Kittiwakes are beautiful seabirds. In summer, many thousands breed on cliff ledges in north Britain. You can recognise them immediately by their calls which sound just like their name. But these poor birds and other 'common' seabirds like guillemots and fulmars, are in big trouble. Their food -- sand eels -- just isn't there any more. There aren't many eels because they too are hungry. They normally eat certain types of plankton but the plankton are moving further north. Why? Because the North Sea waters are warming up and the plankton can't survive in warm water.

No plankton means no sand eels. And that means that birds which fish for sand eels can't find enough food to feed their chicks. So the chicks starve to death. This seems to be happening more and more often as each year goes by.

The warming affects everything from sand eels to seals because the nutritious plankton -- the bottom of the food chain -- just aren't there like they used to be. Other fish are also going hungry for the same reason. Salmon and cod numbers are the lowest they've ever been. This is partly because fishermen have caught too many in past years. But wamer waters and warm-loving but smaller and less nutritious plankton mean that neither fish nor seabirds breed successfully any more. So the numbers of fish like cod or seabirds like kittiwakes gets fewer each year.

(This means that Britain's favourite takeaway food, cod and chips, will also be hit.)

So what's going on? Why are the seas warming? You've probably guessed the answer. It's just one of many indicators which tell us clearly that our planet is heating up. Climate change doesn't just affect the atmosphere. It warms the oceans and the land too. And it's happening because of what people are doing: burning fossil fuels in cars, aeroplanes, industry and heating or cooling of homes and workplaces.

To find out more about global warming and why it's happening, check out my climate change guide.

If you want to find out more about the birds and fish in the North Sea, follow the links at the bottom of this page.