Climate Change

Two factors have contributed to sea level rise around the world: thermal expansion, which occurs when warm ocean waters take up more space, and the melting of ice sheets and glaciers. In the Chesapeake Bay, sea level rise is further intensified by land subsidence, or the gradual sinking of the land surface relative to sea level over time. In some parts of the watershed, rising sea levels have flooded coastal marshes and wetlands with salt water, causing wildlife habitats to disappear faster than they can move inland to higher ground.

Air and water temperatures are warming across the region, and even changes of a few degrees can stress fish, shellfish and underwater plants. Eelgrass, for example, becomes stressed when waters are warmer than 86°F for long periods of time. Striped bass and other fish experience “habitat squeeze” when surface waters grow too warm and deeper waters lack enough dissolved oxygen. And brook trout can’t tolerate temperatures above 63°F.

Average annual precipitation has increased across most of the watershed since the turn of the twentieth century, and extreme single-day rainstorms have become more frequent since 1980. High-intensity rainfall sends large amounts of polluted runoff into rivers and streams, eroding streambanks, shifting salinity levels and degrading habitat for fish and shellfish. These changes can also lead to more frequent floods.

As the amount of carbon dioxide in the atmosphere rises, so does the amount of carbon dioxide absorbed by the water. When saltwater absorbs carbon dioxide, it produces carbonic acid. This increases acidity and lowers carbonate ion levels, making it harder for oysters and other shellfish to produce the calcium carbonate needed to form their shells. A loss of oysters and their reefs would worsen water quality and wildlife habitat across the Bay.