The ocean covers about 71% of Earth's surface, and it plays a central role in shaping our climate. It stores heat, moves warmth around the globe and absorbs a large share of the carbon dioxide humans release.

A giant heat reservoir

Water can store far more heat than air. Scientists estimate that the ocean has absorbed more than 90% of the extra heat trapped by greenhouse gases in recent decades. Without it, air temperatures on land would have risen much faster.

Ocean currents: the planet's conveyor belt

Currents carry warm water from the tropics toward the poles and bring cold water back. This circulation helps explain why some regions have milder climates than their latitude would suggest. Changes in these currents can affect weather patterns far away.

Absorbing carbon

The ocean absorbs roughly a quarter of the carbon dioxide emitted by human activities. Tiny marine plants called phytoplankton also capture carbon through photosynthesis and produce a large share of the oxygen we breathe.

The ocean has been quietly slowing climate change for decades, but that help comes at a cost.

The cost to the ocean

• Warming waters contribute to coral bleaching and push fish species toward cooler areas.
• Acidification happens when absorbed carbon dioxide makes seawater more acidic, making it harder for shellfish and corals to build shells and skeletons.
• Sea-level rise results from warming water expanding and from melting ice on land.

Why it matters to everyone

Billions of people rely on the ocean for food and income. Coastal communities depend on healthy reefs and mangroves for protection from storms. What happens in the ocean eventually affects all of us.

What can be done

Reducing greenhouse gas emissions is the most important step. Protecting marine areas, restoring coastal ecosystems and reducing pollution and overfishing also help the ocean stay resilient.