INTRODUCTION : THE OCEAN AT THE HEART OF CLIMATE CHANGE
The ocean is rarely mentioned when it comes to climate change. However, it covers more than 70% of the surface of our planet and plays an essential role in regulating the climate. This huge mass of water also acts as a tank to store greenhouse gases that humans spew into the atmosphere and which are among the main reasons for our current climate change.
However, our precious oceans are fragile. Climate change is affecting this ecosystem. Water temperatures are getting warmer, making it more acidic, and sea levels are rising! These changes have an impact on marine biodiversity, but they also affect humans. In fact, people are dependent on the ocean, as it provides a range of resources. The rising sea levels are therefore a cause for concern when we know that 10% of the global population live near the coasts within 10 meters above sea level 1!
The ocean is essential to our life on Earth, but it is now threatened by climate change.
The ocean is at the heart of the climate system. It regulates temperatures and precipitation on a regional scale and acts as the main carbon sink on Earth.
HOW DOES THE OCEAN REGULATE THE CLIMATE?
The ocean absorbs a part of the solar energy as heat. As solar radiation is at a maximum at the equator and minimum at the poles, water temperatures decrease as you move away from the equator. However, the many currents in the world’s oceans form what is called the “ocean conveyor belt”, which circulates large masses of water. On a globe scale, these currents carry warm water from the equatorial regions toward the poles and cold water from the polar regions to the equator. As some of the heat from the water is returned to the atmosphere, the ocean helps to regulate the temperature of the continents that surround it.
[Infographic 1: The major ocean currents: redistributing heat across the globe]
WHY DO WE CALL THE OCEAN A ‘CARBON SINK’?
A carbon sink is a natural or artificial tank that captures and stores carbon from the atmosphere. The oceans are the main carbon sinks on Earth, storing about 13 times more CO2 than the atmosphere, soil and continental plants combined.
This carbon storage is due to two major processes:
• biological: just like terrestrial plants, phytoplankton (all plant micro-organisms that live in water) absorbs CO2 and emits oxygen
• physicochemical: due to permanent exchanges that take place between the ocean surface and the atmosphere, some of the CO2 is absorbed and dissolved in water