Although marine species are more difficult to see and less well studied than land and freshwater species, they are known to be experiencing some of the same—and some different—effects from global warming.
See how the effects of global warming in the North Sea ripple up the ocean food chain—and find other hot spots where sea life is at risk on the Climate Hot Map.
- Forced migrations. Cold-water species are on the move, seeking cooler, deeper, or higher-latitude waters, while warm-water species are moving to places formerly too cold for their survival.
- Disease. Scientists are detecting marine diseases, such as lobster-shell disease, in waters historically thought to be too cold. There is some indication that higher ocean temperatures—between 86 and 95° Fahrenheit (30 to 35° Celsius)—promote optimal growth of several coral pathogens.
- Coral bleaching. As seawater temperatures rise above the range that corals can tolerate, they are expelling their symbiotic algae and exposing white skeletons—a process known as bleaching.
- Harm to wetlands. Coastal wetlands, salt marshes, and mangroves are highly vulnerable to inundation as sea levels rise, unless they can migrate inland unimpeded. More frequent droughts in upland and coastal areas may also reduce the flow of freshwater into these brackish ecosystems, contributing to marsh dieback and shoreline retreat. Freshwater from melting land ice and extreme rainfall—the results of global warming—dilutes salinity levels near shore, potentially disrupting the delicate balance among creatures in these productive waters.
In addition, retreating sea ice exerts a cascading influence on marine ecosystems. For example, it affects ocean bottom-dwelling species that depend on plankton blooms near the ice edge, on up the marine food chain to the commercially valuable fish species that lived where the ice edge used to be.
Also, oceans become more acidic as they absorb carbon dioxide. The aragonite, a crystal form of calcium carbonate, formed by tiny organisms then become too corroded to survive in high-pressure or cold waters including some parts of the shallow North Pacific, the southern ocean and the deepest waters of the ocean.