BOB HIRSHON (host):
Death & climate change….I’m Bob Hirshon and this is Science Update.
Agriculture has been warming the planet for thousands of years by releasing greenhouse gases like carbon dioxide into the atmosphere. But between 1500 and 1750 A.D., the planet grew colder, during a period called the "Little Ice Age". Scientists attribute this chilly anomaly to fewer sunspots and a rise in volcanic activity. But Stanford geochemists Richard Nevle and Dennis Bird have uncovered evidence that mass death was also responsible. At the time of European contact, about 60 million people were living in the Americas. But deadly new diseases decimated the population. Nevle says this allowed huge forests that had been cleared for agriculture to grow back.
RICHARD NEVLE (Bellarmine College Preparatory School/Stanford University):
Reforestation sucks carbon dioxide out of the atmosphere as trees acquire biomass.
He says this was enough to cool the planet. I’m Bob Hirshon, for AAAS, the science society.