In 1997, the U.S. Geological Survey embarked on the Repeat Photography Project, a systematic method of studying climate change and global warming based on glacier retreat in Glacier National Park, Montana. Computer models predict that all the glaciers in the Park will melt by 2030 under current warming trends.

The Repeat Photography Project compares historic photos taken by the park's early photographers (including Morton Elrod, T.J. Hileman, Ted Marble, and F.E. Matthes) and makes a side-by-side comparison with contemporary photos. Copies of the old photos are taken into the field in order to determine the exact vantage points of the original images, and the photography is done within a precise window of time when the previous winter's snow has melted and only glacial ice remains. The historic images were taken by park photographers as a way to publicize the natural beauty of the park and earn a living, but they now serve as dramatic evidence of our changing climate.

Here are 8 side-by-side images that give a stark representation of global warming's effects on our cold climates.

Top: The Chaney Glacier in Glacier National Park, Montana. Above, right: The red dots on this map represent selected repeat photographs of glaciers taken throughout Glacier National Park. For more information about the USGS Repeat Photography Project, visit www.nrmsc.usgs.gov.