What is climate change?
Media playback is unsupported on your device BBC News looks at what we know and don't know about the Earth's changing climate. What is climate change? The planet's climate has constantly been changing over geological time. The global average temperature today is about 15C, though geological evidence suggests it has been much higher and lower in the past. However, the current period of warming is occurring more rapidly than many past events. What is the "greenhouse effect"? The greenhouse effect refers to the way the Earth's atmosphere traps some of the energy from the Sun. The energy that radiates back down to the planet heats both the lower atmosphere and the surface. Scientists believe we are adding to the natural greenhouse effect with gases released from industry and agriculture (known as emissions), trapping more energy and increasing the temperature. Most man-made emissions of CO2 are through the burning of fossil fuels, as well as through cutting down carbon-absorbing forests.
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