Archive Website of the UK government

The role of humans in climate change

The world's climate varies naturally as a result of:

• the way the ocean and the atmosphere interact with each other
  
• changes in the Earth's orbit
  
• changes in energy received from the sun

However, there is now very strong evidence and almost universal agreement that significant recent global warming can’t be explained just by natural causes. The changes seen over recent years, and those predicted for the next century, are considered to be mainly the result of human behaviour.

The Intergovernmental Panel on Climate Change (IPCC) is a scientific body set up by the UN to look at climate change. It says that human activity is the main cause of the changes seen in climate during recent decades.

In the last 100 years, the Earth has warmed by 0.75 degrees Celsius. Global sea levels have gone up, glaciers and sea ice have melted, and extreme weather events, like floods and droughts, are likely to happen more often.

You can find information on climate change facts and myths on the Royal Society website.

• The Intergovernmental Panel on Climate Change Opens new window

• Read more myths and facts from the Royal Society Opens new window

The greenhouse effect

The Earth's atmosphere contains gases that trap heat near the Earth's surface. These so-called ‘greenhouse gases’ are necessary to sustain life on Earth. They let the sun’s rays enter but stop some heat from escaping to outer-space. This keeps the planet warm enough to allow life to thrive.

However, as people cause more greenhouse gases to be released into the atmosphere, the greenhouse effect becomes stronger. More heat is trapped and the Earth's climate begins to change unnaturally.

Greenhouse gases, including carbon dioxide

Greenhouse gases include water vapour, carbon dioxide and other gases like methane and nitrous oxide.

Carbon dioxide (also known as CO2) is the most important greenhouse gas after water vapour and contributes strongly to the greenhouse effect. Since the Industrial Revolution, which began in the 18th century, the amount of CO2 in the atmosphere has increased by about 40 per cent. The concentration of CO2 in the Earth's atmosphere is now higher than at any time in at least the last 800,000 years.

• The greenhouse effect: Department of energy and climate change (DECC) Opens new window

Causes of the greenhouse effect

Human activity is changing the amount of greenhouse gases in the atmosphere in three important ways.

Burning fossil fuels

When fossil fuels like coal, oil and gas are burned, they release greenhouse gases. In 2005, burning fossil fuels sent about 27 billion tonnes of carbon dioxide into the atmosphere.

People burn fossil fuels to create energy, which is used for many things including:

• heating homes and buildings
  
• growing, transporting and cooking food
  
• travelling (for example, by car, plane, bus and train)
  
• treating water to make it drinkable, heating it and piping it into homes
  
• manufacturing, using and transporting products, from clothes to fridges, from plastic bags to batteries

Deforestation

Cutting down forests faster than they are replaced (deforestation) is a major contributor to climate change. It accounts for about 20 per cent of human carbon emissions – more than the entire global transport sector produces.

Deforestation makes such a huge contribution to carbon emissions because trees absorb CO2 as they grow. The more trees that are cut down, the fewer there will be left to absorb CO2, leading to it building up in the atmosphere.

In addition, the agriculture and industry that replace the forests often cause an extra problem by producing carbon emissions of their own.

• More on deforestation from the Prince's Rainforest Project Opens new window

A growing world population

As the world’s population grows, there are more people who need food, livestock and energy. This increasing demand will lead to increasing emissions.

Sources of UK emissions

Emissions of greenhouse gases in the UK come from many sources:

• 65 per cent come from burning fuel to create energy (excluding transport)
  
• 21 per cent are from transport
  
• around 8 per cent are from agriculture – mainly nitrous oxide from nitrogen fertilisers or methane given off by animals and manure
  
• 4 per cent come from industry – for example, manufacturing goods

Your carbon footprint

About 40 per cent of emissions in the UK are caused by individuals. From home heating to drinking water and from clothes to computers – anything that needs energy to produce, transport or use will release greenhouse gases.

The biggest sources of emissions for most people are likely to be:

• using energy in the home (mainly for heating)
  
• driving
  
• air travel

The amount of emissions you’re personally responsible for is known as your carbon footprint. You can work out your carbon footprint by using the ACT ON CO2 carbon calculator.

• Calculate your carbon footprint Opens new window

What you can do

To help tackle climate change, everyone needs to try and reduce their carbon footprint.

There are many simple ways you can do this – for example, switching appliances off standby or walking short journeys instead of using the car. For simple tips on cutting your carbon footprint and saving energy, see ‘Top tips on saving energy’. For tips on living a greener life, including cutting your carbon footprint, see 'Greener living: a quick guide to what you can do'.

• Greener living: a quick guide

• Short film about home energy use and climate change

More useful links

• Simple actions to help tackle climate change

• Climate change information - Department of Energy and Climate Change (DECC) Opens new window

• Climate change explained: Energy Saving Trust interactive tool Opens new window

• Climate change science by the government's chief scientific advisor Opens new window

• Humorous short film about climate change impacting on one farmer Opens new window

• Transcript of humorous short film