MINNEAPOLIS — By sailing to the New World, Christopher Columbus and the other explorers who followed may have set off a chain of events that cooled Europe’s climate for centuries.

The European conquest of the Americas decimated the people living there, leaving large areas of cleared land untended. Trees that filled in this territory pulled billions of tons of carbon dioxide from the atmosphere, diminishing the heat-trapping capacity of the atmosphere and cooling climate, says Richard Nevle, a geochemist at Stanford University.

“We have a massive reforestation event that’s sequestering carbon … coincident with the European arrival,” says Nevle, who described the consequences of this change October 11 at the Geological Society of America annual meeting....