ANCHORAGE - Photos of North Slope tundra taken in the 1940s are dramatically different from photos of the same areas taken more than 50 years later.
Scientists say that's evidence of a greening Arctic landscape, possibly because of a warming climate.
The international science journal Nature recently reported on the findings of the scientists who studied the two sets of photographs.
The old photos - about 3,000 images of the North Slope landscape - were taken more than half a century ago in a search for oil, according to a program on Arctic Science Journeys, a radio service of the Alaska Sea Grant College Program and the University of Alaska Fairbanks.
Matthew Sturm of the U.S. Army's Cold Regions Research and Engineering Laboratory in Fairbanks, who was studying shrub growth in the Arctic, learned of the photos by chance. When he finally tracked them to an office of the U.S. Geological Society in Anchorage, he learned they were slated for disposal.
The USGS sent Sturm boxes full of high-resolution prints.
The oil-seeking scientists had flown about 1,200 feet above the ground and had photographed "virtually every creek and drainage you can imagine" in a swath of land several hundred miles wide and about 200 miles north to south, Sturm said.
He and two other scientists picked 66 of the clearest images and set out to find the identical areas.
After a painstaking process, they rephotographed the scenes in 2000 and compared the photos. The difference was remarkable.
What were only patches of shrubs 50 years ago are now denser, Sturm said.
Moderate to significant shrub growth was evident in more than half the sites, while no site showed a decrease in shrub abundance or density, said Sturm.