Climate Change

Like countless other parts of the world, the Chesapeake region has begun to feel the effects of a changing climate. As warmer temperatures and higher sea levels are noted in the region, Bay scientists are working to understand the possible effects of these changes on the Bay and its watershed, including how they may affect Bay restoration efforts already in progress.

What effects may climate change have on the Bay?

Some of the effects of climate change, such as sea level rise and increased temperatures, have already been recorded in both the Chesapeake region and throughout the world. Other possible impacts of climate change on the Bay include lower dissolved oxygen levels, more precipitation, and changes in wildlife abundance and migration patterns. Many species will deal with the interaction of several climate change effects, which could impact their ability to survive in the Bay region.

Sea Level Rise

Over the past century, water levels in the Bay rose about one foot due to both global sea level rise and land subsidence (slow, natural sinking of the land around the Bay). Based on global sea level rise projections for the 21st century, water levels in the Bay are likely to increase at least twice as much this century as during the last century. Sea level increases in the Bay will be greater than those worldwide because of continued land subsidence.

As water levels rise higher, the Bay will continue to lose tidal marshes faster than they are able to migrate upland. Tidal marshes filter pollution, protect shorelines and provide vital habitat for waterfowl, blue crabs and many species of fish.

Increases in Temperature

Temperatures in the Chesapeake region have warmed by nearly 2 degrees Fahrenheit since 1960. Computer models suggest that air temperatures in the region will increase another 5 to 9 degrees by the end of the 21st century. Warmer air temperatures over the past few decades have correlated with warmer Bay water temperatures.

Fewer Underwater Bay Grasses

The Chesapeake is near the southern edge of the Atlantic growing range of eelgrass, the dominant underwater bay grass species in higher-salinity parts of the Bay. Continued warm temperatures could severely reduce the amount of eelgrass able to grow in the Bay. Eelgrass becomes stressed when water temperatures reach 86 degrees Fahrenheit or higher for prolonged periods. In 2005, for example, a late-summer stretch of high temperatures killed vast areas of eelgrass in the lower Bay.

A large loss of eelgrass would affect a number of species, including:

• Post-larval and molting adult blue crabs, which hide from predators in eelgrass beds.
• Waterfowl and other aquatic animals that feed on eelgrass during the winter. Unlike other underwater bay grasses that sprout each spring, eelgrass is perennial and grows through the year.

More Precipitation

Precipitation, particularly in winter and spring, could increase as the climate changes. Wetter conditions often cause more nutrients and sediment to flow into the Bay, which could further diminish water quality and fuel the growth of more algae blooms.

Larger “Dead Zones”

Summer dissolved oxygen conditions could worsen, since warmer water temperatures are able to hold less oxygen. Higher spring river flows due to increased precipitation could also impact dissolved oxygen levels. More fresh water flowing into the Bay could lead to stronger stratification between bottom and surface waters, not allowing deeper waters to mix with oxygen-rich surface waters.

Less oxygen could affect the abundance of fish and shellfish like striped bass, sturgeon, menhaden, blue crabs and oysters, all of which require certain oxygen levels to survive.

Fewer Wintering Waterfowl

Waterfowl that winter in the Chesapeake region could decline sharply because:

• The Prairie Pothole Region of the upper Great Plains, where most ducks that winter on the Bay breed, is expected to become much drier and produce fewer ducks.
• As winter temperatures warm, migrating waterfowl may begin to spend their winters in ice-free areas farther north and west of the Chesapeake, rather than completing their migration route.
• Marshes, underwater grass beds and other shallow water habitats that waterfowl use in the winter may decline.

Influx of New Species

Some plant and animal species that are on the southern edge of their distribution range, including winter flounder, soft-shelled clams, maples, beeches and birches, could be pushed out of the Chesapeake region by a warming climate. However, the Chesapeake could become home to southern species, such as brown shrimp, groupers, spotted seatrout, hickories and southern pines.

What is the Bay Program doing to prepare for the possible effects of climate change?

The Bay Program will soon begin working with the U.S. EPA and other federal agencies to incorporate a range of potential future climate patterns into its computer models. By looking at these models, Bay scientists will be able to identify the most likely effects of climate change on the Bay, its residents and restoration efforts.