Matthew Sturm takes aerial photos of the changing Alaskan landscape.

No single study has galvanized Arctic scientists like the shrub photography project, led by Matthew Sturm of the Army Corps of Engineers' Cold Regions Research Laboratory. The study offers clear visual evidence that Alaska is changing, and changing fast.

Re-shooting areas originally photographed by the military in the 1940s, the team has made 270 nearly exact matches that show that across thousands of miles of the North Slope, the tundra has gotten 30 to 40 percent shrubbier. Long-term experiments at Toolik Lake field station have shown that a warming climate favors shrubs like alder and willow over tundra grasses, moss and lichens.

Scientists measure the carbon dioxide in the tundra. From this they can infer that the climate is indeed warming.

This change is important because shrubs in winter trap snow, which insulates the land, making it warmer. And if they stick up above the snow, shrubs also make the land darker, so it reflects less heat. So if shrubs continue to flourish on the tundra, Sturm explains, the whole Arctic system will begin to change.

Taken together, the changes now apparent in Alaska have profound implications not just for the north, but for the climate of the globe. Right now scientists can't say exactly where things are headed, but it's clearly to somewhere new in human experience.