42 Scientific American, March 2020
Forest conditions also play a significant role in worsening fires.
After 100 years of aggressive suppression of fires that were essen-
tial for Western ecosystems, the density in many forests now
exceeds their historic norms. For example, in some parts of Cali-
fornia’s Sierras there are 1,000 trees per acre where there were
once be tween 50 and 70. Meanwhile humans keep moving into
fire-adapted biomes. In the 1990s 30.8 million people in the U.S.
lived next to or on lands that regularly burned; 43.4 million do
two decades later. The deadly convergence of these trends was on
full display in 2018’s Camp Fire, a blaze that razed the 26,800-per-
son town of Paradise, Calif., burning 18,804 buildings and killing
at least 85 people, most before the sun had fully risen.
About 4 percent of the entire globe burns every year, and
increasing destructiveness is hardly an American problem alone.
At the time of this writing, Australian bushfires that broke out at
the end of 2019 had burned more than twice the area of Califor-
nia’s 2018 fires and the Amazon’s 2019 fires combined. Although
the total acreage that burns annually is shrinking as natural plac-
es are converted into ranches and cropland, climate change is
now fostering blazes in environments that have no historical
record of raging burns while intensifying fires in places that do.
In the summer of 2018 Northern Ireland saw unprecedented big
fires. So did 7.4 million acres in Arctic and sub-Arctic Siberia.
Fire scientist Stephen Pyne, a professor emeritus at Arizona
State University, has dubbed this era the Pyrocene.
Noaa scientists did not come to wildfire smoke directly; ignor-
ing it just became impossible. In the early 2000s, while studying
haze transported to the Alaskan Arctic via Asia, as well as air
quality outside of Northeastern cities, they were surprised to see
the chemical footprints of wildfires stamped all over their data.
“We’d been focused on urban pollution over the years, but we’d fly
through these urban areas and see all this stuff from wildfires,”
Roberts says. He grew convinced that smoke and air quality
deserved the full weight of Noaa’s research focus. Then, as now,
observational forecasts of fire emissions were unreliable. In a
2008 article in the Journal of Applied Remote Sensing, a compari-
son of four fire-emissions models found that estimates of month-
ly contributions to atmospheric carbon could be off by a factor of- One problem was that North American fire-emissions models
were based on data collected from just 39 different fire events—
a paucity of data considering the variability in fires.
Their interest piqued, Roberts and Warneke, research partners
at Noaa, called their long-time collaborator Bob Yokelson of the
University of Montana, who has been studying wildfire smoke for
almost 30 years. A rangy former firefighter from Montana, Yokel-
son helped lead the initial version of FIREX-AQ. Up until 20 years
ago, he says, field research on wild fire smoke was done only by
him and a few other college professors who rented a Twin Otter,
loaded it with instruments and tooled around the edges of smoke
columns. They were interested in the same aerosols, particulate
matter and gases getting attention from FIREX-AQ, but their
measurements were far coarser. Yokelson was exaggerating the
field’s simplicity, but the assets needed to run a comprehensive
project had never been deployed. It was simply way too expensive
and risky. “We were flying blind into the future,” Yokelson said.
After a string of historically severe smoke seasons clarified that
1© 2020 Scientific American © 2020 Scientific American