The number of low-oxygen areas in the world’s oceans where little life can survive is set to greatly multiply with global warming, according to a study by two Danish researchers. In a study published online by the journal Nature Geoscience, scientists built a computer model to simulate climate change over the next 100,000 years. In the worst case scenario, CO2 concentrations would rise to 1,168 parts per million (ppm) by 2100, or about triple today’s level, and the ocean dead zones would increase by a factor of 10 or more. In the best case scenario, the CO2 would reach 549 ppm by 2100, or roughly 50 percent more than today. Dead zones – where complex organisms like fish, crustaceans and mammals cannot survive because of the lack of oxygen – would increase, but the damage would not be as great.
However, even if global warming is reversed by 2100, its effects will continue for hundreds of years, says Jens Olaf Pepke Pedersen, a physicist at the Technical University of Denmark, one of the scientists on the study. Once the ocean has warmed up, it then needs hundreds of years to cool down again, Pedersen says. According to the model, “these low-oxygen areas would continue to expand and they would peak around 2,000 years from now. The ocean would then slowly recover as it cools.”
Marine oxygen depletion is believed to have played a role in the major mass extinctions in the past, such as The Great Dying, that occurred at the end of the Permian, 250 million years ago, which wiped out 95 per cent of all marine life. Areas of low oxygen exist in today in shallow areas next to the coast, where runoff from agricultural fertilizer causes a multiplication of oxygen-gobbling algae producing the dead zones.