Julian Sachs is a chemical oceanographer who studies the mechanisms that cause climate to change on timescales ranging from decades to millennia. To do this, he and his lab develop paleoclimate records from sediment cores from throughout the world’s oceans and lakes. Molecular fossils and their hydrogen and carbon isotopic ratios are used to reconstruct past temperature, precipitation and biological productivity. Reconstructing natural climate changes in the past provides the means to determine when the modern climate is outside the range of natural variability and improves predictions of how it will change in the future. His lab also researches the effect of ocean acidification on coral reefs through in situ carbon enrichment experiments in which the impact on reef accretion and ecosystem productivity rates are measured.