistent national reports undercount wastewater emissions, Nature Climate Change (2026)](https://www.nature.com/articles/s41558-026-02555-7)
16. [BAMS State of the Climate 2025, NOAA NCEI](https://www.ncei.noaa.gov/bams-state-of-climate)

---
*Topic: Encyclopedia › Physical world and mathematics › Earth sciences › Climate and weather › Climate change › Climate change science and impacts › Greenhouse effect and radiative forcing*

*Initially written Sep 17, 2026 · Reviewed: Sep 30, 2026; Oct 15, 2026 · Edited: Oct 15, 2026 · Last review: Oct 15, 2026*

*Copyright 2026 EdgeChat AI, a subsidiary of Biostate AI.*

License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license