Melting Arctic Ice

Melting Arctic Ice — page 1

Melting Arctic Ice — page 2 — Chapter ONE HOW DO WE KNOW IT’S MELTING On July 10 1959 geologist Paul T Walker and his colleague Albert Crary were exploring a glacier on Ward Hunt Island off the coast of Ellesmere Island in far northern Canada That day Walker built a small rock cairn and wrote a letter which he enclosed in a bottle and buried under the cairn In the letter he explained that he had placed the cairn exactly 168 3 feet 51 3 m from the edge of the glacier 1 He asked Ward Hunt Island and the nearby ice shelf have provided startling examples of melting Arctic ice 5

Melting Arctic Ice — page 3 — whoever found his letter to measure the distance to the edge of the glacier again and send the result to him at Ohio State University In 2013 biologist Dr Warwick Vincent and his colleague Denis Sarrazin discovered the bottle and letter Following Walker’s wish they measured the distance to the glacier They discovered it was now 401 feet 122 m away 2 In the 54 years since Walker first measured it the glacier had retreated 233 feet 71 m It was shrinking Walker did not live long enough to receive a response from Vincent He died the same year he wrote the letter He was only in his twenties But Vincent remarked on Walker’s brilliance in leaving this message for the future In the 1950s he says It was unthinkable that this would melt 3 Walker was one of the first scientists to realize that the climate was warming ice was melting and future glaciers might look very different His data point a comparison of glacier change over time is valuable Vincent said It is very old very rare and from an isolated location Vincent and Sarrazin decided to carry on the tradition They photographed Walker’s letter replaced it and added a letter of their own They asked the next finder to measure the distance to the glacier again and report back to them MEASURING ICE CHANGES Finding Walker’s decades-old letter was lucky but scientists do not rely only on luck to learn about ice melt and glacier retreat So how do they know glaciers and ice sheets are retreating How do they know sea ice is melting How do they know how fast it is happening One way is by using satellite imaging Satellites in orbit around Earth monitor 6

Melting Arctic Ice — page 4 — October 1986 September 2002 Satellite photos taken decades apart show changes in Alaska’s Bering Glacier glaciers ice sheets and icebergs When scientists compare images based on data taken at different times they can observe changes in the extent of ice 7

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