What is climate change?
The Earth's climate naturally changes over long time periods. Over the 4.5 billion years that the planet has existed, we have swung between cold and warm periods. Ice ages have come and gone, and have lasted for up to 100,000 years. They have been followed by shorter, warmer periods, one of which we are in at the moment: the Earth's average temperature is around 4°C hotter than it was during the last ice age some 13,000 years ago.

But recently, the changes have accelerated so much that it is now on average more than half a degree warmer than it was during the 1860s. That may not seem a very big increase at all, but as a global average change it's huge for a relatively short time-span. Locally these temperature increases have been much higher. For example, in the parts of the Arctic, it's now 5°C warmer than 100 years ago. Data from ice cores suggest that the 20th century was the warmest for 600 years - and we certainly know that the final two decades were the hottest on record.

There is one major difference between previous periods of warmth and this one. In the past, they have been due to natural events and have taken thousands of years to evolve, so species have had time to adapt - but this time most of the warming is caused by all of us. We're turning up the planet's thermostat so fast that nature can no longer cope.

What are the causes?
Every time we turn on a light switch, use a computer, watch television or cook a meal, we are creating carbon dioxide (CO₂) - which is not only a naturally-occurring gas crucial to our survival, but also the main contributor to climate change.

The electricity we use is generated by power stations, most of which burn 'fossil fuels' - so called because they have been created over millions of years by the slow underground decay of vegetation and other living matter. We also burn fossil fuels in other ways - every time we drive a car or switch on our gas central heating, for example.

The three fossil fuels we burn are coal, oil and natural gas, each of which has hydrogen and carbon in its makeup. When they are burned, these components mix with oxygen in the atmosphere. The result is carbon dioxide.
Carbon dioxide and other greenhouse gases occur naturally and form a blanket around the Earth, trapping heat that would otherwise escape into space. The heat rebounds onto the Earth's surface, and the planet's temperature rises - creating what is commonly called the 'greenhouse effect'. But we have been pumping additional CO₂ into the atmosphere for 200 years, since the industrial revolution, thus intensifying the greenhouse effect and increasing the Earth's temperature. CO₂ emissions in the atmosphere have increased by about 30 per cent over the past century. To make things worse, we have also increased the levels of other natural greenhouse gases, such as methane and nitrous oxide - and if that's not enough, we are now adding ever-increasing quantities of industrial gases which themselves contribute to the powerful greenhouse effect.

At the speed our climate is changing, the world will soon be warmer than at any time in the last 10,000 years. Climate scientists are telling us to expect an average temperature increase of between 1.4°C and 5.8°C over the next 100 years. This will also have widespread impacts on climatic conditions all over the world, causing more droughts, storms, floods and other weather extremes. Hence, we are talking about climate change, not just global warming.

Trees are great natural storehouses of carbon dioxide, some retaining it for a century or more. Over the years, billions of tonnes of CO₂ in the atmosphere are absorbed by the world's forests, and this helps balance the climate. But when forests are cut down and burned - as they frequently are when being cleared for agricultural land or for urban expansion - the carbon retained for generations is released back into the air. The damage is made worse by the fact that because the forests are not replaced, there are fewer trees to absorb CO₂ when more are needed than ever before. Deforestation accounts for about a quarter of human-induced global warming.


Current threats & problems

Global impacts
Nowhere is safe from the effects of climate change and we are seeing the first signs of change now. Glaciers are already melting in places as far apart as Switzerland and New Zealand, bringing with them avalanches, soil erosion and dramatic changes to river flows. While Mt Kenya's largest glacier has lost 92 per cent of its mass since the late 1800s, 2,000 glaciers in the eastern Himalayas have disappeared in the last century. These stark statistics speak for themselves.

Away from the mountains, the oceans and seas are warming, causing coral to die and putting many marine creatures at risk. Warmer water occupies more space than cold water, so as the oceans gradually heat up, they also expand - threatening to inundate low-lying coastal regions, many Pacific islands, and coastal wetlands as far afield as Argentina and Bangladesh, Nigeria and the United States.

Cold kills germs and disease-bearing insects such as the mosquito. But as the planet warms up, germs, bacteria and other carriers will multiply. Longer and hotter heatwaves caused by climate change are already creating perfect breeding conditions for rats and other pests, and diseases such as plague and malaria are on the increase.

But it's not just warmer weather that's causing concern. Global warming has an impact on climate patterns more broadly and is likely to cause more weather extremes, such as heavy rainfalls or prolonged drought. El Niño periods, which already turn the weather upside down in the Pacific every few years, may become more frequent and intense.

In the UK, winters will become wetter and summers will become drier. Sea levels will continue to rise, threatening the south and east coasts in particular. Skiing in Scotland is likely to become a thing of the past as the amount of snowfall decreases by up to 90 per cent. There are even some suggestions that climate change could affect the Gulf Stream, giving the British Isles a colder rather than a warmer climate. We simply can't predict with total certainty what will happen. But do we really want to risk such unexpected consequences?

Among the other victims of climate change will some of our most treasured habitats and species. Some animals will be able to adapt to a warmer world, but for many, the change will be too abrupt and they will die. Because we've destroyed so many wild spaces, some species will simply have no suitable place to which they can move.

Polar bears at risk
Global warming has caused Arctic temperatures to rise by 5°C over the past 100 years, and the amount of sea ice - essential to the survival of the polar bear - has decreased by six per cent over the past 20 years. Scientists now predict a 60 per cent loss of summer sea ice by around 2050, which would more than double the Arctic's ice-free season from 60 to 150 days. Sea ice is used by polar bears as a platform from where they hunt ringed and bearded seals, their primary prey. Retreating ice cover and longer ice-free periods limit the time the bears can spend on the ice, so they will have to use more of their vital fat resources to survive during the longer summer season. That means their body weight will fall - and lower body weight reduces female bears' ability to lactate, which in turn leads to greater mortality among cubs. Fewer than 44 per cent already survive the ice-free season.

Visit WWF's polar bear tracker on the internet at www.panda.org/polarbears. You will be able to track the movements of two tagged polar bears on Svalbard to see how they face up to the receding ice.

Scientists around the world are telling us urgently that climate change is real, it is here, and it is serious. But they also believe that it is not too late for action - so long as we act now.


What WWF is doing

What can be done by government and industry?
Most of the blame for greenhouse gas emissions lies with people in the prosperous developed world. The United States is the world's largest CO₂ emitter, accounting for around 20 per cent of emissions created by just 4 per cent of the global population. The UK is the seventh largest global emitter: each of us emit more than twice as much CO₂ than the global average. Emissions in the developing world are growing rapidly, but on a per capita basis, they have a long way to go before they catch up with us. In the meantime, it's our responsibility to reduce emissions of greenhouse gases and some progress is being made. WWF is working with key audiences in government, industry, education and society generally to address the problem of climate change.

At the United Nations climate summit in Kyoto in 1997, legally binding targets were agreed that should result in industrialised countries reducing their emissions of the six main greenhouse gases by just over five per cent by 2012, compared with 1990 levels. While this is not enough to avoid the risk of dangerous climate change, at least it's a first step towards tackling the problem. Unfortunately, the US has rejected the Kyoto agreement, but the rest of the world has decided to go ahead.

In Kyoto, the UK agreed to a 12.5 per cent cut in emissions. The British government has also set itself a separate domestic target for carbon dioxide - to emit 20 per cent less in 2010 than in 1990. In the longer term, however, we will need much tougher targets: a 60 per cent reduction by 2050 has been suggested by the Royal Commission on Environmental Pollution.

If they are to achieve their targets, governments everywhere must implement policies and measures that will lead to cleaner electricity generation (especially from renewable sources), more efficient energy use, better and more efficient public transport, responsible industrial and agricultural practices and careful forestry management. Businesses need to invest in more efficient production processes, in renewable energy and in 'climate-friendly' products. There is no simple answer, but a combination of these actions will help us all control climate change.

If we adopt these measures, there will be other benefits too. People and businesses can save money through greater energy efficiency and the negative health effects associated with air pollution from traffic and industry can be reduced.