Rose Andreatta

Last updated January 6, 2022

Marshall Fire December 2021

United States

An urban firestorm fueled by hurricane-force winds incinerated nearly 1,000 homes and structures in and around Boulder, Colorado in just one day, making it the most destructive wildfire in the state's history. Climate change, primarily caused by the extraction and combustion of fossil fuels, supercharges fires like the Marshall Fire through increased temperatures and exacerbated drought. In all, an estimated 6,000 acres were burned by the fire.

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Hundreds of homes were damaged in the Marshall fire.

Climate science at a glance

Climate signals breakdown

Climate signals #1: Land surface temperature increase

Climate change has significantly increased air and land temperatures in the Western US. These higher temperatures can make droughts worse. Warmer winters also mean less snowpack or earlier snowmelt, while warmer summers further increase and dry out already parched soil and plants. These conditions, along with high winds, can lead to record-breaking wildfires. In some cases, the extreme heat and dryness can cause explosive fires that burn hundreds or thousands of acres in just a few days.

Observations consistent with climate signal #1

  • Temperatures in Colorado between June and December were the warmest on record.
  • Unusually warm conditions intensified drought conditions in Colorado from the summer through the end of the year.

Climate signals #2 & #3: Land surface drying & drought risk increase

Global warming is altering regional water cycles. Warmer air can hold more moisture, which means it takes more water for the air to be fully saturated. When the air is not fully saturated, the difference between the amount of moisture in the air – and how much moisture the air can hold – is known as vapor pressure deficit (VPD). High VPD (which occurs when the air needs much more water to be fully saturated) increases rates of water loss from plants and soils (known as evapotranspiration), and this, in turn, causes drying and heating of land surfaces and contributes to more frequent and severe drought and wildfire events.

Zhuang et al. 2021 find that over two thirds (68%) of the increase in vapor pressure deficit  in the western US between 1979 and 2020 is due to climate change.

Observations consistent with climate signals #2 & #3

Climate signal #4: Season creep

Higher temperatures are extending the fire season in the western US by shifting conditions more characteristic of September and October to November and December.

"I think one thing that’s really important to note [about the Marshall fire] is that this is a winter wildfire...there’s only one other time in my career when I’ve talked about snow putting out wildfires...This is an important signal. And we’ve seen this signal across the West."

Jennifer Balch, director of the Earth Lab at the University of Colorado, Boulder

Observations consistent with climate signal #4

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Rose Andreatta

Rose Andreatta is the director of the Climate Signals project and has over a decade of experience translating scientific information into usable formats for a variety of audiences. Rose earned her Master’s of Public Administration in Environmental Science and Policy at Columbia University and holds a Certificate of Achievement in Weather Forecasting from Pennsylvania State University.