A 100-year picture of a changing bay climate

Researchers use a century of data to chart warming Chesapeake region

Frost coated the Chesapeake Bay region about 100 times a year in the early 1900s. A century later, there are about 30 fewer chilly mornings.

The number of balmy nights, during which temperatures don’t drop below 68 degrees, has grown by a similar margin. Plants spend a month less in winter hibernation than they once did.

Climate change is not an abstract concept about microscopic changes in carbon dioxide levels or subtle rises in sea level, scientists at the University of Maryland Center for Environmental Science say. It’s already evident in the Chesapeake.

The center’s researchers have gathered more than 100 years of data from continuously monitored sites around the bay to document what has been occurring so gradually that it’s mostly unnoticed by area residents.

The scientists analyzed trends in temperature and precipitation, looking at extremes and variability, to show the ways climate has changed, often imperceptibly, over generations. They found that the changes, as subtle as they might seem, have been significant. Rainfall, for example, has increased by more than 4 inches over a century, a gain of 12 percent.

Several papers outlining the findings are being reviewed for publication in scientific journals. The articles will explain the extent to which climate already has changed around the Chesapeake and how it could threaten bay ecology in the future.

But, perhaps more importantly, the researchers say, they want to share the data with the public to illustrate what can be a confusing and controversial topic. They have launched a website designed to better inform the casual bay advocate, added a chapter to a textbook on the ecology of the Chesapeake offered for use in middle- and high-school classrooms, and they are sharing their findings with other state and federal environmental agencies to disseminate the message.

They hope that presenting climate data on a local level “would make people who live around the bay feel ownership around the data and the processes we’re describing,” said Victoria Coles, a research assistant professor at the center’s Horn Point Laboratory in Cambridge.

Coles and Raleigh Hood, a professor at Horn Point, have spent the past two years studying 114 years of data from around the bay.

The observations come from Eastern Shore, Southern Maryland and upper bay outposts of the National Estuarine Research Reserves, a division of the National Oceanic and Atmospheric Administration. Data also was collected at four such reserves along the York River in Virginia, and at 18 other stations from the Susquehanna River to the mouth of the Chesapeake.

They chose to focus on the weather trends that tend to stick in memories — periods of unusual warmth or wetness, for example — to help people compare their experiences