What is El Niño?

Diana - El Niño is usually defined as having occurred when you get a high air surface pressure on top of the Pacific Ocean and the actual surface of the Pacific Ocean increases in temperature. What happens as a result of this is you get the Humboldt current - that's the sort of nutrient-rich cold current of water - moving, and it moves away from the coast of South America.

That takes away all the nice happy fish, and it means that all the fishermen in South America lose a lot of their stock. And it also causes quite heavy rain and flooding in the southern parts of America. Conversely, you get droughts and sometimes even bush fires on the eastern side of the Pacific or where Australia is. This kind of thing can happen roughly every five years on average.

But as for the jet stream, we don't really know for sure, but it looks like El Niño can pull the polar jet stream slightly further south, which means that north America can suffer maybe more rainfall, maybe a bit more snow, colder winters, but we don't really know if it actually affects Europe, possibly.

Dave - Also, essentially you're changing the temperature of a great big area, a huge area, of the Pacific Ocean which will affect which area you're heating the air above, so it'll change the kind of global circulation of air currents slightly, which will have all these knock-on effects.

Diana - Exactly. It's a huge system and a hugely complex system as well and some people have even recorded maybe more droughts occurring in Africa during El Niño event, which is the other side of the world.