Image Credit: Dr. Richard Alan Keen

“The summer climate of Philadelphia, and other large cities similarly situated, is an artificial torrid zone, in which the thermometer rises from four to six degrees higher as it does at a distance of a few miles in the country.”

This was Charles Caldwell, a physician, in 1801.

Caldwell was trying to understand why Yellow Fever, a tropical disease, kept recurring in Philadelphia in the 1790s. The chief contributors to Philadelphia’s “factitious climate,” according to Caldwell: deforestation, overbuilding, fuel use, and pavement.

Sound familiar?