This is a Soay Sheep.
Its breed has been the object of countless ecological studies over the last several decades--but one recent analysis of data in particular shows something of great relevance: due to the increase in temperatures since 1985 (the year the study began), the average size within the sheep population has shrunk 5%.
Historically (since the 1930s when the sheep were introduced to the now isolated island of Soay just outside Scotland), natural selection has favored larger sheep (which conserve energy much more efficiently) due to the intense winters. However... as time has grown, the winters of this island have shortened dramatically--causing the species of grass on the island to multiply more substantially before the ground freezes, which in turn means a greater amount of food for the sheep (creating less competition throughout the group for food--the smaller sheep can now survive while previously they could not).
And now that the smaller sheep are capable of survival, they are also capable of breeding--passing on the genes to create more of their size.
Of particular interest in this study is the complexity of changes brought forth by climate change--what's bad for one population very well may be fantastic for another.
Though it certainly has its negative effects, those who have an interest in biological shifts and changes are very much taking an interest in global warming on an intellectual level--through the history of evolution, it's been shown that the massive changes in the structure of life tend to occur in times of intense change in a group's surroundings (this is why the largest amount of biological diversification occurs just after mass extinctions!).
Static conditions makes for static evolutionary alterations--who knows what sorts of unexpected evolutionary twists and turns we'll be seeing in the future?