The impacts of climate change on the state are deep and span a range of issues; but the top five predominant effects are summarized below, with links to further information. This page will be updated as necessary.
More frequent and more severe wildfires
More frequent and more severe wildfires
If someone were to ask a Coloradan whether they’d witnessed climate change in the past five years, the obvious answer would be: yes, of course, the wildfires have gotten progressively more devastating. The mechanism behind this is that climate change has caused record high temperatures and record dry conditions. Warm, dry conditions enable wildfires to spread more easily, make them harder to put out, and also contribute to the spread of various bark beetles, which kill off trees and make it harder for forests to regenerate. Warmer, drier conditions lasting into the fall and winter months have also extended the length of the fire season. The Colorado Climate Change Vulnerability Study indicates that wildfires will likely become both more frequent and more severe in the coming years. In the first two decades of the twenty-first century, Colorado has seen some of its hottest years on record, and has experienced the most severe droughts on record. In the summer of 2021, two heat waves broke temperature records across the state, from Denver to Grand Junction. The second half of 2021 was the warmest and driest on record for the Front Range, and then, on December 30, Colorado saw its most destructive wildfire on record: the Marshall Fire, which destroyed more than 1,000 buildings, including at least 600 homes. 2020, which was also one of Colorado’s warmest and driest years on record, brought the three largest wildfires in Colorado history: the Cameron Peak Fire near Fort Collins, the East Troublesome Fire near Estes Park, and the Pine Gulch Fire near Grand Junction. The ten largest wildfires in Colorado history have all been in the past 20 years. In addition to property damage, forest destruction, and worsening air quality, wildfires in Colorado have had cascading impacts that have damaged local ecosystems, decimated animal and plant populations, and devastated local economies that are dependent on recreation and tourism. Wildfires destabilize root systems, which act as important barriers to soil erosion. For this reason, areas scorched by wildfires are vulnerable to rockslides and landslides for years following the fire. For instance, in the summer following the Grizzly Creek Fire near Glenwood Springs, rain events triggered debris flows on several occasions, which closed the I-70 corridor several times and caused billions of dollars in structural damage. One rockslide – which officials called a “500-year-event” – was so powerful that it diverted the flow of the Colorado River, created a dam in the river, and closed the highway for more than two weeks, having an unfathomable toll on the local economy, which is largely tourism-dependent, particularly in the summer months. Wildfires also create conditions more suitable for insect outbreaks, pathogen invasions, and the spread of non-native plant species, which affects the entire ecosystem.More intense droughts
The American West is currently in the grips of one of the worst droughts in human history – a 20-year “megadrought” – and Colorado is no exception to that trend. Climate change creates drought by leading to warmer temperatures (through the Greenhouse Effect), which enhances evaporation, drying out soils and vegetation and reducing surface water. Warmer temperatures also make it so more seasonal precipitation falls as rain rather than snow, which is important in Colorado, where populations depend on melted snowpack for freshwater. However, warmer temperatures do not uniformly lead to drought, as climate deniers pointing to extreme rain events will be quick to mention. Instead, as the world warms, there is a pattern of traditionally wet places getting wetter, and dry places getting drier, as climate change amplifies the water cycle, leading to less precipitation in arid regions and more severe precipitation events in wetter areas. To make matters worse, increased evaporation means that warmer temperatures will limit the water supply, even with the same amount of rain. For instance, even if precipitation stayed constant, 2 degrees Celsius of warming in California would reduce the water supply for 25 million people by 15 percent.
In January 2021, according to the five-category U.S. Drought Monitor, 100 percent of Colorado was “abnormally dry,” with 88 percent in at least “moderate drought,” including 66 percent in “severe drought.” In the summer months, drought is even more severe.. Drought has been particularly pronounced on the Western side of the state – the Western Slope – which has been in a vicious cycle of hot and dry summers, which decreases agricultural yields. 2021 was one of the driest planting seasons in Colorado of the past 20 years.
2017 saw the lowest average snowpack in nearly 40 years. Both 2020 and 2021 were exceptionally dry years for Colorado. From January 2020 to August 2021, the Southwest – which includes Colorado – saw the lowest amount of total precipitation on record. After its latest first snow on record, in the second half of 2021, Denver saw the least precipitation on record by over an inch, which, coupled with record heat, created a perfect storm of conditions that enabled the Marshall Fire to devastate neighboring Louisville and Superior.
In 2021, the U.S. declared the first-ever water shortage on the Colorado River, because water levels in Lake Mead dropped so low that the reservoir would not be able to meet the water and energy needs of communities throughout the West. In 2021, both Lake Mead and Lake Powell – the second-largest water reservoir in the U.S. – dropped to their lowest levels on record.
Warmer temperatures
Not unlike the rest of the U.S., Colorado has set heat records in recent years due to climate change. Since warming of the atmosphere is the root cause from which several other effects of climate change stem, it is important to understand the mechanisms that underlie warming. Essentially, while about 30 percent of solar energy is reflected back into space, about 70 percent passes through the atmosphere to the Earth’s surface, and then about 90 percent is radiated back up to the atmosphere. Naturally occurring greenhouse gases (like carbon dioxide and methane) then trap the heat in the atmosphere, which is the reason why the Earth stays at a comfortable average of 59 degrees Fahrenheit. However, humans consuming fossil fuels – coal, oil, and gas – since industrialization have led to unprecedented levels of greenhouse gases in the atmosphere, which has led to unprecedented warming. While the carbon dioxide emitted on Earth used to roughly equal the amount absorbed by “carbon sinks” like oceans and trees, since the Industrial Revolution, carbon emissions have rapidly accelerated. This trend means both a higher average temperature and a higher frequency of heat waves.
Indeed, Colorado temperature records in recent years paint an increasingly dismal picture. The second half of 2021 was, by far and away, the hottest 6 months on record for Colorado, with an average statewide temperature that was 4 degrees Fahrenheit higher than average. 7 of Colorado’s hottest 10 years on record have taken place within the past 10 years: 2021 was Colorado fourth warmest year on record, 2017 was its third warmest , 2016 was its fifth warmest, and 2020 was its seventh warmest.
In June and then July 2021, Colorado faced two blistering heat waves that set record high temperatures across the state, including in Grand Junction, Pueblo, Alamosa, Hayden, Denver, and Colorado Springs. Indeed, the hottest three summers in Denver history have all been in the past 10 years: 2012, 2020, and 2021. Denver now averages 17 more days of 95-degree-plus temperatures every summer than in 1970. In fact, the five years during which Denver experienced the most 95-degree-plus days are all within the past 20 years: 2006, 2018, 2012, 2020, and 2021. In 2017, Colorado saw both its earliest and latest 80 degree days in history, indicating the effect climate change has had in effectively shrinking the length of the winter season.
Declining snowpack
In recent years, warmer temperatures have both increased the amount of evaporation in Colorado and decreased the amount of overall precipitation. Additionally, warmer temperatures have led to more precipitation falling as rain rather than snow. Since snowmelt feeds most rivers in Colorado, rivers across the state have seen water supplies dwindling to record lows in recent years. This is concerning, since snowpack is the source of most of Colorado’s water supply. Snowpack in Colorado acts like a drip irrigation system: snowpack peaks at around April 1 each year, and then as temperatures warm, snow melts, first saturating the ground and then flowing through rivers. If the snowmelt starts dripping earlier in the season, that in turn decreases the amount of runoff to flow through the ground, and limits water for the growing season.
Indeed, that is precisely the story here in Colorado: the Colorado River’s annual average flow has declined by about 20 percent since the twentieth century, half of which scientists have attributed to warmer temperatures. Scientists link this 1.5 billion ton reduction in water to Colorado’s snowpack both shrinking and melting earlier. Since snow reflects the sun’s heat back into the atmosphere, a reduction in snow leads to a feedback loop which, in turn, leads to more warming and less snow, melted earlier. One study found that snowmelt before April 1 has increased at half of the weather stations studied – throughout Colorado and the Western U.S. – which has decreased water supply during the warm season. Another recent study found that, for every 1 degree Celsius of warming, dwindling snowpack has caused the Colorado River annual flow to decline by 9.3 percent.
Snow falling in smaller amounts, less frequently, and melting earlier impacts not only the water supply, but also the recreation and tourism economy, as Colorado’s ski season gets shorter. One study by researchers at University of Colorado Boulder and the EPA found that Colorado’s number of skiable days will decrease by 33 days by 2050, which will result in millions of lost winter recreation visits.
Human health impacts
The diverse impacts of climate change in Colorado will also affect the health of Coloradans in several ways. Rising temperatures – and extreme heat days in particular – can have devastating impacts on vulnerable populations, such as children, the elderly, people living in poverty, the homeless, and those with certain preexisting conditions. Temperatures above 90 degrees Fahrenheit can be harmful to human health, and it is estimated that Colorado’s average summer temperature could be in the low-to-mid 90s by mid-century. Extreme heat affects cardiovascular, respiratory and nervous systems, and can also cause heat stroke and dehydration. As temperatures warm, this is concerning, because nearly 6 percent of Colorado’s adults have cardiovascular disease, which puts them at an increased risk for heat exhaustion and heat stroke. Approximately 7 percent of Colorado’s adults have diabetes, which means they can have trouble cooling their bodies on hot days, due to damage to the blood vessels and nerves that impact sweat glands. Higher temperatures also impact how a diabetic person processes insulin, requiring more frequent blood sugar tests and careful dietary choices. The 1.2 million children in Colorado and the 711,000 seniors are also particularly vulnerable to the impacts of extreme heat. Children absorb more heat than adults since they have a greater ratio of skin surface to weight, and the elderly are particularly vulnerable because chronic illness, age, and prescription medications can hinder the ability to regulate body temperature.
Poor air quality due to climate change has a multitude of negative effects on human health. Changes in weather patterns due to climate change – including slight changes in humidity, cloud levels, wind, and temperature – can increase pollutants like ozone, carbon dioxide, and particulate matter. High levels of ground-level ozone can be particularly problematic for human health, as ozone is a lung irritant that can cause breathing problems. This puts the approximately 500,000 Coloradans with asthma and the 180,000 Coloradans with respiratory ailments like Chronic Obstructive Pulmonary Disease (COPD) at an increased risk. This is particularly problematic, as the Denver Metro/Northern Front Range area has been in “serious” ozone nonattainment for more than a decade, consistently violating EPA ozone standards.
Additionally, particulate matter and CO2 can cause or exacerbate allergies, and warmer temperatures coupled with more CO2 can promote the growth of plants that release airborne allergens, affecting the allergy season.
Wildfires – and wildfire smoke – have numerous impacts on human health. In addition to the immediate harms of burns, smoke inhalation, traumatic injury, and post-traumatic stress, smoke can travel long distances and have secondary impacts. For instance, induced asthma, chest pain, nose and eye irritation, and coughing can occur. The particulate matter (PM 2.5) found in smoke can increase the risk of lung cancer, cardiovascular disease, asthma and COPD for the 3 million Coloradans living in wildland-urban interface areas.
