When fossil fuels are burned, for example by industry, in power stations and in vehicles and aeroplanes, gases are released which enter the atmosphere. Although these gases have always been present in the Earth's atmosphere, their concentration is gradually increasing as more and more fossil fuels are burned.
Scientists believe that the build-up of these so-called greenhouse gases in the atmosphere, acts like a blanket around the planet, trapping heat inside the Earth's atmosphere. This is the greenhouse effect and the resulting increase in global temperature is called global warming.
It's thought that the build-up of greenhouse gases impacts on global temperature in two ways.
The gases allow more of the Sun's rays to enter the atmosphere. Some solar radiation is still reflected back into space by the outer parts of the atmosphere, but it is believed that the amount reflected back is gradually reducing.
At the same time, the greenhouse gases absorb more of the solar radiation that is reflected back from the Earth's surface, trapping heat and keeping it in the atmosphere. Of course the ability of the atmosphere to capture the Sun's warmth is essential for life on Earth. But if significantly MORE warmth is being captured, this is bad news for the planet.