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Rapid Sea Surface Changes Pose Risks

Researchers find new ocean conditions may emerge as others disappear, challenging species

Photo of reddish sunset over ocean with sailboat
Courtesy of Pixabay.com

Rapid changes in Earth’s climate could spell changes for the ocean and set up dire conditions for marine species, according to research by NOAA and partners. Depending on the rate of change, the conditions could pose challenges that may be without precedent for many species.

An anticipated rise in global temperature of 1°C to 3°C (1.8°F to 5.4°F) and increases in ocean acidification over the remainder of the 21st century underlie this unprecedented ecological stress, according to the authors of the paper “Novel and disappearing climates in global surface ocean,” published in Nature Scientific Reports

“Despite evidence that some marine species may be able to keep pace with climate change through distribution shifts because of high dispersal potential, range shifts no longer become a viable strategy if globally the climate shifts beyond what they can tolerate,” the researchers stated. “Thus, novel climates with no analog in recent evolutionary history may leave species in an ‘adapt or die’ scenario.”

Novel and Disappearing Ocean Climates

Unlike previous research, the new work examined novel and disappearing climates across the entire ocean surface. The work looks at ocean climatologies, which are defined by long-term averages of a given variable, like sea surface temperature, over various time periods, usually spanning multiple decades. For this study, the analysis considers multiple variables simultaneously, instead of a single variable at a time. A novel ocean climate is one in which the temperature and chemistry of the water is different from that previously observed in the ocean surface, while a disappearing climate is one in which the temperature and chemistry of the water is common today, but will be rare or absent in the future.

The researchers calculated the “degree of global novelty” in sea surface conditions to the “degree of global disappearance.” They determined the degree of global novelty or disappearance based on several characteristics found in the present-day sea surface: seasonal temperature, pH, and the saturation state of aragonite—a calcium carbonate mineral and important building block for corals, bivalves, and many marine organisms.

Graphic showing areas of the ocean where changes could occur due to climate change, posing risks to marine life.

Courtesy of NOAA NCEI, Deb Misch

Disappearing Climates 

A substantial proportion of the sea surface is projected to experience a moderate-to-extreme degree of global disappearance between the years 2000 and 2100, depending on the extent of climate change. By 2100, between a range of 35.6% and 95% of the sea surface is predicted to experience an extreme degree of global disappearance. The wide range reflects the uncertainty of future global emissions of CO2 and when those may peak. Locations with climates that are projected to experience the most extreme degree of global disappearance are widespread in the Tropics and the temperate regions of both hemispheres.

Novel Climates

A substantial proportion of the sea surface is also projected to experience a moderate-to-extreme degree of global novelty between 2000 and 2100, depending on emissions. By 2100, between 10.3% and 81.9% of the sea surface is predicted to experience an extreme degree of global novelty. Locations with climates that are projected to experience the most extreme degree of global novelty are primarily located near the equator, in the Arctic, and in the subpolar region of the Southern Hemisphere and become more widespread under the highest scenario of CO2 emissions.

Challenge to Species

When calculations were applied to ocean conditions between the years 1800 and 2000, the researchers could not pinpoint any instances of extreme novelty or extreme disappearing ocean climates. So, in terms of how species may adapt, the pre-21st century data didn’t provide those clues. The adaptive capacity of species at a particular location remains unclear. 

“If a majority of the ocean surface climate disappears and is replaced by novel climates with no recent analog by the end of the 21st century, the optimal environment for many species may not exist and dispersal will not help these species keep pace with environmental change,” the researchers state

The degree of global novelty or disappearance for a specific location is relative to the amount of variability historically experienced at an ocean location, according to the authors. An area that has historically experienced high variability may also have species that have greater adaptive capacity. Other important aspects of seawater—such as chemistry, food availability, and ocean dynamics—may be altered by climate change but were not considered by the study’s model. Additionally, coastal regions were excluded from the study, which are known for significant fluctuations in temperature and carbonate chemistry.

The team conducting the research included scientists from Northeastern University Science Center in Massachusetts, the Department of Natural Resources at Cornell University, and the Cooperative Institute for Satellite Earth System Studies (CISESS) of the University of Maryland, a NOAA Cooperative Institute administered by the Earth System Science Interdisciplinary Center (ESSIC). 

Reference: Lotterhos, Katie, Á. J. Láruson, and L-Q. Jiang, Novel and disappearing climates in the global surface ocean from 1800 to 2100. Sci Rep 11, 15535 (2021). https://doi.org/10.1038/s41598-021-94872-4.

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