What an­cient storms blew into the arc­tic

Popular Science - - TALES FROM THE FIELD - ERICH OSTERBERG, CLI­MATE SCI­EN­TIST AT DART­MOUTH COL­LEGE

At the poles, snow doesn’t melt; it ac­cu­mu­lates in lay­ers of ice that stretch back in time like tree rings. I study par­ti­cles trapped in these lay­ers to see how cli­mate has changed.

First, my team gath­ers ice cores from the cold­est climes. In Green­land, we tra­verse thou­sands of miles on snow­mo­biles to reach dif­fer­ent col­lec­tion sites, sur­rounded by noth­ing but flat, white beauty. Then we drill for sam­ples that range from a cou­ple hun­dred feet to more than a mile long and date back up to 50,000 years.

Green­land cores pre­serve specks of dust from Chi­nese deserts and sea salt from big storms in the North At­lantic. But there are so few par­ti­cles—some are one in a tril­lion—that it’s like try­ing to find a postage stamp some­where in New York City. We melt a cross-sec­tion of ice and use a spe­cial in­stru­ment to count in­di­vid­ual flecks.

These tell us what the cli­mate used to be like. For ex­am­ple, winds had to be strong to carry larger dust motes thou­sands of miles. Lit­tle dif­fer­ences in the weights of oxy­gen and hy­dro­gen in wa­ter mol­e­cules tell us about the tem­per­a­ture when they fell as snow thou­sands of years ago—and how that com­pares to ris­ing tem­per­a­tures to­day.

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