What is the climate?
The climate is the average weather over a long period of time. The climate depends on how much radiation (heat) reaches the earth from the sun, and how much radiation is given off by the earth. Normally this is roughly equal, and allows life on earth to exist. Anything that upsets this balance will cause temperatures to change.
Over the past two million years there have been times of very cold weather (glacial periods or ice ages) and warmer weather. The last ice age was 20,000 years ago. Because most of the oceans were frozen, the sea was lower and temperatures were colder than today. As the weather gradually became warmer, the glaciers and ice melted and the sea rose. Plants grew on the land. These changes were due to natural causes. However, some recent changes in temperature have been caused by people.
Greenhouse gases and global warming
Greenhouse gases are released during manufacturing, farming and other activities carried out by people. The gases form a layer that traps the radiation given off by earth and keeps it in the atmosphere like warm air in a greenhouse. This causes the planet to warm up. If it gets warmer, more ice will melt into the oceans and low-lying countries will be flooded by the rising sea level. This is one of the biggest issues to do with the future climate.
The Kyoto Protocol
The Kyoto Protocol is an international agreement to control global warming and reduce climate change. New Zealand and many other countries have signed the agreement. It aims by 2012 to reduce greenhouse gases to below the levels they were in 1990.
Predicting the future climate
Scientists work out the future climate using powerful computer programs. These take into account what happens in the atmosphere, in the ocean and on land, and the level of greenhouse gases.