What is climate change?

The Earth's climate has always varied, so the term climate change is now generally used to describe the changes caused by human activity - specifically, greenhouse emissions such as carbon dioxide and methane, which build up in the atmosphere and trap heat.

Is it the same as global warming?

As human activity increases the concentration of these gases in the atmosphere far beyond their natural levels, much more heat is trapped. Hence, the term climate change is often used interchangeably with global warming.

Can it be explained by natural causes?

Measurements at the Earth's surface show that average temperatures have risen by some 0.4C since the 1970s.

Scientists blamed the change on human emissions because the increase is too big to be explained by natural causes.

What is the main greenhouse gas?

Water vapour in the atmosphere produces the strongest greenhouse effect, but it has been in balance for millions of years. Human emissions, though relatively small, tip that balance.

Carbon dioxide is the chief greenhouse gas produced by human activity. It is produced when we burn fossil fuels: oil, gas and coal. The level of carbon dioxide in the atmosphere is measured in parts per million (ppm).

What temperature rise is expected in future?

Scientists say continued emissions will cause the planet to heat up further. To work out how much, they use computer models based on the programs used to predict the weather. These models are not perfect, and struggle to simulate some features of the climate system such as clouds. The computer models predict that if emissions continue to rise at the present rate, average temperatures are most likely to increase by 4C by 2100.

How can we tackle global warming?

Scientists say the only realistic way at present is to reduce greenhouse gas emissions. How to do that - and where - is a political hot potato.

Because it takes time for the heat to build up in the atmosphere, and because carbon dioxide stays in the atmosphere for a long time, there is a lag in the system, which means the effect of any changes will not be felt for decades. Put bluntly, we are headed for about another 0.5C of warming whatever we do.

Can renewable energy help?

The United Nations Intergovernmental Panel on Climate Change (IPCC) recently said that we already have most of the technology we need to bring down emissions significantly. These include renewable energy sources such as windmills and solar panels, as well as more efficient cars and power stations.

The Guardian

(China Daily 08/10/2007 page12)