Tree ring records capture long‐term memory in climate systems

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Measuring tree rings is a mainstay technique for estimating ancient climatic conditions, with a tree's year‐by‐year growth reflecting changes in precipitation and temperature. In some cases, paleoclimatological records compiled from tree ring measurements can stretch for thousands of years. Based on recent research, climatologists have found that hydrological and other systems have long‐term memory. Drawing on tree ring measurements compiled from across the continental United States, Bowers et al. sought to determine whether such long‐term relationships are preserved in ring width measurements. The authors analyzed the Hurst parameter—a measure of long‐term memory—of 697 different tree ring records that were collected from 10 tree species from locations across the United States. They found that though each tree species had a different mean value for its Hurst parameter, meaning that each species recorded long‐term trends in the climate differently, they all fell within the range suggestive of their being able to properly represent long‐term memory.