Natalie Mahowald, the Irving Porter Church Professor of Engineering and a Cornell professor in the Department of Earth and Atmospheric Science.

If humanity does not act to reduce global greenhouse gas emissions, atmospheric carbon dioxide levels will continue to climb and Earth’s average temperature will escalate. This sustained climate warming will drive the ocean’s fishery yields into steep decline 200 years from now and that trend could last at least a millennium, according to University of California, Irvine, and Cornell University researchers in Science, March 9.

Scientists have examined climate change scenarios to the year 2100. Now, researchers who study the Earth’s climate system have extended the state-of-the-art Earth system models for physical and biogeochemical oceanic processes, projecting conditions through 2300.

“Really nasty things happen when you think further out in time. It’s bad enough in 2100, but when you think about 2300, it is even worse,” said paper co-author Natalie Mahowald, the Irving Porter Church Professor of Engineering and a Cornell professor in the Department of Earth and Atmospheric Sciences.

“If we don’t stop burning fossil fuel and cutting down our tropical forests – all those human activities that maintain our society – we’re going to reach incredibly high levels of carbon dioxide in our atmosphere. Keep burning fossil fuels and that will affect our oceans,” she said.

In the paper, the new model projections calculate that atmospheric carbon dioxide could reach 1,960 parts per million by the year 2250. In February 2018, the average atmospheric carbon dioxide level was 408 parts per million at Mauna Loa, Hawaii, site of National Oceanic and Atmospheric Administration global greenhouse gas monitoring.

Governments agreed in the 2015 Paris Agreement, as part of the United Nation’s effort to combat climate change, to keep the Earth’s average temperature from rising more than 2 degrees Celsius. This paper predicts that with no climate change action, Earth’s surface temperature will rise by 9 degrees Celsius – about four times beyond the Paris goal.

With higher levels of carbon dioxide and higher average temperatures, the oceans’ surface waters warm and sea ice disappears, and the marine world will see increased stratification, intense nutrient trapping in the deep Southern Ocean (also known as the Antarctic Ocean) and nutrition starvation in the other oceans.

In 200 years, Earth could see a 20 percent global decline in fishery yields, with a 60 percent decline in the North Atlantic. The decline could last at least 1,000 years or more, according to the paper.

Mahowald said current U.S. energy policies will likely lead to large negative impacts on ocean fishery productivity, but there is hope: “Renewable energy has become more affordable, so as a country, we’re moving more toward renewables,” she said.

“If we can transition to solar and wind energy quickly enough – and if it is economically viable – then we can hopefully avoid this dismal future. I hope we never reach the catastrophic levels of emissions that we use in our business-as-usual scenario,” said Mahowald, a fellow and the faculty director for Cornell’s Atkinson Center for a Sustainable Future. “Sadly, though, we could hit that mark.”

The paper, “Sustained Climate Warming Drives Declining Marine Biological Productivity,” was led by first author J. Keith Moore, University of California, Irvine. Funding for Mahowald’s research on climate dynamics and humanity’s impact on the environment was provided by the National Science Foundation and the Department of Energy.