Yellowstone National Park is getting hotter. Average temperatures today are as high or higher than they have been at any point in the past 20,000 years and likely the past 800,000 years, as well.

Yellowstone National Park is famous for its beautiful but harsh winters. Blanketed in snow, it exudes an almost mythical aura—even in the season’s common subzero temperatures there. Now, however, a new study shows that the park’s summers are getting more severe, with August 2016 ranking as one of the hottest summers in the last 1,250 years.

However, scientists say that management changes on Western federal lands that would encourage more beavers and wolves could repair disturbances in ecological processes—the kind that extreme heat waves and extended droughts can cause.

And, surprisingly, wolves themselves just might hold the key to garnering support for environmental protection measures and securing funding to make forward-thinking and big-dream conservation projects come true.

Winter temperatures in Yellowstone range from zero to 20 degrees Fahrenheit throughout the day. Subzero temperatures are common, especially at night and at higher elevations. But the season does bring a singular beauty to the landscape. ©Eric Rock

Getting hotter in the GYE

Yellowstone National Park is getting hotter.

That may not be shocking, given today’s soaring global warming and climate change. But what is somewhat astonishing is that the 20th and 21st centuries—and especially the past 20 years—are the hottest in a new, 1,250-year record. Previously, temperature records for the Greater Yellowstone Ecosystem (GYE) were available only going back to 1905.

In findings that were recently published in the science journal Geophysical Research Letters, scientists using Blue Intensity (BI)—a new, cost-effective method for assessing tree-ring density—drew upon samples of living and dead Engelmann spruce trees collected at high elevations in and around Yellowstone National Park to officially extend the record of maximum summer temperatures back centuries beyond those recorded by instruments.

BI was developed in Europe in the early 2000s. Unlike traditional tree-ring methods, where annual or semiannual growth rings are measured, Blue Intensity assesses the outermost part of annual growth rings, called the “latewood,” which has been shown to correlate closely with maximum summer temperatures. Because of their uniformly light-colored wood, Engelmann spruce trees—which are found throughout North America from Canada to Mexico—are the perfect species for BI methods, which can be biased by color variations in wood samples. Engelmann spruce also live between 600 and 800 years and rot relatively slowly. The pristine setting of Yellowstone National Park provided an opportunity to source samples from living and downed trees dating back 1,250 years. In fact, the use of Blue Intensity in this study provided one of the few millennial-length temperature records for North America.


Blue Intensity is a new method that assesses tree-ring density. It provides crucial data for scientists seeking to better understand the relationships between increasing temperatures and environmental factors, such as fire regimens and seasonal snowpack.

The researchers found that the climate data gleaned from the tree-ring samples fits closely with the instrumental record over the past 100 years. They were also able to identify several known periods of warming, including the Medieval Climate Anomaly that occurred roughly between 750 and 1350, as well as several multidecadal periods of cooling prior to 1500.

The warm periods of the past were characterized by substantial temperature variations over decades, markedly different from the prolonged, intense warming trends seen over the past 20 years. In fact, the warming trend beginning around 2000 is the most intense in the record. That rate of warmth over a relatively short period of time is alarming and has important implications. It may spell trouble for the GYE, by exacerbating droughts, wildfires and other types of ecosystem stressors.

Rewilding in the West

Those ecological hardships might be helped by a new management proposal for Western federal lands: more beavers and wolves.

Gray wolves were hunted to near extinction in the West but were reintroduced to parts of the northern Rocky Mountains and the Southwest starting in the 1990s through measures made possible by the Endangered Species Act. ©Henry H. Holdsworth

Right now, much of the American West is going through an unprecedented period of converging crises, including extreme heat waves, loss of biodiversity, massive fires, and extended droughts and water scarcity. In a paper published in August 2022 in the journal BioScience titled Rewilding the American West, 20 scientists and authors suggest using portions of federal lands in 11 states to establish a network based on potential habitat for the gray wolf, the apex predator who’s able to trigger powerful, widespread ecological effects by naturally controlling native ungulates and by facilitating regrowth of vegetation species, such as aspen, which is declining in the West and supports diverse animal and plant communities.

In those 11 states, the authors identified areas—each at least 1,930 square miles—of contiguous, federally managed lands containing prime wolf habitat. The states in the proposed, 193,051-square-mile Western Rewilding Network are: Arizona, California, Colorado, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, Washington and Wyoming.

The gray wolf’s current range in those 11 states is only about 14 percent of what it was historically. While gray wolves probably once numbered in the tens of thousands, today there may be only 3,500 wolves scattered across the entire West.


Today, beavers are widely distributed across the U.S. Their dams provide them with protection from predators, but the impacts of their dam-building can occasionally bring them into conflict with humans.

Beaver populations, too, declined after settler colonialism, by roughly 90 percent. Today, beavers are nonexistent in many streams, meaning the loss of their ecosystem services. By felling shrubs and trees and constructing dams, beavers enrich fish habitats, increase water and sediment retention, maintain water flows during droughts, improve water quality, increase carbon sequestration and generally improve habitats for riparian animals and plants. While riparian areas occupy less than 2 percent of the land in the West, they provide habitat for up to 70 percent of the wildlife species. Reintroducing beavers, then, would be a cost-effective means of repair.

The BioScience paper includes a catalogue of 92 threatened and endangered animal and plant species that have at least 10 percent of their ranges within the proposed Western Rewilding Network. For each of those species, threats from human activities were examined. The most common of those dangers, say the authors, is livestock grazing, which can cause stream and wetland degradation, affect fire regimens and make it harder for woody species, especially willows, to regenerate.

Rewilding, of course, is most effective when all stakeholders are encouraged to participate and are considered, including Indigenous peoples and their governments.

The Western Rewilding Network is an ambitious plan that just might work.

Public Domain

Despite our clashes with beavers, they perform valuable ecological services. Their ponds act as firebreaks, filter out pollution, reduce erosion, slow down floods, and store water for use by farms and ranches.

Mainstreaming in the Y2Y

Getting buy-in for such ambitious conservation plans, however, is always a challenge. But unexpectedly, gray wolves themselves can be of help there, too.

In 1991, a female gray wolf wearing a radio collar set off on a journey through the Rocky Mountains. In just nine months, she traversed more than 38,000 square miles that encompass three U.S. states and two Canadian provinces. When a slightly fictionalized version of her adventure was portrayed in the 1999 opening season of the television show The West Wing, the five-year-old wolf, dubbed “Pluie,” captured the public’s attention.

Now, say scientists in a paper published in the journal Conservation Science and Practice in December 2021, a movement inspired partly by Pluie’s journey is showing the potential gains that can come from enterprising, publicity-friendly but assertive conservation projects that involve charismatic animals, such as wolves.


Nearly three decades after its inception, the Yellowstone to Yukon project has coincided with a surge in land protections there compared with other areas, as well as an uptick in funding and an unmatched network of road crossings for animals.

While certain conservation initiatives might earn headlines (and a mention on a popular TV drama), it’s less clear how much of a difference they make on the ground. For example, it’s hard to draw causal links between conservation campaigns and changes in the population size of an endangered species.

Wanting to find out if such publicity-friendly endeavors do, indeed, matter, a University of Montana researcher teamed up with scientists from the nonprofit leading the Yellowstone to Yukon (Y2Y) campaign to find data that could help answer whether media hype translates into practical results.

In the early 1990s, the Y2Y campaign was one of the first of its kind. A broad coalition of organizations joined to push for an interconnected system of wildlands stretching across much of a continent: from the Canadian Yukon to Yellowstone National Park in Montana and Wyoming. The goal was to accommodate the needs of large, wide-ranging carnivores, including grizzly bears and wolves.


The Y2Y approach is a blueprint for biodiversity conservation around the world. It has played a large role in the growing numbers of threatened grizzly bears.

To assess the successfulness of the media-friendly Yukon to Yellowstone initiative, the scientists looked at how this region fared compared to similar places elsewhere. Results showed that the Y2Y area stood out, gaining more than 38,610 square miles of protected lands between 1993 and 2018, an increase of 7.8 percent, to a total of 17.6 percent stretching from the remote Peel River in the northern reaches of the Yukon Territory south to the geysers of Yellowstone. By contrast, protections in those same states and provinces but outside the reach of Y2Y increased by only 2 percent. That slower growth matched the increase in protected areas throughout North America over the same time.

The Y2Y area was unique in other ways, as well. Grizzly numbers in parts of the U.S. included in the Y2Y program grew from 400 to at least 1,700, prompting a legal fight over whether they were so numerous that they no longer needed protection under the Endangered Species Act. The Y2Y campaign also helped spur the creation of 117 structures—such as bridges and tunnels—that help wildlife cross roads that interfere with migration and isolate different animal populations. The Y2Y region now has the highest concentration of such crossings anywhere in the world.

There were other media mentions, too. A 2000 National Geographic book titled Yellowstone to Yukon described the region’s ecosystems and the threats they faced. Y2Y was mentioned in the television hospital drama Grey’s Anatomy. The researchers counted nearly 100 scientific papers and 67 books that referenced the Y2Y concept. The large-landscape conservation idea, specifically in the Yellowstone to Yukon region, was being mainstreamed into public consciousness.

The range of one wandering wolf who managed to capture the public’s attention translated into big gains for habitat conservation. ©Henry H. Holdsworth

Learning in the Anthropocene

Many peoples throughout the world respect and think very positively of wolves. Because wolves retreated into the mountains and hills to get away from humans, some tribal peoples of California and the Great Plains connected wolves to high places (or the spirit). In the Lakota language, the word for wolf, sunkmanitu, means “divine dog.”

Others saw the wolf as a teacher-animal.

Once again, I think, wolves are showing us the most productive and least destructive way of living on and with the land. Perhaps we need to pay more attention to their lessons.

Here’s to finding your true places and natural habitats,