Last year's Earth Hour took the world by storm. People joined in from over 83 countries, in over 3000 towns and cities and switched off over 1000 famous landmarks. This year, our fave conservation boffins, WWF hope a billion people will join in and show that we care about what's happening to our planet.

WWF's Earth Hour reminds us all that our climate is changing dramatically. This is already affecting lots of animals and plants across the world. In the Arctic, the summer sea ice is disappearing which means that polar bears are losing their hunting grounds. If they can't hunt, they starve. Some science boffins predict that if nothing is done to stop climate change all the summer sea ice could have vanished by 2013. That means that polar bears could vanish, too.

That's why we need to do something! Ask your parents/guardians to sign up, here.

Get your school involved. WWF have created loads of great Earth Hour projects that your whole class can take part in. Tell your teachers about it and ask them to sign up, here, for some great teaching stuff.

And, why not organise an activity around Earth Hour? Ready, steady, go for it!

WHAT IS CAUSING CLIMATE CHANGE?

The temperature of the Earth is increasing because of waste gases produced by people's activities. (No, we're not talking about Wez's bottie burps!) We're talking about activities like driving cars, using our computers and watching TV. This increase in temperature is called global warming. The most widespread waste gas is carbon dioxide. We produce this in large amounts when we burn fossil fuels such as coal, gas and oil. We burn these to produce energy. The trouble is, we're all using more and more energy to run cars, play computer games, use washing machines etc. So, we're producing more and more carbon dioxide. This activity is heating our planet. As the Earth becomes warmer, our climate is changing.

BUT, HEY, WE ALL LIKE NICE WEATHER, DON'T WE?

Yes, we do. But climate change doesn't mean nice weather. It means more unpredictable weather. Some areas of the world are getting so little rainfall that they can't grow enough food to eat. Other areas are flooding, bringing danger and hardship to millions of people.

Play this game to learn more about the CO2 effect.

HOW CAN ONE WEBBLI MAKE A DIFFERENCE?

By supporting Earth Hour! By switching off our lights for just one hour, we show the world that we care about climate change and that the grown-ups in power should do something about it. So, tell your friends, family and school to join in and help save our wonderful planet.

Famous buildings and landmarks all over the world (like the Eiffel Tower, above) are switching off their lights to show their support. Find out which ones, here.

Schools all over Britain are joining in, too. Find out which ones, here.

But, remember, sorting climate change is not about just one hour. If everyone across the world did a few small things every day, we could save polar bears from extinction! How amazing would that be?!

LET'S MAKE SOME WEBBLIPROMISES!

Let's make a WebbliPromise to switch off our computers when we've finished using them.
Let's make a WebbliPromise to turn off the light when we leave a room.
Let's make a WebbliPromise not to leave our mobile phone chargers switched on when we're not using them.
Let's make a WebbliPromise to remind our friends and families to do the same!

Save the planet in this fun game.

WEZ SEZ: SUPPORT WWF'S EARTH HOUR!