There’s a third more carbon dioxide in the air than at the start
of the Industrial Revolution. The carbon acts like insulation in
the atmosphere, or like glass in a greenhouse — that’s why it’s
called a greenhouse gas – and it is warming the air, which warms
the seas. The current carbon dioxide concentration is higher
than it has been for several million years and rising 100 times
faster than any time in the past 650,000 years. Warmer ocean
water is already having dramatic effects. Some corals bleach and
die when water gets too warm for too long. Bleaching means
corals eject algae cells that live inside them and provide them
with food and often color. What happens to reefs will affect the
hundreds of millions of people worldwide who depend on reefs for
food and income. Ocean warming and higher air temperatures also
melt polar ice. As polar ice melts, animals that need ice
suffer. Polar bears, some seals and many penguins require ice to
live. At the base of the Antarctic food web, shrimp-like krill
require ice