Red squirrels used to be the most common squirrel in Britain. But since the grey squirrel was introduced from the USA as an illegal immigrant in the late 1800s, their numbers have nose-dived. This is partly because the greys out-compete red squirrels for food: they feed on the ground and can digest unripe acorns, which red squirrels can't. But it's not just food; grey squirrels brought a deadly virus with them, which has hit red squirrel populations hard. Sue Nelson goes to a National Trust wood near Liverpool, one of the last red squirrel strongholds in the country, to find out how they have coped with the virus. Later Richard Hollingham goes to Glasgow to find out how scientists know what Antarctica's climate was like 50 million years ago. Even though it was in the same place as it is now, temperatures on the continent were surprisingly different from what they are today.