The Earth's climate is constantly changing. But something very serious has started to become evident in the last couple of decades. We have realised that the earth's temperature is rising dangerously fast, and this rise is due to the activities of humans.

Climate change and global warming have now become major issues for politicians, the media and the general public because the changing climate has worrying and lasting implications for people, species and the environment we live in.

This page explains the basic science of climate change and the reason why it is such an increasingly important issue.


In the most basic terms, climate change is the heating up of the planet, affecting our weather systems, freshwater and marine ecosystems and the animals and plants that live around us.


The world is surrounded by an atmosphere. This is a layer of constantly moving gases that provides us with the air that we breathe and the water that we need to stay alive.

But the atmosphere also provides another essential service to the planet; keeping the temperature of the planet at a level which makes it possible for us to live.

When heat from the sun hits the earth most of it bounces straight back into space, but some of it is absorbed by the earth itself and some is absorbed by the gases in the atmosphere.

This stored heat is then gradually released. This is what keeps the planet at a temperature where we can all live comfortably. It also ensures that the earth's different environments – from the frozen poles to the warm temperate zones and the sweltering rainforests and deserts – stay within a fairly constant range of temperatures that keep them either frozen, warm or sweltering.


Gases that store heat in the atmosphere are called 'greenhouse gases' and are also essential to maintaining life on earth.

Almost all of the Earth's atmosphere (99%) is made up of nitrogen (about 78%) and oxygen (about 21%). While both of these gases play important roles in the vast number of processes that support life on Earth, they play almost no direct role in regulating the climate.

Those responsible are the trace gases in the remaining 1% (including carbon dioxide, methane, nitrous oxide, ozone, water vapour and halocarbons). Water vapour is actually the most plentiful greenhouse gas, but the gases that are causing serious concern are the gases that are produced by humans and our industrial modern world we have created, such as carbon dioxide. If you increase the volume of greenhouse gases in the atmosphere you increase the atmosphere's ability to trap heat.

It is the rapidly increasing levels of carbon dioxide (CO₂) that is the biggest problem. This is a mixture of carbon and oxygen. CO₂ is a greenhouse gas produced by burning fossil fuels such as coal, oil (which includes petrol, diesel and most other liquid fuels) and natural gas. Approximately 20% of global CO₂ emissions come from deforestation and agriculture also contributes a range of greenhouse gases, such as methane and nitrous oxides.

In two centuries since the UK's industrial revolution (late eighteenth century to mid-nineteenth century), the amount of CO₂ mankind has emitted has steadily grown.

It is in the last half century that humanity has been burning fossil fuel at a spectacular rate. For example, the vast majority of the world's electricity is created by burning fossil fuels and the vast majority of the world transport is powered by oil.

This means that CO₂ emissions have rocketed, and as more CO₂ pours into the atmosphere, its heat-trapping properties mean that the global temperature rises.

This doesn't mean that every day will be hotter than the last; it just means that globally, over a period of years, average temperatures are increasing.


Many of the world's scientists now agree that to avoid the worst impacts of climate change we need to make sure that average temperature rise stays well below 2°C (3.4°F) above pre-industrial temperature.

The world has already warmed by 0.7°C since pre-industrial times, and due to the time delay between the release of CO₂ into the atmosphere and its effect on temperature, we are already locked into another 0.6°C increase, so 1.3°C in total.

The 2°C threshold is based on the findings of the Intergovernmental Panel on Climate Change (IPCC) and this threshold has been accepted by many governments, including the European Union.

When temperatures exceed this 2°C rise (or 1.3°C above current average records of temperature), climate change starts to become even more dangerous.

The difficult question is at what level CO₂ concentrations in the atmosphere will have to peak - or be stabilised - to prevent 2°C being exceeded?


A level of 550 parts per million (ppm) of carbon dioxide and other greenhouse gases is very unlikely to keep us below 2°C and could even mean overshooting 4°C. At 450 ppm we have a 50/50 chance of staying below 2°C. If CO₂ and other greenhouse gas concentrations were to stabilise at 400ppm, staying below 2°C would be more likely.