Complex sentence: The reason why it's believed that the island is a cold environment is because it turns white fairly early in the autumn on satellite photos, but this is cause of the sheep that starts to grow out their wool after the local tribesmen skin them every spring.
Split into simpler sentences: The reason why it's believed that the island is a cold environment is because it turns white fairly early in the autumn. This is cause of the sheep that starts to grow out their wool after the local tribesmen skin them every spring.