The Science Behind BC's 2017 PyroCb Event
How extreme wildfires created a hemispheric atmospheric phenomenon that rewrote our understanding of fire-weather interactions
In August 2017, something extraordinary happened in the skies over British Columbia. Raging wildfires, fueled by dry conditions and favorable meteorology, did something that only the most powerful volcanic eruptions typically accomplish—they pushed massive amounts of smoke high into the stratosphere, where it would persist for months and spread across the entire Northern Hemisphere. This phenomenon, known as pyrocumulonimbus (pyroCb), represents one of nature's most dramatic displays of fire-weather interaction.
What began as a regional environmental disaster quickly evolved into a global atmospheric event that would captivate scientists for years to come. The 2017 British Columbia pyroCb event provided an unprecedented opportunity to study how extreme wildfires can influence our atmosphere on a hemispheric scale, with implications for climate science, atmospheric physics, and our understanding of increasingly severe wildfire seasons in a warming world.
Pyrocumulonimbus clouds are essentially fire-generated thunderstorms. Unlike ordinary cumulonimbus clouds that form through conventional heat and moisture processes, pyroCb events occur when intense heat from wildfires creates powerful updrafts that carry smoke, ash, and combustion products high into the atmosphere.
What makes pyroCb events particularly significant is their ability to inject smoke directly into the lower stratosphere, approximately 10-15 kilometers above Earth's surface. At these altitudes, above the weather-producing troposphere, aerosols and particles can persist for much longer periods—months instead of days—and travel globally rather than just hundreds of kilometers.
The August 2017 pyroCb event in British Columbia was exceptional in its scale and power. Researchers later estimated it injected between 0.1 to 0.35 teragrams of smoke aerosols into the upper troposphere and lower stratosphere 4 . To put this in perspective, this was comparable to the aerosol output of a moderate volcanic eruption.
While volcanic aerosols primarily scatter sunlight back into space (exerting a cooling effect), wildfire smoke contains absorbing carbon particles that trap heat, potentially warming the surrounding atmosphere while cooling the surface below 4 . This distinction would prove crucial to understanding the event's broader environmental impacts.
Extreme heat creates powerful updrafts
Fire-generated thunderstorm develops
Smoke reaches 10-15 km altitude
Within days of the pyroCb event, scientists worldwide mobilized to track the massive smoke plume using an array of satellite-based instruments:
These coordinated observations revealed something remarkable: the smoke plume wasn't just passively traveling with wind currents—it was actively lifting itself higher through a phenomenon known as "aerosol self-lofting."
The concept of aerosol self-lofting provided the key to understanding the smoke plume's unexpected behavior. Here's how it works:
Dark carbon particles in the smoke, including black carbon and brown carbon, absorb incoming solar radiation.
This absorption heats the surrounding air, making the smoke plume more buoyant than the surrounding atmosphere.
The heated air parcel rises, carrying the smoke particles to higher altitudes.
At higher altitudes, with less dense atmosphere, the heating effect becomes even more pronounced, creating a positive feedback loop.
The British Columbia event provided the first comprehensive dataset to study this phenomenon on such a massive scale. The plume demonstrated an initial ascent rate of 2-3 kilometers per day in the first few days after injection—far faster than conventional atmospheric models predicted 4 .
| Time After Injection | Altitude |
|---|---|
| Initial (August 2017) | ~12 km |
| 3-5 days | ~15-18 km |
| 19 days | ~22 km |
| 2-3 months | 20-23 km |
| 8-10 months | Gradually descending |
To unravel the complexities of the pyroCb event, scientists at NASA's Goddard Space Flight Center employed the Goddard Earth Observing System (GEOS) atmospheric general circulation model 4 . This sophisticated computer simulation allowed researchers to create a virtual laboratory where they could test hypotheses about the smoke plume's behavior under controlled conditions.
The research team faced significant challenges in configuring their model:
The resulting simulation represented a breakthrough in atmospheric modeling, successfully replicating both the immediate self-lofting and the longer-term transport of the smoke plume with remarkable accuracy compared to OMPS-LP observations 4 .
The GEOS model simulations revealed several crucial aspects of the pyroCb event:
The smoke aerosols caused significant warming of the stratosphere, with estimated zonal mean radiative impacts of 0.6-1 W/m² that persisted for 2-3 months in regions north of 40°N latitude 4 .
While the atmosphere warmed, the Earth's surface experienced comparable cooling as less sunlight reached ground level—a phenomenon with potential implications for regional weather patterns.
The model confirmed that both aerosol self-lofting and large-scale atmospheric motion played important roles in sustaining the stratospheric smoke plume for much longer than typical tropospheric smoke events.
| Impact Type | Magnitude | Duration | Location |
|---|---|---|---|
| Atmospheric warming | 0.6-1 W/m² (zonal mean) | 2-3 months | Primarily stratosphere, north of 40°N |
| Shortwave heating rate increase | 0.02-0.04 K/d | September 2017 | Coincident with smoke plumes |
| Surface cooling | Comparable to atmospheric warming | 2-3 months | Regions under smoke plumes |
| Stratospheric residence | e-folding time ~5 months | 8-10 months | Northern Hemisphere stratosphere |
Studying extreme events like the British Columbia pyroCb requires sophisticated technology and methods. Contemporary researchers employ a diverse toolkit:
Vertical profiling of aerosols and clouds for tracking vertical distribution and ascent of smoke plumes
Measuring stratospheric aerosol extinction for monitoring long-term persistence and spread of smoke
Detecting absorbing aerosols for identifying self-lofting behavior in smoke plumes
Simulating physical and dynamical processes for testing hypotheses about transport and radiative impacts
Investigating surface chemical properties for analyzing chemical composition of smoke particles 2
Detecting species via environmental DNA for studying ecological impacts of wildfires 3
The 2017 British Columbia pyroCb event fundamentally changed our understanding of how extreme wildfires can influence Earth's atmosphere.
The discovery that smoke plumes can self-loft into the stratosphere and persist for months while traveling across the hemisphere has rewritten textbooks on atmospheric science.
As climate change increases the frequency and intensity of wildfires globally, the lessons from British Columbia's 2017 event become increasingly vital. These findings suggest that extreme wildfires may have climate impacts far beyond their immediate regions, potentially influencing atmospheric circulation patterns and radiation budgets on hemispheric scales.
The event also demonstrated the power of modern Earth observation systems and atmospheric models to unravel complex environmental phenomena. As one research team noted, the combination of satellite data and sophisticated modeling allowed for unprecedented tracking and analysis of the smoke plume's journey 4 .
What began as a regional disaster in British Columbia has evolved into a case study with global implications, reminding us that in our interconnected Earth system, even regional events can have worldwide consequences—and that scientific curiosity can transform catastrophe into insight.