The term 'climate change' usually refers to recent changes in climate that have been observed since the early 1900s.
Climate is not the same as weather
Climate refers to the average weather experienced in a region over a long period, typically 30 years. This includes temperature, wind and rainfall patterns. The climate of the Earth is not static, and has changed many times in the past - this is known as 'natural variability'.
The greenhouse effect
The earth is kept warm by the greenhouse effect. Greenhouse gases such as carbon dioxide and methane are naturally found in the atmosphere. They trap heat from the sun and keep our planet warm enough to inhabit. Without greenhouse gases the Earth would be about -18 degrees Celsius.
Human impact on climate
There is a scientific consensus that the recent observed rise in global temperature can only be explained by the rise in greenhouse gas emissions caused by human activities.
Since the industrial revolution, human activity, mostly the burning of fossil fuels, has resulted in the release of large amounts of greenhouse gases into the atmosphere. This is enhancing the greenhouse effect and pushing up global temperatures.
Average global temperatures have already risen approximately one degree Celsius since pre-industrial levels, and even if we could stop emitting all greenhouse gases tomorrow, they would continue to rise by at least a further 0.6 degrees. Limiting temperature rise to below two degrees is the internationally agreed target to avert dangerous climate change.
There are clear signs that our world is warming. We’ve had markedly higher global average temperatures over the last decade, ice sheets and glaciers are melting and average river water temperatures are increasing. Globally, the hottest ten years on record have all been since 1990, and February 2010 was warmest on record for southern hemisphere.
How will the climate change?
While a two degree rise in average global temperatures doesn’t sound very dangerous, the effects will be stark. The present one degree rise has already shown severe impacts for our polar regions and small island states. The Arctic is warming at about twice the global average and sea ice in the region has declined dramatically over the past 30 years. Antarctica is now losing around 190 billion tonnes of ice a year. Small island states, including 15 nations found in the Pacific, may face the most dire and immediate consequences. Eighty percent of the Maldives lies three feet or less above sea level and the predicted rise in sea level caused by global warming could lead to their eventual disappearance.
Impacts of further warming of four degrees or more are likely to include significant reductions in food production in some regions, hundreds of millions of people without enough water, mass species extinctions and sea levels rising by several metres.
In the UK, we will witness more extreme events, such as flooding, storms, sea level rise and drought as well as wetter warmer winters and hotter drier summers.
Why is tackling climate change so important?
Climate change will lead to major adverse impacts on people and wildlife, so we need to minimise the damage.
In the UK, there are currently 490,000 properties at significant risk of flooding. If we don’t increase action to reduce flood risk, an additional 350,000 more properties (making a total of 830,000) will be at significant risk of flooding by 2035 due to climate change.
The total annual river flow in England and Wales could drop by 10 to 15 per cent by 2050, with 80 per cent less water in some rivers during the summer months.
The overall costs and risks of climate change will be equivalent to losing at least five per cent of global GDP each year. In contrast, the cost of action - reducing greenhouse gas emissions to avoid the worst impacts of climate change - can be limited to around two per cent of global GDP each year.
What do we need to do?
It is critically important that urgent action is taken worldwide to both reduce emissions of greenhouse gases and to adapt to the unavoidable changes.