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Oct. 14, 2011

Climate change FAQ: What’s the deal with tree rings?

by Neil Wagner

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Chris asks:
I know scientists use tree rings and ice cores to look for information about climate change. Looking at a tree stump someplace or a sliver of ice at the South Pole? So what? How is that supposed to tell us anything about the history of the world?

Answer:
Let’s start with tree rings:

  • If one scientist, working in a vaccum, only looked at one tree stump, I’d say you have a point. But there’s a lot more to the process than that. Reading tree rings is time-tested and well-understood. There’s been plenty of opportunity to match tree rings to modern, well-documented weather conditions.
  • Scientists don’t just read one tree’s rings. Some trees can live a long time —the bristlecone pine close to 5,000 years. Researchers use cross dating (overlapping and reconciling trees’ ring records going back in time) to form extended histories. The University of Missouri has a timeline going back 20,000 years.
  • This information does not exist in a vacuum. The rings are referenced, compared and contrasted with a host of other sources: ice cores, sediment layers and historical accounts to name just a few.

Now let’s look at ice cores:

  • Ice cores are as close as we can get to having a time machine. Ice cores can be miles long and contain ice from hundreds of thousands of years ago. As Bebbo and Kito found out, they’ve identified snow that fell between 1 B.C. and 1 A.D. — when Jesus Christ was born.
  • The National Ice Core Laboratory says ice cores “can include temperature, precipitation, chemistry and gas composition of the lower atmosphere, volcanic eruptions, solar variability, sea-surface productivity and a variety of other climate indicators.”
  • Ice cores are decidedly not local. First, they can contain artifacts from around the world. The Chernobyl disaster can be found in ice cores. Volcanic ash from the Toba supereruption in Indonesia 75,000 years ago? It’s in there. Second, ice cores have been extracted from around the globe — every continent except Australia, in fact.

MORE ABOUT WHAT ON EARTH?

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Interview: Katie Kline, Communications Officer at Ecological Society of America interviewed me via Skype for the ESA’s Ecotone blog. Read and hear it here.

Video: Bebbo and Kito were featured in one of Jim Parks’ terrific Today’s Green Minute episodes. See the video! Learn moreabout it.

About Neil Wagner

Neil Wagner's What on Earth? comic strip uses humor to discuss global warming.

The views expressed are those of the author and are not necessarily those of Science Friday.

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