Fog over Hurricane Ridge, Olympic National Forest — © Shasta Willson 2018

SmokeStorms: a return to normal?

Smoke as thick as the familiar winter fog blankets Seattle this August. Amid the apocalyptic light, arguments blaze: is this the new normal, and if so, what’s driving it?

Perhaps, some argue, it’s not even new.

Compared to the wildfires that blazed across the West a century ago, these fires burn very little acreage. Until 1910, fire swept through our forests every 5–15 years.[1] With their thick bark and stratospheric branches, giant old growth trees survived the flames that swept away underbrush and smaller trees, leaving open understory and a healthy forest.

After the Great Fire of 1910 burned more than 3 million acres, killed 78 firefighters and destroyed most of Wallace, Idaho, the Forest Service began to take fire suppression quite seriously. For decades, fire was contained.

Then it returned.

The total annual area burned has grown from around 2 million acres in 1985, to nearly 8 million acres in 2017[2][3]. These fires are not like the cool, fast, wide-ranging fires that dominated the pre-suppression era. These hotter fires burn everything to the ground. They are often unstoppable.

Humans are adaptable and innovative. We’ve gotten better at fighting fires. We’re investing more money[4]. Despite this, firefighting fatalities are up[5], property destruction is up[6], and total acreage burned keeps increasing. The lay of the land is changing, and we need to know why.

Decades of fire suppression allowed fuel to accumulate[7] in the form of underbrush and debris. Clearcuts and second-growth forests feature smaller trees surrounded by taller brush that can help fire “crown” into even the tallest trees. These conditions create forests that burn to the ground in hot, hard-to-control fires. For forests on the West Coast, there is no question that this contributes to the problem. This is established science that has been incorporated into forest management for decades.

Since the 1970s, we’ve practiced prescribed burns and allowed burns, as well as mechanical clearing, to correct this mistake. Coalitions of environmental[8], Forest Service, and timber industry groups successfully deploy fire in support of forest health, informed by scientific research[9]. Public approval and political will are growing. This is all necessary, but does it explain the growth in area, severity and destructive power of fires since the mid 80s?

In the West, our fire season lasts a month longer[10] than it did a few decades ago. That’s about the weather. Forests that didn’t traditionally burn, or that were not suppressed[11], are also seeing seasons worsen. California had an historically bad fire season in 2017[12] — then beat that record in 2018[13] — and underbrush alone doesn’t explain that.

Take another look at the graph above. Orange bars represent drought years, while the yellow ones are normal years. The correlation between fire severity and drought conditions is clear. Science confirms[14] that drought has been the primary indicator of severe fire seasons since long before Smokey the Bear. The more often we experience high temperatures and low humidity, the more we’ll be scourged by intense fire seasons. We know this, intuitively, scientifically, and because Smokey told us so.

Climate change affects ecosystems in complicated ways. In some parts of the world, increased precipitation means fewer fires. That is not the case on the West Coast[15]. Here, warmer, wetter winters cause rapid growth of tender vegetation, which dries to tinder as earlier springs bring drought and high temperatures. Climate change makes trees more susceptible to pests and disease[16], and even leads to increased lightning strikes[17], but let’s keep it simple: when conditions are drier, fires are fiercer.

“…declines in summer precipitation and wetting rain days have likely been a primary driver of increases in wildfire area burned.”
Holden et. al, PNAS, Aug. 2018 [18]

Intuitively, we know that hotter, drier weather promotes fire. In fact, hot, dry weather doesn’t just make fires more likely. It makes fires worse[19]. And climate change is making the West hotter and drier[20]. Anthropogenic climate change is estimated to have doubled the region burned[21] in the Western states since 1984, due to increased aridity. There is no serious debate about the correlation between aridity and fire.

We demonstrate that human-caused climate change caused over half of the documented increases in fuel aridity since the 1970s and doubled the cumulative forest fire area since 1984.
— Abatzoglou et. al. PNAS Oct 2016 [22]

Dozens of additional studies confirm what we already intuitively knew, yet people argue that the “real” problem is accumulation of fuel, or a lack of funding for fighting fires, or even environmentalists blocking logging. Some of these arguments are self-serving, but many seem sincere. Maybe it’s easier to blame the Forest Service, or bureaucrats, or activists, than to admit that climate change is evident all around us. Despite our reluctance to face facts, research indicates that anthropogenic climate change is a far more significant driver than forest management history.

Here, we show that large wildfire activity increased suddenly and markedly in the mid-1980s…temperature signal alone explains 66% of the variance…
— Westerling et. al. Science Aug 2006 [23]

Rolling back climate change will be hard. The underlying issue of human behavior remains intractable, and the effects of climate change won’t easily be reversed. Lag in the system means that our best-case outlook includes decades of worsening conditions. We don’t even talk about the all-out war on climate change that would be necessary for that best case. The scale of the problem feels overwhelming, and it’s tempting to hope it will work itself out while we busy ourselves with smaller problems.

It won’t.

…projections indicate an impending shift to a temperature-driven global fire regime in the 21st century, creating an unprecedentedly fire-prone environment.
— Pechony et. al. PNAS Oct 2010 [24]

To survive this critical moment in human history, we need to address the immediate issue of forest health, and also the long-term problem of reversing global warming. These issues are not opposed, but complementary. Healthy forests are essential to addressing climate change, just as addressing climate change is essential to healthy forests.

Prescribed burns and scientifically driven culling are likely to be important to this process in some forests. Some of this science will change as the climate changes. The fight will get harder before it gets easier, but we can win it. We can bring the indomitable spirit that took us to the moon and the persistence that ended smallpox to this problem. We are the most adaptable, creative, and hopeful species on this planet, and we can win this battle. We have the science and technology to get started now.

For our grandchildren to enjoy cool, green forests producing clear, breathable summer skies, the first step is to admit that we know the problem.

We need to do that right now.


  1. Washington Prescribed Fire Council
  2. Wildfire Today: Visualizing California fires over the last 18 years
  3. Wildfires In The U.S. Are Getting Bigger (JUL 2018)
  4. Playing with Fire: The Soaring Costs of Western Wildfires (JUL 2014)
  5. A Century of Wildland Firefighter Deaths (JUN 2013)
  6. Wildfire property damage could reach $65 billion in Northern California (OCT 2017)
  7. Suppression of naturally occurring blazes may increase wildfire risk (MAR 2013)
  8. Conservation Northwest: Wildfires and Northwest Forests
  9. International Journal of Wildland Fire
  10. How Bizarre is this year’s Wildfire Season, Really? (SEP-2017)
  11. The Interaction of Fire, Fuels, and Climate across Rocky Mountain Forests. Tania Schoennagel, Thomas T. Veblen, William H. Romme;
    BioScience, Volume 54, Issue 7, 1 July 2004, Pages 661–676,[0661:TIOFFA]2.0.CO;2
  12. The grim scope of 2017’s California wildfire
    season is now clear. The danger’s not over. (JAN 2018)
  13. Why Today’s Wildfires Are Hotter And More Destructive (AUG 2018)
  14. A review of the relationships between drought and forest fire in the United States. Littell, J. S., Peterson, D. L., Riley, K. L., Liu, Y. and Luce, C. H. (2016); Glob Change Biol, 22: 2353–2369. doi:10.1111/gcb.13275
  15. NASA: Longer, More Frequent Fire Seasons
  16. Why Bark Beetles are Chewing Through U.S. Forests (JAN 2013)
  17. Lightning is Sparking More Boreal Forest Fires in Far North America (NOV 2017)
  18. Decreasing fire season precipitation increased recent western US forest wildfire activity. Zachary A. Holden, Alan Swanson, Charles H. Luce, W. Matt Jolly, Marco Maneta, Jared W. Oyler, Dyer A. Warren, Russell Parsons, David Affleck; PNAS Aug 2018 201802316; DOI:10.1073/pnas.1802316115
  19. Highly episodic fire and erosion regime over the past 2,000 y in the Siskiyou Mountains, Oregon. Daniele Colombaroli, Daniel G. Gavin; PNAS Nov 2010, 107 (44) 18909–18914; DOI:10.1073/pnas.1007692107
  20. Global Warming in the Western United States
  21. Climate Change Has Doubled Western U.S. Forest Fires, Says Study (OCT 2016)
  22. Impact of anthropogenic climate change on wildfire across western US forests. John T. Abatzoglou, A. Park Williams; PNAS Oct 2016, 113 (42) 11770–11775; DOI:10.1073/pnas.1607171113
  23. Warming and Earlier Spring Increase Western U.S. Forest Wildfire Activity. A. L. Westerling, H.G. Hidalgo, D.R. Cayan, T.W. Swetnam; Science AUG 2006 : 940–943
  24. Driving forces of global wildfires over the past millennium and the forthcoming century. O. Pechony, D. T. Shindell; PNAS Oct 2010, DOI: 10.1073/pnas.1003669107

Additional Resources

  1. California Wildfire Season Is Stretching Year-Round (MAY 2014)
  2. Penn State’s Alan Taylor uses model to help predict the unintended consequences of suppressing wildfires.
  3. Global Warming-Fueled Wildfires Increasing, Scientists Say (MAY 2016)
  4. Controlled Burn;
  5. More heat, drought and longer fire season in Canada’s future, experts say (AUG 2018)