Paris - By mid-century, higher levels of carbon dioxide (CO2) in ocean water could leave fish "intoxicated", becoming lost at sea, a study said on Wednesday.
The oceans absorb about a third of the CO2 released by mankind's burning of coal, oil and gas - their chemical composition changing over time to become more acidic.
Scientists from the University of New South Wales in Australia have now calculated that rising CO2 concentrations could cause a phenomenon known as hypercapnia in fish already by 2050 - much earlier than once thought possible.
"Essentially, the fish become lost at sea," lead author Ben McNeil said in a statement of the condition.
"The carbon dioxide affects their brains and they lose their sense of direction and ability to find their way home. They don't even know where their predators are."
McNeil and colleague Tristan Sasse based their projections on worst-case-scenario carbon dioxide trajectories, implying that humans do nothing to curb their emissions.
"We've shown that if atmospheric carbon dioxide pollution continues to rise, fish and other marine creatures in CO2 hotspots in the Southern, Pacific and North Atlantic oceans will experience episodes of hypercapnia by the middle of this century - much sooner than had been predicted, and with more damaging effects than thought," said McNeil.
This threatened profound impacts for commercial and subsistence fishing, the duo warned.
The world's nations sealed a climate pact in Paris last month to limit average global warming to two degrees Celsius by cutting back on emissions.