Rocky Mountain Forests Burning More Now Than Any Time in the Past 2,000 Years

By Philip Higuera, Professor of Fire Ecology and Paleoecology, The University of Montana, Bryan Shuman, Professor of Paleoclimatology and Paleoecology, University of Wyoming. and Kyra Wolf, Ph.D. Student in Systems Ecology, The University of Montana. Originally published at The Conversation.

The exceptional drought in the U.S. West has people across the region on edge after the record-setting fires of 2020. Last year, Colorado alone saw its three largest fires in recorded state history, one burning late in October and crossing the barren Continental Divide well above the tree line.

Those fires didn’t just feel extreme. Evidence now shows the 2020 fire season pushed these ecosystems to levels of burning unprecedented for at least 2,000 years.

That evidence, which we describe in a study published June 14, 2021, serves as a sobering example of how climate change is altering the ecosystems on which lives and economies depend. A previous study nearly a decade ago warned that by the mid-21st century, climate warming could increase burning past historical levels and transform some Rocky Mountain forests. Our results show such changes in fire activity are now underway.

Historically, fires burned in the subalpine central Rockies every 230 years, on average. That has increased significantly in the 21st century. Philip Higher

Entering Uncharted Territory

As paleoecologists – scientists who study how and why ecosystems changed in the past – we’ve spent decades researching how wildfires, climate and forests change over time.

We used to be able to look to the past when rare events like large wildfires occurred and say “we’ve seen this before and our ecosystems have generally bounced back.” In the last few years, however, it’s become increasingly clear that many ecosystems are entering uncharted territory.

Witnessing the exceptionally large fires burning in high-elevation forests in 2020, unusually late in the season, we wondered if we were experiencing something truly unprecedented.

In Colorado and Wyoming, the largest fires of 2020 were burning in a region where our research teams have spent over 15 years developing records of fire history and ecosystem change from materials preserved in the bottom of lakes. This work has centered on understanding how climate change might one day affect wildfires. We looked to those records for an answer.

Evidence of Past Fires Preserved in Lake Sediments

When a fire burns a forest, it sends tiny bits of charcoal into the air. If a lake is nearby, some of that charcoal will settle to the bottom, adding to the layers that build up each year. By plunging a long tube into the mud and extracting a core, we can examine the history of the surrounding landscape – revealed in the layers of everything that sank to the bottom over thousands of years.

Carbon dating of tree needles and twigs helps us determine the age of each layer in a core. Pollen preserved in the sediments can tell us what grew nearby. And dense charcoal layers tell us when fires burned.

We used such records of past fires preserved in the sediments of 20 lakes in the central Rocky Mountains. In total, the dozens of researchers who helped analyze these cores counted over 100,000 tiny charcoal pieces, within the thousands of 0.5-centimeter layers of lake sediments examined. Identifying distinct increases in charcoal accumulation within the cores allows us to estimate when fires burned around a lake, and compare today’s patterns to those of the distant past.

The result: The extensive burning over the 21st century is unprecedented in this region in the past 2,000 years.

Burning Nearly Twice as Often as in the Past

We estimated that fires burned the forests around each lake once every 230 years, on average, over the past 2,000 years. Over just the 21st century, the rate of burning has nearly doubled, with a fire now expected to burn a given spot once every 117 years.

Even more surprising, fires in the 21st century are now burning 22% more often than the highest rate of burning reached in the previous 2,000 years.

That previous record was established around 1,100 years ago, during what’s known as the Medieval Climate Anomaly. The Northern Hemisphere at that time was 0.3 C (0.5 F) warmer then than the 20th century average. Subalpine forests in the central Rockies during the early Medieval Climate Anomaly burned on average once every 150 years. To put that period’s temperature into perspective, the Northern Hemisphere in 2020 was 1.28 C (2.3 F) above the 20th century average.

In an earlier study based on a subset of the same records, the Medieval Climate Anomaly stood out as a harbinger of what could happen as Rocky Mountain forests warmed. Research in the boreal forest of central Alaska has also documented unprecedented burning in recent decades.

Climate Change is the Culprit, with Accomplices

Research clearly links recent increases in fire activity across the West to increasingly warm, dry summers and human-caused climate change. Our evidence shows that the rate of burning over the past 2,000 years also tracked smaller variations in the climate in the central Rockies.

Warmer, drier conditions make vegetation more flammable, loading the dice for the possibility of large fires. Human activities, a history of suppressing most fires and insect-killed trees all affect when, where and how fires burn. These influences vary across the West and each is layered on top of the warmer, drier conditions of the 21st century.

Adapting to a future unlike the past will be a significant challenge for land managers, policy makers and communities. Reducing the threats of increasing wildfires requires both combating climate change and learning to live in ways that help make our communities more resilient to our fire-prone future.

Print Friendly, PDF & Email


  1. Tom Stone

    The Russian River is lower than I have ever seen it and it has just been announced that flows for Lake Sonoma will be cut in half.
    We are going to see a record fish kill on the lower river.
    If you live in the US Southwest or west it would be a good idea to pick up air filters for your vehicles. you r air purifier and extra N95 masks for your self while they are available.

  2. miningcityguy

    I live in Montana in the Rocky Mountains in a high mountain valley on the west slope of the Continental Divide. The weather here has been extremely hot with strong winds in the afternoon. This is unusual for June which has typically been a more rainy month with baseball games and softball games being frequently rained out. Just about everybody I talk to is concerned about the possibility of major forest fires this year.

    1. Krystyn Podgajski

      I just drove through Southern Wyoming and stayed at a campground on the Green River south of the fontenelle reservoir. I met a old timer and he said they shut down flow from the upstream dam and the river was never lower.

      I checked this site today and boy he was right. Way off the median discharge rate:

      There is a great Twitter feed for fire watchers:

      1. Alex Cox

        They also have a website —

        Today the main stories are the fire south of Red Bluff in Montana, and the plight of federal wildland firefighters, who are quitting in droves — their current pay rate is $13.45 an hour.

  3. PlutoniumKun

    Even the wet parts of Europe have suffered. Ireland has had the four driest springs on record over the past five years. In each case it was an unusually period of 4-6 weeks with no rain in between the usual rain, hail, sunshine and showers that we call a climate.

    Its particularly damaging as it seems to hit before the sap rises and dead winter vegetation is still on the ground, so upland moors and forests are very vulnerable to fire. There was enormous damage last April before the rain returned.

    Thankfully though, a wet and mild May meant very strong growth. The upland peat bogs look in good condition (i.e. wet and deep purple and green, as they should be this time of year), and the long grass in my local park is particularly magnificent this month – my evening stroll last night was enlivened by dozens of swifts swooping around me to catch the clouds of insects.

  4. vw

    For those readers who are under 60 and live in the Southwestern United States – I’d say roughly from the lower half of California east to Oklahoma, and from west Texas as far north as Wyoming – I want to wave a tiny flag in the comments section and humbly ask DO YOU HAVE AN ESCAPE PLAN?

    Frankly, I can’t see large-scale human civilization (especially of a ‘traditional’ suburban type) being possible throughout that region by the end of the century. And the outcome of that will be… well… you can imagine, can’t you?!

    I know contemplating this is terrifying – I live in a region which will likely be overwhelmed by refugee flows from this area when the inevitable really kicks off, a situation plenty terrifying even from the ‘other side’ – but the consequences of not having a plan could be even worse, no? And perhaps leaving before all the rush – might not be such a bad thing, no?

    If this comment pushes even one person further towards creating the plan B that all of y’all are going to NEED… it will have been worth the effort to type.

    1. Wukchumni

      We have the steepest drop of all rivers in the country, the mighty Kaweah never fails in garnering the goods from every last creek, outlet stream, springs & rivers in the backcountry.

      I’m emulating the Native Americans, who largely avoided what are now the big cities in Cali, by living as close to the water as possible…

      There are a few dozen other people who get their water coming down from on high before me straight from the source, so maybe i’m #39 in line for the liquid largess, not 39,452,261st in line.

      I wouldn’t trade my property for a beachfront pad in Malibu, that has all the water you could ever want, and not a drop fit to drink.

      Equity refugees from here have really skewed real estate markets wherever they’ve gone, and the newer drought caused arrivals will be dead broke instead, pauperazzi. You get the feeling we’re going to be loathed on both ends…

      Nobody’s going to bag on you for being a Californian, if you stay here.

      1. vw

        So long as you’ve got a plan and have some idea of what’s coming down the pipe – that’s all any of us can realistically do. I’d guess NC readers are a bit more likely to have their finger on the pulse of precipitating events than the general population.

        You’re correct that as time goes by, refugees are going to be increasingly less likely to be welcomed wherever they end up.

      2. vw

        Also to tag the obvious on at the end for any readers – Malibu is NOT the place to escape to, that whole region’s going to the bottom of the sea around the same timeframe.

        My best guess is that the PNW, Great Lakes area, and the Maritimes are the places you’d want to be for the best long-term prospects, but if anyone has a counter-argument it might be helpful to all to hear it…

        1. lordkoos

          It depends where in the PNW you are talking about. People tend to think of the PNW as Portland & Seattle but once you go east of the mountains it’s a semi-arid climate that is becoming drier every year, but it is still considered the Pacific Northwest region. The coastal areas are a whole different climate than inland, which is drought-stricken. Although even the west side of the Cascades is seeing less rainfall than 20 years ago.

          Here in central WA so far this year we’ve had some decent rainfall, and hopefully this summer will not see so many wildfires. From the map we are technically in “severe” drought but we’ve had more rain this spring than in the last several years.

  5. Wukchumni

    There’s a couple of F-35’s overhead going through their paces, and wasting money that could be spent on squadrons of firefighting planes and helos. It isn’t as if any of our adversaries since the early part of Iraq War #2 even have air forces…

    A CH-47 Chinook was used last year around these parts, and carries a shit-ton of water and/or retardant, and sounded like a freight train when flying over us ferrying to the fire. I see that LA got a couple of these that can fly @ night, recently.

  6. Sound of the Suburbs

    Climate change.
    Don’t worry; a market based solution should be here soon.

    A few decades later …
    Maybe we better get Governments to do it.
    We had to give up on a private sector solution as they were getting nowhere.

    A new ideology swept across the West where the private sector was the answer to all our problems.
    The role of Government was to aid the private sector, and our elected representatives should follow direction from lobbyists to look after the interests of the private sector.

    Government’s role was diminished; the markets and the private sector would provide the solutions to our problems.
    We starved Governments of tax revenue as there wasn’t much for them to do anymore.
    Public service was no longer an attractive proposition to anyone with any real drive and ambition, or vision for a better future. The mediocre could use public service as a stepping stone to a well paid job in the private sector for services rendered during their time in office.

    Thomas Frank has actually investigated the deliberate sabotage of the US Government by the Republicans in “The Wrecking Crew”. The worse the Government is, the quicker the electorate will accept moving things over to the private sector.
    One of the Republican initiatives was to ensure that pay was low in the public sector, so they wouldn’t be able to attract good people. Without good people the Government wouldn’t be able to do a good job and this would make the Government look incompetent, which was the aim.

    Forty years later and they needed the US Government to deal with the coronavirus, but they were not up to the job.
    Most Western governments are in a pretty bad way, and now we need them to deal with climate change.
    I can’t see it going well.

    We need politicians again, but there is a price to pay for the last four decades.


Comments are closed.