Climate Change is Putting the Oceans in Peril

While some politicians claim that climate change is a hoax, and climate scientists try to refine their models and forecasts of exactly how much warming will take place in the next few decades, marine scientists can see clearly the evidence of what is already happening. 

One reason global warming has not been too bad yet is because the ocean absorbs most of the Earth’s excess heat.  But oceans are warming, due to greenhouse gas emissions.  According to the National Oceanic and Atmospheric Administration (NOAA), half of the increase in ocean heat content since 1865 has occurred over the past two decades. Warmer water holds less oxygen, but the respiration rate of animals (except for marine mammals) increases with temperature, so they need more oxygen at the same time that less is available.  A warmer ocean has less turnover (vertical water movements). These movements normally bring nutrient-rich water up from deep water to the plankton that photosynthesize near the surface.  With less nutrients, they photosynthesize less and animals can’t get enough food.

Many species are moving north to find more suitable environments, including species of commercial importance.  Lobsters are disappearing from Long Island and southern New England, but increasing in the Gulf of Maine and Canada.  Commercial catches are regulated by regional management agencies, but now these animals are fewer where they had been, and are increasing in places where they weren’t important before. 

The most dramatic responses to warming oceans are in corals.  When stressed, corals eject the single-celled symbiotic algae that live in their tissues, which normally photosynthesize and provide the coral with most of its nutrition.  When they are ejected, the coral is “bleached”- it appears white. While they can still get some nutrition by catching plankton with their tentacles, most species get less than half of their nutrition this way, so if the stress persists and zooxanthellae do not return, corals die. About 30% of the Great Barrier Reef of Australia died in 2016-2017.  This is devastating not only for the corals, but also for the thousands of other species that depend on the reef, including humans, who depend on it for $6 billion in tourism revenue annually. An excellent documentary about this tragedy, called “Chasing Coral,” is available on Netflix.

Major changes are occurring in polar regions where sea ice is diminishing rapidly. As ice melts, the water gets fresher and normal algal blooms diminish, providing less food at the bottom of the food chain on which the rest of the ecosystem depends.  Some species that depend on sea ice, like Adelie penguins in Antarctica and polar bears in the Arctic, are in trouble.

Closer to home, sea level rise (SLR) is one effect that is apparent in coastal regions. SLR results from water expanding when it warms plus addition of new water from melting glaciers. It is happening faster than was predicted. Increased flooding from storms is common, and many areas (e.g., South Florida) have flooded streets even on sunny days. Since much of the world’s population lives in coastal areas, threats to human lives and well-being are becoming apparent.  In Bristol Bay Alaska, the ability of local communities to access subsistence resources is more difficult.  Changes in the timing of ice freeze and melt are affecting safety, making it difficult to travel to neighboring villages and in some cases causing loss of life.  Residents of some small low-lying Pacific islands have already moved elsewhere, and such “climate refugees” will increase in the future, which can cause political and social problems. Despite all this, the Trump administration has recently reversed a regulation that required that development near the coast take sea level rise into consideration, to reduce the risk of future damage. 

Natural communities are also at risk.  Coastal marshes in the intertidal zone are very important ecosystems - they reduce storm surge and winds, absorb pollutants, and provide habitat for crabs, shrimp, fishes, birds, and mammals.  In the face of SLR, marshes must either increase their elevation or move inland.  Increased elevation comes from new sediments being deposited and organic matter accumulating from marsh plants. Many marshes in the Northeast are not elevating fast enough to keep up, so moving back is the only option. In developed regions, there tend to be roads, houses, etc., immediately inland, so there is no place to go. Subject to “coastal squeeze” many marshes, that protect us from storm surge and winds will disappear.  Coastal towns would be wise to buy properties next to marshes to allow for migration. 

Another component of forecasted climate change is increased rainfall in the northeast.  This will intensify flooding, and worsen the nitrogen problem in estuaries, since more rain means more runoff and nitrogen from fertilized lawns, golf courses, and farms going into the water. Warmer water in the future will also accelerate algal blooms.

Climate change is doing something else that is equally dangerous. The oceans absorb about a third of the carbon dioxide emitted from burning fossil fuels. In one way that's good, because it slows down the warming, but once in the ocean, CO2 combines with water to form carbonic acid, making the water more acidic, in fact 30% more acidic in recent decades.  This affects marine animals; the most severe is impairing shell formation in animals with calcium carbonate shells, such as clams and mussels.  This has already occurred: in the Pacific Northwest, oyster larvae in hatcheries are unable to make their shells properly.  Tiny planktonic snails are showing eroded shells.  Acidified water poses an additional stress to corals already suffering from rising temperatures.  Another effect is on behavior.  Acidified waters were found to impair the sense of smell of fish, causing them to be unable to find their home reef, and to move toward, rather than away from, the odor of a predator. These effects could result in  major problems for populations.

 

What can be done? We need rapid decreases in emissions of greenhouse gases, especially carbon dioxide. While governmental actions are vital and it is important to keep up the pressure on elected officials to do more, collectively individuals can make a difference. Examine your “carbon footprint.”  Does your car use a lot of gas?  Next time, buy a hybrid or electric, if you can afford to.  Do you drive short distances that you could walk or bike, or take public transportation? How high is your electric bill?  Could you keep your house a bit warmer in the summer and a bit cooler in the winter to save energy?  Have you put solar panels on your roof?  Solar technology has improved greatly and the price has gone down.  Could you eat less meat and more vegetables?  Animal agriculture, especially beef, creates a huge amount of greenhouse gases.  All these actions will make the quality of life better for your children and grandchildren.