In the worst-case scenario, resort communities along the Interstate 70 mountain corridor will become much hotter during the coming decades.

And the best-case scenario? Warmer, inevitably, because of greenhouse gas emissions already in the atmosphere, but not nearly as much, and then tapering off after 2040 if emissions can be reduced dramatically.

These bookend conclusions apply to both Eagle and Summit counties in parallel studies released Monday, Aug. 23. The studies by the Rocky Mountain Climate Organization were commissioned by the two counties and, in the case of Summit County, two of its towns: Frisco and Breckenridge.

Eagle County Commissioner Kathy Chandler-Henry said nothing in the reports particularly surprised her. Previous climate studies have painted the picture broadly of what to expect. But the study — for which Eagle County paid $15,000 — delivers a level of detail for the two counties not previously available.

As a child and young woman in Eagle, Chandler-Henry remembers many days of 30 below zero temperatures or colder. In summers, it often got into the 80s, even the 90s.

“But it never got to nearly 100 degrees as it did in June,” she said.

By late in the 21st century, high summer temperatures could average 100 degrees at Eagle, and highs of 106 could occur if the worst scenario unfolds.

That high-emissions scenario sees atmospheric concentration of carbon dioxide, now at 420 parts per million, hitting 600 ppm in the coming decades. Scientists think this no-action scenario is unlikely, partly because action is now underway, but they haven’t entirely discounted it.

The studies examine what might happen with three lesser levels of emissions. Even then, a typical year in the next two decades might resemble that of 2020, a notoriously warm year, with continued warming through the 21st century but less so than the extreme scenario.

And if the global community can actually slow the growth of emissions? Bad news for a while, as continued warming is baked into the climate system by existing atmospheric pollution. The Avon-Edwards area, for example, is likely to be 3 degrees warmer in 2040 as compared with the baseline of 1970 to 1999. But taking dramatic action globally, the heating will level off.

In Summit County, the directions are the same, but the numbers are lower. Again, much depends on whether the global community tames emissions and by how much. Again, hotter summers are in the cards. At the extreme, there would be 54 days in the Frisco-Breckenridge area by century’s end with temperatures above 80 degrees. That compares with only four days in the baseline period of 1970 to 1999.

Summit County Commissioner Joshua Blanchard said the study data “tell us our climate action goals are important and that we need to accelerate them.” He called climate change a “threat to our way of life as well as our economy and our environment.”

Impacts on recreation

Stephen Saunders, the lead author of the reports, said the takeaway message of the studies is the need for immediate and vigorous action to reduce emissions.

“Unless we quickly and sharply reduce emissions, in about 20 years, the mountains will become unrecognizably and unacceptably hot,” he said.

Climate models for decades have struggled to replicate the rugged topography of Colorado and other mountainous areas in their computer modeling. Modeling has improved in the past decade, but the Gore and Tenmile ranges pose challenges that Kansas or Missouri, for example, do not.

Getting a sharper bead on the very local level provides value to community planners, said Torie Jarvis, who directs water quality and quantity planning for the Silverthorne-based Northwest Colorado Council of Governments, one of the sponsoring agencies of the two studies.

“From our perspective, for a recreational economy, including the impact of warming fisheries, this is a concern,” she said.

This year’s higher temperatures, which forced some river segments to be closed, provide a glimpse of the future.

Jarvis hopes the study also aids visualization of changes that broader climate change projections, including the report issued by the International Panel on Climate Change in August, cannot.

“For me, I can visualize a very specific temperature, such as Frisco getting to 85 degrees for multiple months, more easily than reading about projections of an increase of 3 degrees in the next 50 years,” she said.

The two reports also examine precipitation, which climate models have more difficulty in predicting than temperature because models fail to do a good job of simulating monsoonal thunderstorms that drive much of Colorado’s summer precipitation. Still, the models generally agree that total annual precipitation amounts will increase somewhat, perhaps 10% or less. This is because warmer atmospheres have greater capacity to hold water.

This increase in precipitation is most likely to occur during winter. One study scenario, for example, projects 7% more precipitation on Vail Mountain. Keep in mind that April temperatures rarely yield powdery snow, so expect mushy conditions more frequently through ski season.

More snow and rain do not necessarily translate into more water in creeks and reservoirs. Increased heat means more evaporation and transpiration overlapped with drought, which is causing conniptions in the Colorado River basin.

In Vail, that could be a problem for Gore Creek, which already struggles to maintain its status as a gold medal trout fishery, said Kristen Bertuglia, the town’s environmental sustainability director.

Bertuglia always points out another implication to increased warming. Already, air conditioning — something unthinkable in the 1970s — has become a must-have in new construction in Vail and the Eagle Valley. This may well cause a shift in electrical demand, making Vail more like Denver. Instead of peak electrical demand occurring on winter evenings, as now occurs, the peak demand could shift to summer afternoons.

Those involved say these studies provide a strong case for taking action to cut emissions and adapt to the changing climate.

“They help spur action,” said Boulder County Commissioner Matt Jones, who worked in the Summit County ski industry in the late 1970s, later becoming a state legislator.

Boulder and Boulder County in 2016 also commissioned the Rocky Mountain Climate Organization to conduct a similar study. Susie Strife — director of sustainability, climate action and resilience for Boulder County — said the more localized analysis of future climate conditions has helped galvanize climate action. One indirect result was creation of an advocacy organization called Colorado Communities for Climate Action, which now has 38 local jurisdictions. The organization has become a reliable presence in testimony before legislative committees.

Thinking foremost locally if also globally, Vail is now studying how to tame the emissions from its snowmelt systems. The municipality has 13 acres of snowmelt areas in Vail Village, Lionshead and other areas heated by the combustion of natural gas. It’s the single largest contribution to greenhouse emissions, even more than the town’s fleet of buses.

Allen Best publishes Big Pivots, an e-journal focused on the energy and other transitions forced by climate change. See more at BigPivots.com.