Paleoclimatologist Darrell Kaufman (IMAGE) Northern Arizona University Caption Northern Arizona University Regents’ Professor Darrell Kaufman examines a lake sediment core he and his students recently collected from central Alaska. Credit Northern Arizona University Usage Restrictions none License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.