Earth's oceans could lose one-sixth of marine life by 2100 due to climate change

Washington — The world's oceans will likely lose about one-sixth of its fish and other marine life by the end of the century if climate change continues on its current path, a new study says. The study comes on the heels of a report published by Australian climate experts that warned human civilization faces "an existential risk" from climate change by 2050.

Every degree Celsius (1.8 degrees Fahrenheit) that the world's oceans warm, the total mass of sea animals is projected to drop by 5%, according to a comprehensive computer-based study by an international team of marine biologists. And that does not take into account the effects of fishing.

If the world's greenhouse gas emissions stay at the present rate, that means a 17% loss of biomass — the total weight of all marine animal life — by the year 2100. But if the world reduces carbon pollution, losses can be limited to only about 5%, the study said.

Last week, a new report by Australian climate experts warned that "climate change now represents a near- to mid-term existential threat" to human civilization. In this grim forecast — which was endorsed by the former chief of the Australian Defense Force — human civilization could end by 2050 due to the destabilizing societal and environmental factors caused by a rapidly warming planet.

"We will see a large decrease in the biomass of the oceans," if the world doesn't slow climate change, said study co-author and University of British Columbia marine ecologist William Cheung. "There are already changes that have been observed." Cheung added that already warm tropical areas will also see the biggest losses. 

While warmer water is the biggest factor, climate change also produces oceans that are more acidic and have less oxygen, which also harms sea life, Cheung said. Much of the world relies on oceans for food or livelihood, scientists say.

The biggest animals in the oceans are going to be hit hardest, said study co-author Derek Tittensor, a marine ecologist at the United Nations World Conservation Monitoring Center in England.

"The good news here is that the main building blocks of marine life, plankton and bacteria may decline less heavily, the bad news is that those marine animals that we use directly, and care about most deeply, are predicted to suffer the most as climate change is working its way up the food chain," co-author Boris Worm, a marine biologist at Dalhousie University in Canada, said in an email.

It is hard to separate past climate change impacts from those of fishing, but past studies have shown places where observed fish loss can be attributed to human-caused climate change, Chung added.

Tittensor pointed to lobsters off the coast of main Maine and North Atlantic right whales as examples of creatures already being hurt by global warming. University of Georgia marine biologist Samantha Joye, who wasn't part of the research, praised the study as meticulous and said it is also "an urgent call for action."

"Healthy oceans are required for planetary stability," Joye said in an email. "Aggressive global action to slow climate change is a moral imperative."