Where emissions come from
Which activities put greenhouse gases into the air, and why a country's total, its per-person figure and its history tell three different stories.
CO₂-equivalent (CO₂e)
Different gases trap different amounts of heat. To add them up, scientists convert each one into the amount of CO₂ that would cause the same warming over a set period, usually 100 years. About three quarters of today's emissions are CO₂ itself; most of the rest is methane.
Over a century, one tonne of methane warms about as much as roughly 30 tonnes of CO₂. So a tonne of methane is counted as roughly 30 tonnes CO₂e.
THE BIG SLICES
Energy is most of the pie
The world emits roughly 55 to 60 billion tonnes of CO₂e a year. About three quarters comes from energy: burning coal, oil and gas for electricity, heat, transport and industry. Roughly a fifth comes from farming, forests and land: cattle and sheep, fertiliser, rice paddies and clearing forest. The small remainder is mostly chemical reactions in making cement, and rotting waste in landfills.
A diesel bus, a gas heater and a coal power plant all sit in the energy slice. A cow burping methane and a forest burned to make pasture sit in the land slice.
Check yourself
Which slice of the pie does each one belong to?
- A petrol car on the daily commute
- A herd of cattle raised for beef
- A gas-fired power plant
- Flooded rice paddies giving off methane
- Burning a forest to clear land for crops
- A steel mill burning coal for heat
Show the answer
Energy: A petrol car on the daily commute, A gas-fired power plant, A steel mill burning coal for heat
Farming, forests and land: A herd of cattle raised for beef, Flooded rice paddies giving off methane, Burning a forest to clear land for crops
Inside the energy slice
- Electricity and heat is the single biggest part, because much of the world's power still comes from coal and gas.
- Transport is roughly 15% of all emissions, and most of that is cars, vans and trucks on roads.
- Industry burns fuel for high heat: steel, cement, chemicals.
- Buildings burn gas or oil for heating and cooking, and also use electricity whose emissions happen at the power plant.
Check yourself
Nima replaces his gas stove with an electric one. 'Electric has no chimney, so my cooking is now zero-emission,' he says. What's the best reply?
- He's right: emissions only count where fuel is burned in the home
- It depends on the grid: with gas or coal power, the emissions just moved to the plant
- Electric stoves always emit more than gas stoves, so he has actually made things worse
- Cooking is too small to count, so the question doesn't matter
Show the answer
It depends on the grid: with gas or coal power, the emissions just moved to the plant
Yes. Electricity is only as clean as whatever generates it. As grids add more solar and wind, his stove gets cleaner without him doing anything.
Same data, two different questions
Total per country
Asks: which countries emit the most? Big populations and big economies top the list. China emits the most today, roughly 30% of the world's fossil CO₂.
Per person
Asks: how much does an average resident emit? Divide the total by the population. The picture changes: the average American emits far more than the average person in China, and many times more than someone in India.
World CO2 from fossil fuels ≈ 37 billion tonnes a year
World population ≈ 8 billion people
Per person = 37 ÷ 8≈ 4.6 tonnes of CO2 per person per year (world average)
Rough country averages, fossil CO2 per person:
United States about 14–15 t
European Union about 6 t
India about 2 t
many African nations well under 1 tAdd methane and the other gases and the world average rises to roughly 7 tonnes CO2e per person. All figures are rounded and shift a little every year.
Check yourself
Country A has 100 million people and emits 500 million tonnes of CO₂ a year. Country B has 10 million people and emits 150 million tonnes. Hana says A is clearly the bigger problem per person. Is she right?
- Yes, because A emits more than three times as much in total
- They're equal, because both are large emitters
- No: A is 5 tonnes per person and B is 15
- You can't compare them without knowing their history
Show the answer
No: A is 5 tonnes per person and B is 15
Right. 500 ÷ 100 = 5 and 150 ÷ 10 = 15. Totals tell you where emissions are concentrated; per-person numbers tell you about the way people live.
INSIDE A COUNTRY
Averages hide big differences
Within every country, footprints rise with income: more flights, bigger homes, more driving, more stuff. The IPCC estimates that the richest tenth of households worldwide cause roughly a third to almost half of household emissions, while the poorest half cause only about a seventh.
Two neighbours in the same city can differ several times over. One takes the metro and rarely flies; the other drives a large car daily and flies abroad a few times a year.
Check yourself
Lina lives in a country whose average footprint is below the world average, but she earns well, drives most days and flies abroad several times a year. Her own footprint is probably below the world average too.
Show the answer
False
False. A national average mixes everyone together, and footprints climb with income. Frequent flying and daily driving can put one person far above both her country's average and the world's.
TWO MORE LENSES
History and consumption
CO₂ stays in the air for centuries, so warming follows the total ever emitted, not just this year's. By that cumulative measure, the United States has emitted the most since the industrial revolution, and China is second. A second lens is consumption: counting emissions where goods are bought rather than where they're made. Rich importers look higher on that count.
A phone assembled in one country and sold in another: production accounting charges the factory's country; consumption accounting charges the buyer's.
Check yourself
Match each question to the measure that answers it
Show the answer
- Which country emits the most this year? → Total per country
- How much does a typical resident emit? → Per person
- Who caused most of the warming so far? → Cumulative emissions
- Whose shopping drives the factories? → Consumption-based emissions
Lesson recap
- CO₂e puts all greenhouse gases on one scale; CO₂ is about three quarters of the total.
- About three quarters of emissions come from energy, roughly a fifth from farming, forests and land.
- Totals, per-person figures, history and consumption answer different questions, so check which one a headline uses.
- Footprints rise with income: the richest tenth of households cause a far bigger share than the poorest half.