Air above Delaware River Basin has risen 3 degrees in a century, experts say

The average annual air temperature in the Delaware River Basin has increased by 3 degrees over roughly a century — one of multiple indicators scientists said this week paint an “overall picture of dramatic and accelerating climate change.”

The scientists gathered with governmental leaders at the biennial conference of the nonprofit Partnership for the Delaware Estuary (PDE) to share their findings that warming the last 30 years increased at four times the rate of the period from 1910 to 2021.

“Temperatures are rising quite rapidly,” Raymond Najjar, a Penn State oceanographer said in a keynote address at the conference in Atlantic City, attended by about 250 people. As he spoke, January was nearing its end at nearly 10 degrees above normal.

Najjar also spoke about the impact of climate change on Philadelphia, the largest city on the estuary, or tidal part of the Delaware River. In Philadelphia alone, sea level is rising at a rate that suggests an additional foot by the end of the century.

Najjar cited data from the U.S. Historical Climatology Network (USHCN) database that was compiled from 15 weather stations spread across the basin. The air temperature acceleration, he said, “really stood out” as the rise over the last three decades occurred as quickly as the rise over 300 years prior.

Najjar was the coauthor with Jill Arriola, an assistant research professor in Penn State’s meteorology and atmospheric science department, of the climate chapter in the partnership’s comprehensive 2022 Technical Report for the Estuary and Basin, which gets updated every five years. Andrew Ross was also a coauthor.

The report notes trends within the huge area of land and waterways in New York, Pennsylvania, New Jersey, and Delaware that drain into the 330-mile-long Delaware River. The nontidal upper river runs 200 miles from the headwaters in New York to Trenton; the tidal lower runs from Trenton, through Philadelphia and Wilmington, before emptying into the Atlantic Ocean.

Climate change, combined with development and pollution, can have a dramatic effect on the basin, the report states. It can alter water chemistry, worsen harmful algal blooms, reduce water clarity, increase salinity, and cause more flooding. The river is a source of drinking water for 13 million people.

Overall, the report rates the health of the river basin as “fair,” given positive trends such as cleaner water, restoration projects, dam removal, and increases in wildlife, such as ospreys, blue crabs, and sturgeons.

Modeling suggests some parts of the basin would be 12.6 degrees warmer at the end of the century compared with the period of 1986 to 2015 if greenhouse gas emissions continue to increase, the PDE report notes. But, even if gases decline, temperatures would still rise 7.2 degrees.

“This accelerated warming is probably the clearest and most dramatic indicator that the climate of the Delaware Estuary and Basin is changing rapidly,” the report states.

Warmer temperatures in the basin will likely make people living in some Philadelphia neighborhoods increasingly uncomfortable, Najjar said, as they grapple with an ever more sweltering heat island effect — referring to areas with high concentrations of buildings and roads that absorb and reemit the sun’s heat more than leafier areas.

“This shows how social justice issues interact very clearly with climate change,” Najjar said. “Those that are getting affected by climate change are most vulnerable.”

Sea level rise not only affects the Atlantic Coast, but up through the tidal Delaware.

In Philadelphia, sea level rose 3.1 millimeters (.12 inches) on average a year over the last 120 years. But that has accelerated to about 4.7 millimeters (.18 inches), the last 30 years — a rate suggesting an additional foot of sea level rise by the end of the century.

A low-lying section of Camden rimmed by waterways, including the river, is already struggling to contain additional flooding that officials believe is caused in part by climate change.

» READ MORE: ‘Every time it rains’: Floods from climate change plague a Camden neighborhood

Sea level has risen at the mouth of Delaware Bay by about 7 inches over the last 30 years, increasing the amount of salt in the water. By 2100, sea level rise is projected to increase by 20 inches at the low end of forecasts to up to five feet compared with the average level in 2020. The effect is compounded because the surrounding land is sinking because of its geology.

Overall, the report states, sea level rise contributes to property damage, beach and dune loss; pushes in saltwater that kills forests, and causes public safety issues during floods.

Though data suggest water temperatures might be increasing, scientists say more monitoring and analysis are needed. And, although precipitation is increasing, especially in the upper basin, the overall trend is also not clear.

However, the report expects a trend toward less snow to continue and “not only represent a shift in the character of winter in the Delaware Estuary and Basin but should also be of concern to water resource managers and local economies that rely on winter recreation.”

As the conference wrapped up Wednesday, Philly ended a 325-day snowless streak with 0.3 inches of quickly melting snow.