Formal weather records go back 150 years. Climate scientists have an accurate picture of the earth’s varying climate stretching back millions of years. Ancient ice cores and certain geological structures contain reliable records of the earth’s past atmospheric composition and temperature. While these records indicate wildly varying climates, conditions have never changed as rapidly as they are changing now. The most notable changes due to global warming are occurring at the poles, with polar icecaps melting at an almost frightening rate.