In the late 1700s, during the early days of the United States, many scholars were debating whether human activities were modifying the earth?s climate. Thomas Jefferson wrote in 1785, ?A change in our climate is taking place very sensibly. Both heats and colds are becoming much more moderate within the memory even of the middle-aged.?
A colleague of Jefferson, Samuel Williams, a Harvard professor, suggested a human cause: ?When the settlers move into a new township, their first business is to cut down the trees, clear up the lands and sow them with grain. The surface of the earth becomes more warm and dry. As the settlements increase, their effects become more general and extensive: The cold decreases, the earth and air become more warm.?
Not everyone agreed, Noah Webster, yes, the man who created the first American dictionary, said, ?I see no reason to conclude with Dr. Williams and Thomas Jefferson that the heat of the earth is increasing. It appears that all of the alterations in a country, in consequence of clearing and cultivation, result only in making a different distribution of heart and cold, moisture and dry weather, among the several seasons.?