By studying fossilized mollusks from some 3.5 million years ago, UCLA geoscientists and colleagues have been able to construct an ancient climate record that holds clues about the long-term effects of Earth’s current levels of atmospheric carbon dioxide, a key contributor to global climate change. Two novel geochemical techniques used to determine the temperature at which the mollusk shells were formed suggest that summertime Arctic temperatures during the early Pliocene epoch (3.5 million to 4 million years ago) may have been a staggering 18 to 28 degrees Fahrenheit warmer than today. These ancient fossils, harvested from deep within the Arctic Circle, may have once lived in an environment in which the polar ice cap melted completely during the summer months. The Pliocene Epoch is the period in the geologic timescale that extends from 5.3 million to 2.6 million years before the present time.