The Arctic is vulnerable because it has one of the most severe environments on the planet. Temperatures are extremely low, sunlight and precipitation are limited, and the growing season is short, averaging only 50 to 100 days. Sea ice, snow cover, tundra and permafrost are highly sensitive to subtle changes in sunlight, temperature and precipitation. Ecosystems within the Arctic exist in a delicate balance with the climate. So are more sensitive to temperature changes than temperate or tropical ecosystems. A slight shift in temperature, bringing averages above the freezing point, will completely alter the character of the region.