Assigned amount units

Okay, imagine you have some stickers. Your mom gives you 10 stickers and says that's all you have for the week. These 10 stickers are like assigned amount units or AAUs.

Now imagine that you have a friend who doesn't like stickers but loves toys. Your friend has 10 toys, but his mom tells him he can only play with 5 toys a week. These 5 toys are also like assigned amount units or AAUs.

In the same way, countries who signed the Kyoto Protocol agreed to limit the amount of greenhouse gases they produce, and they were given assigned amount units or AAUs. Each country had a limited number of AAUs they were allowed to use, just like the limited number of stickers or toys you and your friend were given.

If a country produces more greenhouse gases than their AAUs allow, they have to buy AAUs from another country that has surplus AAUs. Think of it like trading stickers or toys: if you run out of stickers, you can trade with your friend for one of his toys.

This system helps reduce the overall amount of greenhouse gases by making it more expensive for countries to pollute.