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Extreme event or climate change? Experts weigh in on Colorado weather – Coloradoan


Be it a downpour during a drought or a cool spell during the heat of summer, just about any weather anomaly these days has people pointing out it was either caused by climate change or proves climate change isn’t real.

Oh, if it was just that simple.

This we know from scientific research in Colorado, according to the National Oceanic and Atmospheric Administration’s 2022 Colorado climate summary:

  • Temperatures here have risen about 2.5 degrees Fahrenheit since the beginning of the 20th century, and warming has occurred in all four seasons with very hot days (95 degrees and warmer) occurring above average since 2000.
  • Future changes in annual precipitation are uncertain, but warming temperatures are expected to exacerbate the recent trend of reduced overall water availability and earlier snowmelt and runoff.
  • Severe droughts have occurred in recent years and projected evaporation of soil moisture during dry spells will increase the intensity of naturally occurring droughts and result in an increase in the frequency and severity of wildfires. 

The questions is: Do those elements of climate change have a direct correlation to, say, our 2013 flood, 2019 bomb cyclone or 2020 Cameron Peak Fire?

We asked local experts about how climate change contributes to extreme events as well as how climate change has and will impact Colorado.  

People seek refuge in the Mountain Ave. parking garage as rain moves in during Bohemian Nights at NewWestFest in 2016.

How baseball can explain climate change’s influence

Scott Denning, a climate scientist and professor of atmospheric science at Colorado State University, said he uses a baseball analogy to explain how climate change works.

Basically, pitches are the weather. The batting average is climate. Steroids represent carbon dioxide.

Denning said a batting average is built pitch by pitch depending on the number of hits and outs you make. Over a long period of time, the batting average shows a trend. That’s climate change.

Now, say the player starts using steroids and his batting average goes up. If one day he hits a home run, it is difficult to attribute that one home run to steroids. But if the batter starts hitting significantly more home runs, you likely believe the change is due to the steroids.

Scott Denning

“It has been shown that we have more 90-degree and 100-degree days in Colorado than we used to,” said Denning, who has 30 years of experience as a climate scientist. “That is a trend, or the batting average. If we have a extremely hot day, it’s silly to say that climate change caused it to be hot. But rather it is hot more often because carbon dioxide in the atmosphere results in the average temperature to go up.

“So imagine if steroid-deniers said you can’t blame steroids for the batter hitting a home run. You can’t if it is just one home run, but you can if he hits a home run 50% more after taking steroids.”

Colorado wildfires: Officials prepare with funding, preparedness 

How climate change influences Colorado’s temperature, precipitation  

The worldwide climate change trend is for a warmer world, which is why climate change was initially referred to as global warming. 

But global warming is only a part of climate change. Precipitation is another major part. And while in Colorado and elsewhere the forecast heavily favors a continued warming trend, precipitation forecasts are more complicated.

Since 2000, Colorado has experienced the highest summer and spring average temperatures in the historical record dating to 1900, according to the National Oceanic and Atmospheric Administration’s 2022 Colorado climate summary.

The state’s highest temperature on record, 115 degrees, was set at John Martin Reservoir in southeastern Colorado on July 20, 2019.

While scientists can’t say that record was caused by climate change, they can say climate change contributed to the record. 

“We always will have fluky weather, but there clearly is a trend for temperatures rising,” Denning said. “You can say average temperature has gone up, but more importantly the frequency of extremely hot weather has increased as well and that will consistently lead to more drought, wildfires and earlier runoff of snowmelt.”

City climate goals:As Fort Collins faces funding gap, priorities on climate and affordable housing raise questions

Climate change’s influence on precipitation is less clear because modeling trends show areas that historically receive more moisture are receiving or will likely receive more moisture, while more arid areas are receiving or will receive less moisture.

The National Oceanic and Atmospheric Administration’s 2022 Colorado climate summary stated: “Although projections of overall annual precipitation are uncertain, precipitation is projected to increase in the winter and possibly decrease in the summer.”

It also stated that unlike many areas of the country, Colorado and other southwestern states have not experienced an upward trend in the frequency of heavy precipitation events.

In Colorado and many southwestern states, there is a trend in reduced snowpack. Denning looked at 800 different SNOTEL sites − SNOTEL is an automated system of snowpack and related climate sensors operated by the Natural Resources Conservation Service − across the West over the last 40 years.

He said average snowpack at hundreds of sites had fallen by half. In Colorado, there is a lessening of snowpack in the southern mountains compared to the historical average, but that distinction is not as prevalent in the state’s northern mountains.

The U.S. Global Research Program’s report said snowpack has decreased since the 1950s in Colorado, due to earlier melting and less precipitation falling as snow, resulting in April snowpack declining by 20% to 60% at most monitoring sites in the state.

The timing of precipitation is also changing in Colorado. The NOAA report said Colorado has experienced mostly above-average fall precipitation since 1980 and below-average spring precipitation since 2000 in comparison to averages since 1900.

It’s not that we don’t still receive spring blizzards. Fort Collins received more than 20 inches of wet, heavy snow in March 2021, and we had the March 2019 bomb cyclone blizzard. We simply receive fewer of those.

Cars exit I-25 at the Wellington exit during the bomb cyclone blizzard on March 13, 2019.

The changing timing of precipitation creates other issues.

Warmer autumns mean less precipitation falls as snow and more as rain in the mountains. While that might sound like an even proposition, that results in less snowpack, which is the major water supply for much of the West.

With less snowpack combined with warmer spring temperatures and less spring snow, snowmelt runoff is occurring nearly two weeks sooner than the long-term average. That impacts movement of water to farmers and municipalities, which can disrupt irrigation and water supplies.

“There is a lot of natural variability, but we do know for certain one of the stronger signals with climate change is we are seeing warmer falls into early winter,” said Becky Bolinger, assistant state climatologist. “We have always had drought in Colorado and the West, but with climate change it means we are at higher risk for more frequent drought, some of which could be severe and prolonged.”

Combined with drier soils caused by higher temperatures, that increases soil evaporation. In some locations, the combination of dry soils and persistent lower-than-average precipitation means more of the precipitation that does fall soaks into the soil before it reaches our rivers, which reduces flows to fill reservoirs.

This impacts water users downriver of Colorado, which is at the headwaters of four major rivers, including the Colorado River, that supply water to 18 downriver states.

The desert Southwest is in the throes of a megadrought that has lasted more than 20 years, recording its driest 22-year period in at least 1,200 years, according to a UCLA-led study published in the journal Nature Climate Change. The study said the megadrought has been strongly influenced by human-caused climate change.

The Cameron Peak Fire burn area is pictured in the Big Thompson watershed area near Dunraven Glade Trailhead east of Glen Haven on Oct. 6, 2021.

Colorado wildfires and climate change

In 2020, Colorado experienced its largest wildfire season with the three largest wildfires in state history — Cameron Peak, East Troublesome and Pine Gulch fires — collectively burning more than 540,000 acres and costing roughly $150 million in fire suppression alone.

In late December 2021, the Marshall Fire destroyed 1,084 homes in Superior and Louisville, resulting in more than $500 million in losses, the largest loss from a grassfire in state history. 

Were those fires caused by climate change or simply chance?

That’s a complicated question. 

Colorado’s wildfire season is lengthening due to warmer temperatures and snowmelt runoff occurring earlier, which leaves the forests drier longer and more susceptible to fires. Some fire and forest experts also say forest management plays a role in exacerbating fires such as the Cameron Peak and East Troublesome fires.

Forest management:Cameron Peak, East Troublesome fires reignite debate

The late summers and falls of 2020 and 2021 were especially hot, dry and windy, leading to a higher fire risk. The Pine Gulch Fire, the only one of those fires started by lightning, started July 31. The Cameron Peak Fire (presumed but not confirmed to be human-caused) started Aug. 13, the East Troublesome Fire (recently confirmed to be human-caused) on Oct. 14 and the Marshall Fire (presumed but not confirmed to be caused by arcing power lines) on Dec. 30.

During the Cameron Peak Fire, two significant snow events occurred. On Sept. 8, 2020, just days after near-record heat, 8 to 14 inches of snow fell on the fire.

Then, on Oct. 24-25, a winter storm dropped 8 to 18 inches of snow on the fire, which greatly helped firefighters contain it.

Previous coverage: RMNP fire official was ‘absolutely sure’ Estes Park was going to burn

Two snow events that go against the climate change trend of less snow in fall saved the Cameron Peak Fire from being even more destructive. 

Still, Bolinger believes the chances are an increase in number and severity of wildfire seasons like we saw in 2020 and 2021 could become more normal than an anomaly with climate change.

“My gut feeling is this is what we can expect more often and that these were not just a complete fluke,” she said. “My hope is that, in the case of the Marshall Fire, this is something we can plan for and address because there are a lot of people who live in the wildland-urban interface.”

Reporter Miles Blumhardt looks for stories that impact your life. Be it news, outdoors, sports — you name it, he wants to report it. Have a story idea? Contact him at milesblumhardt@coloradoan.com or on Twitter @MilesBlumhardt.

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