Colorado’s scorching summer of 2018 may signal a new normal.
Best-case scenarios show 100-degree days becoming seven times more common in coming decades, while worst-case scenarios show temperatures topping the century mark on roughly 10 percent of days by 2080.
Much of this depends on the near-future global efforts to reduce emissions and stem global warming, but Colorado climate scientists are clear that emissions cuts won’t determine whether extreme heat becomes more common in the state, but how much more common.
On July 11, Denver had its 30th day of 2018 at 90 degrees Fahrenheit or higher. That mark had never previously been crossed so early in the year.
But, Stephen Saunders of the Rocky Mountain Climate Organization, warned, “What we’ve seen so far is probably only a small taste of what lies ahead of us.”
Saunders was the lead author on a series of recent studies examining extreme heat scenarios in various segments of Colorado’s Front Range, including Denver, Boulder County and Larimer County.
Those studies, conducted in 2016 and 2017 and funded by the Colorado Department of Local Affairs and the Denver Department of Public Health and Environment, present some almost unfathomably scorching scenarios.
For example: At the current rate of global emissions, Denver will see 25 days per year above 100 degrees by mid-century during extreme summers, like the current one, the researchers found.
It’s unlikely, though, that the current rate will be maintained. Every country in the world, other than the United States, is signed onto the 2015 Paris agreement, which calls on individual nations to voluntarily work to reduce their own greenhouse gas emissions.
The central goal of the Paris agreement is, as the United Nations puts it, “to strengthen the global response to the threat of climate change by keeping global temperature rise this century well below 2 degrees Celsius (3.6 degrees Fahrenheit) … and to pursue efforts to limit the temperature increase even further to 1.5 degrees Celsius.”
Saunders’s team wondered just how much hotter Colorado would get if the 2-degree Paris goal is reached.
On average, the state will see 2 days per year with temperatures over 100, they found, under a scenario of enormous global success in limiting emissions. That might not sound like too many extra-hot days every year, but consider that over the past century, Colorado’s averaged only one day above 100 every three years, roughly.
Kevin Trenberth, who holds the title of distinguished senior scientist at Boulder’s National Center for Atmospheric Research, isn’t optimistic that the world will achieve the Paris goals.
“I personally think there’s no way that’s going to happen,” he said of the goal to limit temperature increase to 1.5 degrees Celsius, “and I think it’s very unlikely we meet 2 degrees Celsius. I think we’ll zoom right by that around 2050.”
The United States’s lack of formal participation in the Paris accord — a reversal by President Trump of the country’s Obama-era course, inspired many cities and states, including Denver, to commit to their own, local 2050 emissions targets. But, Trenberth said, that’s likely not enough.
The U.S. has, over time, produced far more heat-trapping pollution than any other nation, according to the Environmental Protection Agency.
It’s fallen behind China in annual pollution, but in overall emissions, remains above everyone else. And while the country is economically, intellectually and industrially capable of dramatically shifting focus toward lowering emissions, its present administration has rarely even acknowledged the existence of human-caused climate change, much less taken steps to lead on the issue.
“It’s been very hard to get across to the general public and to politicians that we can’t simply turn back the clock very easily on this issue,” Trenberth said. “There are long-term consequences.”
Trenberth explains how he sees these consequences playing out:
There is more heat beating down on our planet than can escape the atmosphere because of the blanket of greenhouse gases the U.S. helped knit. That blanket prevents heat from going out to space.
So, the temperature goes up, on average, and the added heat means moisture evaporates more quickly. In turn, the extra water in the atmosphere fuels storms that are heavier and more vigorous than those we’ve historically seen.
And, in the places it’s not raining, the heat saps needed moisture and the risk of wildfire goes up.
This summer in Colorado already has seen a point at which eight different wildfires were burning at once. Gov. John Hickenlooper said this week that the state’s now over budget for addressing wildfires.
And if our current June and July become the norm, Coloradans can come to expect worse fire seasons and government budgets unequipped to keep pace.
“We can avoid a really fundamental transition of our climate if we reduce emissions,” Saunders said. “But that takes our entire planet doing it.”