In old-growth redwood forests, some trees have survived for well over a thousand years. As a consequence, they provide a record of climate change. By studying tree rings, scientists have discovered that redwoods have played a significant role in removing CO₂ from the atmosphere. They have also learned that the bigger the tree, the more it grows, and hence the more carbon it sequesters. What other information can tree rings from these huge redwoods tell us about climate? By studying what has happened in the past, will we be better prepared for the future?