The world’s oceans will likely lose about one-sixth of their fish and other marine life by the end of the century if climate change continues on its current path, a new international study says.
A group of 35 researchers from 12 countries and 4 continents presented a comprehensive global-ocean assessment of climate change by using a combination of multiple climate and ecosystem models. This model ‘ensemble’ reveals that global marine animal biomass – the total weight of marine animals such as fish, invertebrates and marine mammals in the ocean – will decline under all emission scenarios, driven largely by increasing temperature and decreasing primary production.
For 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 the comprehensive computer-based study. And that does not include effects of fishing.
“We will see a large decrease in the biomass of the oceans,” if the world doesn’t slow climate change, said study co-author William Cheung, a marine ecologist at the University of British Columbia. “There are already changes that have been observed.”
For 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%.
The analysis also suggested that climate-change impacts may be more severe at higher food-web levels, meaning that fish and marine mammals may suffer more severe declines compared to phytoplankton. “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.
Projected changes of marine animal biomass by the end of the 21st century (% increase or % decrease compared to the end of the 20th century) under two IPCC emission scenarios: RCP2.6 assumes strong mitigation, RCP8.5 assumes business-as-usual emissions. ©2019 by National Academy of Sciences
“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.
Tropical areas, already warm, will also see the biggest losses, Cheung said.
Scientists had already thought that climate change will likely reduce future ocean life, but past computer simulations looked at only part of the picture or used only one model. This study uses six different state-of-the-art computer models that give the best big picture look yet, Cheung said.
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, Cheung added.
The study, “Global ensemble projections reveal trophic amplification of ocean biomass declines with climate change” was published today in the Proceedings of the National Academy of Sciences (PNAS)
Tags: climate change, William Cheung