Scientists have struggled for decades to explain a climate mystery as deep as the ocean. Oceans have absorbed almost 40% of carbon dioxide humanity has emitted from fossil fuels since 1750, considerably slowing global temperature rise, but the forces that govern how much CO₂ disappears into the deep every year are unknown. The early 1990s saw a jump in this sponge-like capacity, followed by a significant slowdown until 2001, raising concerns that the ocean may not be able to help us out forever.
Drawing on both existing knowledge and ocean data that only recently became available, new research published this week in the journal AGU Advances identifies two major influences on how much CO₂ the oceans absorb every year: the rate of industrial emissions, and the global impact of volcanoes.
The pace of fossil-fuel combustion itself helps determine how much CO₂ the ocean draws down. This finding presents a challenge to countries and companies managing pollution. As the world attempts to cut emissions to zero by 2050—which scientists say is necessary to avoid utter catastrophe—the ocean’s ability to store CO₂ will diminish with it. That complicates estimates of how quickly emissions will have to fall.
“We’re stuffing all this carbon into the ocean. Every year we’re pushing harder and harder and harder. And so the ocean in response is taking it up,” said Galen McKinley, professor of Earth and environmental sciences at Columbia University and the study’s lead author. “But when we stop pushing so hard, the ocean is going to stop taking it up.”