What is global dimming?

When you put particles into the air, such as from cars, industry and volcanoes, the particles reflect some of the sun's rays back into space and stop it coming through into the atmosphere. The sun is the key source of warming and energy input into our planet. So actually in real terms when you have a big volcano, despite the fact that it releases an enormous amount of heat, it releases an enormous amount of ash. That correspondingly cools the planet. Most people might think that volcanoes would heat the planet up, but they actually cool it down for quite a long time. A recent piece of research in the journal Nature showed that Krakatoa, which blew up over Indonesia about 100 years ago, still has a legacy living on in the oceans today. Over 100 years later we can still see a cold body of water and lower sea level because of that.