OUR actions today will change the world’s oceans for thousands of years. That is the conclusion of a study simulating a little-discussed consequence of climate change: it could choke entire ecosystems by cutting oxygen levels in the ocean. In the most extreme scenarios, with the planet warming by almost 10°C, the oceans could be starved of oxygen for 8000 years.
Oxygen-poor waters have always existed in the sea, but in the last 50 years these “oxygen minimum zones” have grown. Climate change is one cause: the sea is warming, and warmer water can dissolve less of the gas.
Marine life is sensitive to these anoxic conditions, so a fall in oxygen of just a few per cent is enough to put enormous stress on ecosystems. The Late Devonian extinction 360 million years ago, one of the biggest die-offs ever, unfolded largely in the oceans. It wiped out a fifth of all families in the tree of life, and anoxia was a key contributing factor.