Tree-ring analysis has solved many historical mysteries
History is only as good as its sources. It is limited largely to what has survived of written records, and in prehistory to random fragments unearthed by archaeologists and paleontologists. Climate history is no different. As the effects of global warming accelerate, it becomes ever more urgent to reassemble what we can of the atmospheric conditions of the past to gather evidence from wherever it may be. Glacial ice cores are one place, with their frozen snapshots of long-ago air and traces of ash and pollen and greenhouse gases such as carbon dioxide or methane. Other climate proxies include the annual accretion of stalagmites, the growth of corals and the
