Global Warming

Global warming is the long-term rise in Earth's average surface temperature, driven mainly by greenhouse gases released by human activity. People sometimes use "global warming" and "climate change" to mean the same thing, but there is a subtle difference. Global warming specifically describes the rise in temperature. Climate change covers all the wider effects, like changes in rainfall, sea level, storm patterns and seasons. Global warming is one of the biggest challenges humans have ever faced, but the good news is we know what is causing it, and we know how to stop it.

Average warming since 1750Around 1.2 CMostly since 1980
Pace today0.18 C per decadeAccelerating
Main causeBurning fossil fuelsCoal, oil and gas
Sea level riseAbout 3.4 mm/yearAnd speeding up
Hottest year on record2024Or in many regions, even hotter again
Paris Agreement targetBelow 1.5 C ideallyBelow 2 C as a backstop

What is global warming?

Global warming is the steady increase in the average temperature of the air at Earth's surface, the oceans, and the lower atmosphere. The Earth has warmed by about 1.2 degrees Celsius since the late 1800s, and most of that warming has happened since 1980. Every recent decade has been warmer than the one before, and the last 10 years are the 10 hottest ever measured.

Why is the Earth warming?

Earth's temperature is set by a balance between two things:

The amount of sunlight reaching the planet (energy in).
The amount of heat escaping back into space (energy out).

Greenhouse gases in the atmosphere (carbon dioxide, methane and others) make it harder for heat to escape, like a blanket trapping warmth. Some greenhouse effect is natural and necessary: without it, Earth would be a frozen rock at about -18 degrees Celsius. The problem is that humans are adding extra greenhouse gases on top of the natural amount, making the blanket thicker and trapping more heat than is normal.

The biggest source of extra greenhouse gases is burning fossil fuels (coal, oil and natural gas) for electricity, transport, heating and industry. Deforestation also matters: cutting trees releases the CO2 they stored and means less is absorbed each year.

Fact A typical petrol car releases about 4-5 tonnes of CO2 per year. A short-haul flight from London to Spain adds another 0.5 tonnes per passenger. A whole UK household, including electricity, heating, food and transport, averages around 10 tonnes of CO2 per year. To meet net-zero, that needs to drop close to zero by 2050.

The greenhouse gases

Carbon dioxide (CO2): the main one. Lasts hundreds of years in the atmosphere. From cars, power stations, factories, cement and deforestation.
Methane (CH4): stronger but shorter-lived (about 12 years). From cattle, rice paddies, landfills and natural gas leaks.
Nitrous oxide (N2O): from farming fertilisers.
Water vapour: actually the biggest natural greenhouse gas, but its level depends on temperature. Adds to the warming caused by the others.
F-gases: from refrigerators, air conditioning and aerosols. Tiny amounts but very strong per molecule.

What global warming is doing

Some of the changes already visible around the world:

Glaciers retreating in the Alps, Andes, Himalayas and Rocky Mountains.
Arctic sea ice has shrunk by about 40% in summer since 1979.
Greenland is losing 270 billion tonnes of ice per year.
Sea levels have risen by about 20 cm since 1900 and are rising about 3.4 mm per year now.
Heatwaves are more frequent and intense. Summer 2022 broke European records.
Wildfires are getting bigger and lasting longer in places like Australia, California and Greece.
Ocean acidification is bleaching coral reefs. The Great Barrier Reef has lost about half its coral cover since 1995.
Some species are moving towards the poles or up mountains to find cooler temperatures.
Spring is arriving earlier, autumn later, in many places.

What scientists predict

If we continue with very high emissions, scientists predict Earth could warm by 3 to 5 degrees Celsius by 2100. That would cause serious harm: large parts of the world becoming too hot for outdoor work, major coastal cities flooded, hundreds of millions of climate refugees, mass extinctions in nature and food shortages.

If we cut emissions hard, warming might be kept to around 1.5 to 2 degrees, the target set by the Paris Agreement. Damage would still be significant, but the worst impacts could be avoided. Every fraction of a degree we save matters.

Did you know? Mars almost certainly had liquid water on its surface billions of years ago, possibly even oceans. Then, because the planet is smaller and lost its magnetic field, the atmosphere was stripped away by the solar wind. Mars is now a freezing, almost-airless world. Earth has been lucky to keep its atmosphere stable for billions of years, the very thing we are now changing in our own time.

How to stop global warming

The recipe is well understood. We need to:

Switch electricity generation to renewables (wind, solar, hydro) and low-carbon nuclear.
Electrify almost everything that currently burns fuel: cars (now electric), heating (heat pumps), industry (electric processes).
Make buildings more efficient through insulation and better appliances.
Eat less meat and dairy (especially beef and lamb).
Stop deforestation and plant new forests where possible.
Develop new technology to capture CO2 from the air or from factory chimneys.
Help poorer countries leapfrog dirty technology straight to clean ones.

What can kids do?

Save energy at home: turn off lights, use less hot water, wear extra jumpers in winter.
Walk or cycle instead of asking for car rides.
Eat plant-based meals a few times a week.
Recycle and avoid waste.
Plant a tree in your garden, school or local park.
Learn the science and share it: every conversation helps.
Ask your school what its climate plan is.
Take part in events like Earth Day on 22 April.

Try this Make a "carbon detective" tour of your house. Walk around with a notebook and list everything that uses energy: lights, heating, TV, computers, fridge, washing machine, oven, kettle. Tick the things that are needed right now and the things that could be switched off. Switching off the unused ones is the single easiest thing your family can do to cut emissions. Many homes can save 10 to 20% of their electricity just from "phantom loads" (devices left on standby).

Deeper dive: how do we know it is us causing it?

Climate has changed many times naturally in Earth's past, due to volcanic eruptions, asteroid impacts, changes in the Sun and slow wobbles in Earth's orbit. So how can scientists be so sure that today's warming is caused by humans?

The evidence is overwhelming, and comes from several independent lines:

Carbon's fingerprint: CO2 from burning fossil fuels has a slightly different mix of carbon isotopes from CO2 from other sources. The extra CO2 in the atmosphere matches the fossil fuel fingerprint exactly.
Timing matches: the rise in CO2 began at exactly the moment humans started burning coal and oil in industrial quantities (1750-1850), and accelerated after 1950 as the world industrialised.
The Sun is not the cause: solar output has actually fallen slightly over the past 40 years. If the warming were natural, it should have cooled.
Pattern matches predictions: scientists predicted decades ago that human-caused warming would warm nights faster than days, winters faster than summers, the lower atmosphere while cooling the upper. All those patterns have been confirmed.
Computer models: when you run climate models with natural causes only, they cannot reproduce the warming since 1980. Add in human emissions and the models match the observations exactly.
Scientific agreement: more than 97% of climate scientists who actively publish in the field agree that human-caused warming is real.

This level of agreement and evidence is unusual in science. It is similar to the level of confidence we have that smoking causes cancer or that evolution is real. The science of human-caused warming is no longer in doubt; the question now is what to do about it.

For more, see climate change and renewable vs non-renewable energy.