The boreal forest wraps around the globe at the top of the Northern Hemisphere in North America and Eurasia. Also known as taiga or snow forest, this landscape is characterized by its long, cold and snowy winters. In North America it extends from the Arctic Circle of northern Canada and Alaska down into the very northern tip of the United States in Idaho, Washington, Montana, and Minnesota. It’s the planet’s single largest biome and makes up 30 percent of the globe’s forest cover.

Moose are the largest ungulate in the boreal, adapted with their long legs to wade in its abundant marshes, lakes and rivers eating willows, aspen and other plants. In the southern boreal forest of northern Minnesota, moose were once plentiful, but their population has plummeted. Thirty years ago, in the northwest part of the state, there were some 4,000; they now number about a hundred. In the northeast part, they have dropped from almost 9,000 to 4,300. They’ve fallen so far, so fast that some groups want them listed as endangered in the Midwest.

Moose carcasses deteriorate rapidly before they are found, and so forensics has not been able to determine why they are dying. Some experts surmise it could be that tens of thousands of ticks that mob an animal and weaken it. Others think it’s a parasite called liver flukes, or the fact that winters have gotten so warm the animals can’t regulate their body temperature and die from heat stress.

But Dennis Murray, a professor of ecology at Trent University in Peterborough, Ontario, thinks the dying moose of Minnesota and New Hampshire and elsewhere are one symptom of something far bigger – a giant forest ecosystem that is rapidly shrinking, dying, and otherwise changing. “The boreal forest is breaking apart,” he says. “The question is what will replace it?”

Many scientists, in fact, are deeply concerned about the state of the world’s largest forest. The Arctic and the boreal region are warming twice as fast as other parts of the world. Permafrost is thawing and even burning, fires are burning unprecedented acres of forest, and insect outbreaks have gobbled up increasing numbers of trees. Climate zones are moving north ten times faster than forests can migrate. And this comes on top of increased industrial development of the boreal, from logging to oil and gas. The same phenomena are seen in Russia, Scandanavia, and Finland.

These disturbing signals of a forest in steep decline are why NASA just launched a large-scale research project called ABoVE — Arctic Boreal Vulnerability Experiment, a “major field campaign” with 21 field projects over the next decade. But the studies will confirm in detail what many know is well underway.

“Boreal forests have a potential to hit a tipping point this century,” said Anatoly Shvidenko, of the International Institute for Applied Systems Analysis and a co-author of a survey of a recent research on boreal forests in the journal Science. “It is urgent we place more focus on climate mitigation and adaptation with respect to these forests.”