How do greenhouse gas emissions drive the global warming process?
Executive summary
Greenhouse gas (GHG) emissions—from CO2, methane, nitrous oxide and fluorinated gases—trap extra heat in the Earth system by increasing atmospheric concentrations and changing the planet’s energy balance, driving observed warming and record-hot years (e.g., 2024–2025) [1] [2]. Global fossil-fuel CO2 is on track to hit record highs in 2025 and the remaining carbon budget for 1.5°C is effectively exhausted (about 170 GtCO2 left — ~four years at 2025 rates), meaning continued emissions will rapidly use up what remains to avoid higher warming [3] [4] [5].
1. How greenhouse gases actually warm the planet — the physics in plain language
Greenhouse gases let sunlight reach the surface, which warms the ground and oceans; the surface then emits infrared (longwave) radiation back toward space. Higher concentrations of well-mixed GHGs absorb and re‑emit some of that infrared energy back down, reducing outgoing longwave radiation and increasing the Earth’s energy imbalance — the net extra energy retained in the climate system — which raises global temperatures and ocean heat content [2] [1].
2. Which gases matter most and why it’s not just CO2
Carbon dioxide is the dominant long-lived driver, responsible for roughly three‑quarters of GHG emissions by mass and more than half the warming influence of human-emitted gases; methane and nitrous oxide are fewer in mass but have much stronger warming potency per molecule and matter a lot for near‑term warming [6] [1]. The Annual Greenhouse Gas Index shows combined human-emitted GHG warming influence has risen markedly [7].
3. Emissions are still growing — recent trends and near‑term forecasts
Multiple 2025 assessments report fossil-fuel CO2 and aggregate GHG emissions are flat to rising, with fossil CO2 projected to reach record highs in 2025 and total GHGs around 10% above 2015/Paris levels; models project a roughly 1.1% rise in carbon emissions by end‑2025 in some analyses [3] [8] [5]. EDGAR and IEA datasets confirm fossil CO2 remains the main contributor and that global emissions continue to increase overall [9] [10].
4. Why incremental emissions matter now — the carbon budget and limits
Scientific budgets show little room remains to limit warming to 1.5°C: the Global Carbon Budget estimates about 170 billion tonnes CO2 left for 1.5°C — roughly four years of 2025 emissions — and broader budgets for 1.7–2°C would be exhausted in decades at current rates [4] [5]. UNEP warns that to keep 1.5°C within reach emissions needed to peak before 2025 and fall rapidly — cuts of roughly 43% by 2030 in some scenarios — otherwise overshoot becomes very likely [11] [12].
5. Feedbacks and amplifiers make emissions effects non‑linear
The climate response isn’t simply proportional to emissions: rising temperatures change clouds, sea‑ice extent, water vapor and the carbon sinks (land and ocean) that absorb CO2. These changes alter absorbed solar radiation and outgoing longwave radiation, amplifying warming and increasing the Earth’s energy imbalance that drives record heat in surface and ocean layers [2] [9].
6. Sector and regional drivers — where emissions come from and what shifts matter
Most CO2 stems from burning fossil fuels for energy, industry and transport (92% of CO2 from fossil fuel use in CO2 category), with land‑use change and agriculture contributing sizable methane and nitrous oxide shares; different sectors and countries drive trends, so policy and technology shifts (e.g., renewables, electric transport, reduced deforestation) can change trajectories [6] [10] [13].
7. Two competing narratives in present reporting
One narrative — emphasized by the Global Carbon Project, IEA and major outlets — is that emissions are still rising and near‑term prospects are dire, with record fossil CO2 set for 2025 and the 1.5°C budget nearly exhausted [3] [5] [4]. An alternate but not contradictory strand highlights signs of slowing growth and that emissions could peak this decade if major emitters act (some scientists say China’s pathway could determine global peak), implying policy choices still matter [8] [5].
8. Bottom line for policy and public understanding
The chain is straightforward: human emissions raise atmospheric GHG concentrations, that increases the Earth’s energy imbalance and raises temperatures — recent data show concentrations and heat are at record levels and emissions remain high, so rapid, deep cuts are required to avoid larger overshoots [1] [2] [11]. Available sources do not mention specific mitigation technologies’ costs or political feasibility beyond general recommendations and national pledges (not found in current reporting).