Guide 01 · Causes
Why is the planet warming?
Short answer: we are burning coal, oil and gas, and clearing forests. That adds carbon dioxide and other heat-trapping gases to the air faster than nature can remove them, so the Earth holds on to more of the Sun's heat. Scientists call human influence on the climate "unequivocal".
The basics
A blanket that keeps getting thicker
Sunlight passes through the air and warms the ground and oceans. The warm Earth then gives off heat as invisible infrared radiation.
Some gases, mainly water vapour, carbon dioxide, methane and nitrous oxide, absorb that infrared and send part of it back down. Without them the Earth would average about −18°C instead of +15°C. That natural greenhouse effect is what makes the planet liveable.
The problem is the extra. Since the 1750s we have added enough CO₂ to raise its level by more than half, so more heat is held in each year than escapes. That surplus is warming the oceans, land and air.
What's in the air
Heat-trapping gases at record highs
Measured directly at remote observatories and averaged over the globe. All three are far above anything in the 800,000-year ice-core record.
CO₂ at Mauna Loa since 1958
Full chartShow the data as a table
| Year | Average CO₂ (ppm) |
|---|---|
| 2025 | 427.35 |
| 2024 | 424.60 |
| 2023 | 421.08 |
| 2022 | 418.53 |
| 2021 | 416.41 |
| 2020 | 414.21 |
| 2019 | 411.65 |
| 2018 | 408.72 |
| 2017 | 406.76 |
| 2016 | 404.41 |
| 2015 | 401.01 |
| 2014 | 398.81 |
| 2013 | 396.74 |
| 2012 | 394.06 |
| 2011 | 391.85 |
| 2010 | 390.10 |
| 2009 | 387.64 |
| 2008 | 385.83 |
| 2007 | 384.02 |
| 2006 | 382.09 |
Where emissions come from
Three-quarters is energy
Share of global greenhouse gas emissions by sector, in CO₂-equivalent. Energy use (for industry, buildings and transport) dominates; food and land use are the next biggest slice.
- Energy in industry 24.2%
- Energy in buildings 17.5%
- Transport 16.2%
- Other energy (leaks, unallocated fuel) 15.3%
- Agriculture, forestry & land use 18.4%
- Industrial processes (cement, chemicals) 5.2%
- Waste 3.2%
Source: Climate Watch / World Resources Institute, via Our World in Data (2016 sector breakdown)
Who emits
A handful of countries, and a long history
Today China is the largest emitter, but warming depends on the total ever emitted, where the United States and Europe lead. Per person, the picture changes again. World average: 4.7 tonnes of CO₂ per person per year.
Largest emitters, 2024
share of world CO₂Most emitted since 1850
share of all CO₂ everSource: Global Carbon Budget via Our World in Data; fossil fuels and industry, excluding land use · see every country ·
The evidence
How we know it's us, not the Sun
The physics is 160 years old
John Tyndall measured CO₂ absorbing heat in 1859, and Svante Arrhenius calculated the warming from doubling it in 1896. Modern satellites see the extra energy being trapped.
The carbon has a fingerprint
Carbon from fossil fuels has a distinct isotope signature. As CO₂ has risen, the air's carbon has shifted towards that signature, and oxygen has fallen exactly as burning would predict.
The Sun has not got brighter
Satellites show solar output flat or slightly falling since the 1980s while the planet warmed fastest. Volcanoes cause brief cooling, not decades of warming.
The pattern points to greenhouse gases
The lower atmosphere is warming while the stratosphere above cools, and nights are warming faster than days. A brighter Sun would warm everything; a thicker blanket does exactly this.
The IPCC's Sixth Assessment Report (2021) estimates humans caused about 1.07°C of warming between 1850–1900 and 2010–2019, essentially all of the observed rise.
Questions people ask
What is the main cause of climate change?
Burning fossil fuels (coal, oil and gas) for electricity, heat, transport and industry. That releases carbon dioxide, which accounts for roughly three-quarters of the warming effect of today's emissions. Deforestation, farming (mainly methane from livestock and rice) and industrial gases add the rest.
How does the greenhouse effect work?
Sunlight warms the Earth, and the Earth sheds that heat as infrared radiation. Greenhouse gases such as CO₂, methane and water vapour absorb some of that infrared and send it back down, keeping the surface warmer. Adding more of them thickens that blanket, so more heat stays in.
Could the Sun or natural cycles be causing it?
No. Satellites show the Sun's output has been flat or slightly falling since the 1980s while temperatures climbed. The upper atmosphere is cooling while the lower atmosphere warms, the fingerprint of greenhouse gases rather than a brighter Sun.
Which country emits the most CO₂?
China emits the most each year, about a third of the world total, followed by the United States and India. Over history the United States has emitted the most in total. Per person, many oil-producing states and the US, Canada and Australia are highest. See every country.
Why does methane matter if there is less of it?
Methane traps about 80 times more heat than CO₂ over 20 years, though it breaks down in about a decade. That makes cutting it (from oil and gas leaks, livestock, landfills and rice) one of the fastest ways to slow warming in the near term.