PITTSBURGH (AP) — The grove of hemlock trees around where United Flight 93 crashed on Sept. 11 is being attacked by an insect that wasn't there 20 years ago. And some scientists say it's an example of how climate change combines with other factors to damage the environment.
The problem at the Flight 93 National Memorial in southwestern Pennsylvania doesn't involve melting polar icecaps, but rather hemlocks battling the deadly spread of the tiny hemlock wooly adelgid. It has only one natural predator in eastern forests — extremely cold winters.
Michael Mann, a climate scientist at Penn State University, says that while many factors influence the spread of invasive pests like the adelgid, warmer winters play a role. And Mann says scientists know that climate change is contributing to warmer winters.