(Describer) An ocean wave rolls in.

(female narrator) Scientists refer to ocean acidification as "the other carbon problem." The first, of course, is global warming. People have heard about global warming for decades.

(Describer) Lisa Suatoni:

But for the past five years experts have really understood that the carbon dioxide is affecting the oceans as well.

(Describer) Ken Caldeira:

(man) When we burn coal, oil, and gas, we introduce carbon dioxide into the atmosphere. But the atmosphere touches the ocean over 70% of Earth's surface.

[thunder rumbles]

This carbon dioxide we're putting into the atmosphere, we are also putting into the ocean.

(narrator) What happens when so much carbon dioxide-- 22 million tons of it each day-- mixes with ocean water? In terms of chemistry, the answer is simple. It becomes an acid.

(Describer) Suatoni:

(Suatoni) Since the Industrial Revolution, the ocean acidity has increased by 30%. If we continue to pollute as we are now, ocean acidity will double by century's end compared to pre-industrial times. That is a big problem.

(narrator) Thousands of ocean species build protective shells to survive. These organisms create their shells by drawing certain molecules from the water around them. But rising acidity depletes those molecules. And when acidity gets too high, shells dissolve. Shell in polar water conditions predicted for 2100.

(Describer) A snail shell dissolves in polar water conditions predicted for 2100. Ove Hoegh-Guldberg:

(man) Coral reefs are sensitive to ocean acidification because corals can't form skeletons as quickly as before, and reefs are starting to disappear. 2003 reef collapse We may lose those ecosystems within 20 or 30 years. In those structures live an estimated million species.

(Describer) By a reef, different fish dart away.

(narrator) There's growing alarm that higher acidity will extinguish creatures that are a basic food source for fish.

(Describer) A large fish eats a crab. Another grabs another shellfish, and another takes a striped fish.

In many parts of the world, fish are a basic food source for people.

(Describer) A beach is filled with boats and nets.

The only way to stop acidification is to emit less carbon dioxide.

(Describer) Many seals swim underwater.

But the ocean can better defend itself against rising acidity and temperature if its systems are healthy.

(Suatoni) That means restoring depleted fish populations, establishing global marine protected areas, and reducing nutrient pollution in coastal zones.

(man) Today we're in a remarkable history of the ocean.

(Describer) Steve Palumbi:

We know how to solve the local problems of marine ecosystem health and the global problems. The question is, will we?

(Describer) Video content provided by: Natural Resources Defense Council. Accessibility provided by the US Department of Education.

Accessibility provided by the U.S. Department of Education.