Answer:
C. Sea ice.
Explanation:
Climate change is popularly denoted as the heating up of the planet due to the release of larger amounts of CO₂ into the air. CO₂ absorbs less heat, keeping it in the atmosphere longer, which leads to a general warming up in a very long period of time.
Sea Ice, in this case, can only exist in cold environments, and if the world is generally heating up, then the temperatures in which sea ice can exist would slowly fade, resulting in the melting of sea ice, and the adding of large volumes of water into the oceans.
However, it is worth noting that the earth does experience cycles of general warming and cooling throughout it's centuries, and so the current period of global warming may not be as bad as people may say it is.
