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TOPSHOT – This photograph shows smoke rising in the sky in Correns, southeastern France on July 31, 2026, as the fire restarted today in the Var, picking up ‘in scale’ fuelled by the mistral. New evacuations were decided by the authorities” notably in neighborhoods of the communes of Correns and Montfort-sur-Agens, indicated the prefect of the Var, Simon Babre and “2,000 have been evacuated”, in total.
\nThibaud MORITZ\/gettyimages.com<\/p>\n
When Europe’s most destructive wildfire in decades tore through France’s Gironde region last month, its smoke did not simply drift south toward the sea. It climbed \u2014 carried by the violent updrafts of a pyrocumulonimbus, or “fire thunderstorm,” that scientists had never before recorded over France \u2014 all the way to the boundary of the stratosphere, roughly 11 kilometers (36,000 feet) above the ground. German atmospheric scientists confirmed on Wednesday that smoke from the Bordeaux fire reached that altitude above Leipzig, more than 1,000 kilometers (621 miles) from the fire zone, making it the first European-origin wildfire smoke plume to be detected at near-tropopause height by instruments at the Leibniz Institute for Tropospheric Research<\/a> (TROPOS).<\/p>\n That threshold matters. Below roughly 10 kilometers (33,000 feet), wildfire smoke stays in the troposphere, where rain washes particles out within days and the climate impact remains largely regional. Once smoke crosses the tropopause into the stratosphere, the dynamics reverse: no precipitation, no rapid removal. Particles can persist for months, spreading across an entire hemisphere on upper-level winds. The Bordeaux measurements, confirmed by TROPOS’s flagship MARTHA lidar system, suggest that Europe’s escalating fires have crossed a new climate threshold<\/a> previously associated only with catastrophic North American megafires and moderate volcanic eruptions \u2014 one with consequences that extend well beyond the region that burned.<\/p>\n What TROPOS Found \u2014 and How<\/p>\n The MARTHA system \u2014 an acronym for Multiwavelength Atmospheric Raman Lidar for Temperature, Humidity, and Aerosol Profiling \u2014 fires laser pulses into the sky above Leipzig at three wavelengths (355, 532, and 1,064 nanometers) and analyzes the backscattered light through a primary mirror 80 centimeters<\/a> (31.5 inches) in diameter.<\/p>\n What makes the current detection possible is an upgrade that TROPOS completed in August 2022: a fluorescence detection channel added to the MARTHA system, further enhanced at the end of 2023 with a more powerful laser and a 32-channel spectrometer. The upgrade uses a key physical property of wildfire smoke that volcanic ash and mineral dust do not share: organic compounds in smoke particles fluoresce when struck by laser light, emitting a broadband optical signal that allows TROPOS researchers to distinguish fire smoke from other aerosol sources unambiguously \u2014 even at altitudes where the two types of particle might otherwise be indistinguishable. In 2021, researchers at TROPOS documented how an earlier-generation system had misclassified Siberian smoke as volcanic aerosol<\/a> over Leipzig, precisely because it lacked this fluorescence capability.<\/p>\n During the nights of July 28 through 30, 2026, the MARTHA fluorescence channel detected two distinct smoke layers over Leipzig: one concentrated between 3 and 7 kilometers (10,000 to 23,000 feet), and a second, thinner layer at 10 to 11 kilometers (33,000 to 36,000 feet) \u2014 that second layer sitting directly at the tropopause.<\/p>\n “The temporal evolution of the measured fluorescence backscatter identifies layers of smoke at altitudes of 3 to 7 and 10 to 11 kilometres,” reported Benedikt Gast, a TROPOS doctoral researcher whose dissertation focuses on long-range wildfire smoke transport using fluorescence lidar. He noted that in the past, smoke layers at such heights<\/a> had only been observed over Leipzig from fires in North America.<\/p>\n How Researchers Traced the Smoke Back to Bordeaux<\/p>\n Detecting a smoke layer is one thing. Knowing where it came from requires a separate analytical step: backward trajectory modeling, which reconstructs where air masses were located in the hours and days before they arrived over a measurement site. The TROPOS team ran backward trajectories for the air masses in which the high-altitude smoke layers were detected.<\/p>\n The results were unambiguous. Air masses at 10 to 11 kilometers altitude over Leipzig had been directly over the wildfire zone near Bordeaux approximately 15 hours before the lidar detected them. Twenty-four hours before that, those same air masses had been over active fire zones in central Spain. “It therefore stands to reason that the smoke particles measured by the lidar originate from these fires in France and\/or Spain,” Gast said.<\/p>\n Whether the near-tropopause smoke injection was driven specifically by the identified pyrocumulonimbus event, or by conventionally triggered deep convection within the same frontal weather system, remains scientifically open. A convective cloud near the Bordeaux fire zone was observed on the afternoon of July 25 and assessed as meeting the criteria for pyroCb classification, which would be at minimum an extremely rare event for central Europe. But Jason M\u00fcller, a TROPOS doctoral researcher who models pyroCb formation, noted that the cloud formed in the context of a synoptic-scale frontal system \u2014 meaning that conventionally driven thunderstorms also occurred nearby, which are themselves capable of transporting smoke to high altitudes.<\/p>\n “The extent to which the smoke measured over Leipzig can be attributed to a single pyrocumulonimbus event remains to be clarified,” M\u00fcller said. The distinction matters for quantifying exactly how much of the smoke injection was driven by the fire’s own convective engine versus the surrounding weather \u2014 but it does not affect the core finding that the high-altitude smoke arrived from the Bordeaux fire zone.<\/p>\n Why the Altitude Makes This a Climate Story, Not Only a Fire Story<\/p>\n The altitude at which smoke enters the atmosphere determines how long it stays there and how far it travels \u2014 and, by extension, how much it matters to the global climate. Smoke that stays below the tropopause gets washed out by rain within days. Smoke that crosses into the stratosphere enters a different regime: it circulates on global wind patterns and can influence Earth’s energy balance for months.<\/p>\n A 2023 study in the journal Science, led by atmospheric scientist J. M. Katich and a research team that included scientists from NOAA and CIRES, analyzed 13 years of airborne observations and found that pyrocumulonimbus events are responsible for 10 to 25 percent of the black carbon in lower stratosphere<\/a> and of organic aerosols currently present there \u2014 with comparable contributions in both the Northern and Southern Hemispheres. That study found that pyroCb events, once considered rare and episodic, exert what the authors described as a “steady state influence” on the stratosphere that global climate models have not fully accounted for.<\/p>\n The Bordeaux observations extend that picture to Europe. “In the past, smoke layers at such altitudes have only been observed over Leipzig from very severe forest fires in North America,” Gast noted. “This fact underlines the large scale of the fires by European standards and suggests that high-altitude pyroconvection occurred.”<\/p>\n How Fire Smoke Becomes a Climate Force<\/p>\n The climate physics of high-altitude wildfire smoke is complex and still not fully resolved. Particles injected into the upper troposphere and lower stratosphere produce several distinct effects that can compound warming, cool the surface, or alter cloud formation \u2014 sometimes simultaneously.<\/p>\n Soot particles \u2014 black carbon \u2014 absorb incoming solar radiation, warming the surrounding atmospheric layers. This warming occurs in addition to the warming effect already produced by the greenhouse gas emissions from the fires themselves, meaning that large pyroCb events function as an aerosol-driven accelerant to global warming, not merely a symptom of it. At the same time, the same soot particles can seed the formation of high, thin ice clouds \u2014 known as cirrus \u2014 which reduce solar radiation reaching the ground while trapping outgoing longwave radiation from Earth’s surface, producing a separate warming contribution.<\/p>\n “Depending on their composition, chemical ageing, and their interaction with clouds, the particles can either weaken or amplify incoming solar radiation,” said Prof. Ina Tegen, who leads TROPOS’s atmospheric process modeling department and serves as the spokesperson for the Leibniz Science Campus “Smoke and Bioaerosols in a Changing Climate” (LSC BioSmoke). “These relationships have not yet been sufficiently researched, but they pose major challenges for climate research \u2014 particularly in view of the increasingly severe forest fires expected in a warming climate.”<\/p>\n Dr. Bernd Heinold, who leads TROPOS’s aerosol-radiation-climate research team and has modeled pyroCb events in Australia using atmospheric models, added that the extreme wildfires involving pyrocumulonimbus clouds pose specific new challenges for aerosol-climate science: they transport smoke particles and trace gases into the upper troposphere and lower stratosphere “where they can influence radiative processes and the formation of ice clouds. These processes are not yet fully understood and have so far only been represented to a limited extent in global aerosol-climate models.”<\/p>\n Europe’s First Pyrocumulonimbus on Record<\/p>\n On July 26, France’s National Firefighters Federation (FNSPF) confirmed that the Gironde wildfire had produced a pyrocumulonimbus \u2014 the first such event officially recorded in France \u2014 in a statement relayed by AFP<\/a>. A pyrocumulonimbus forms when a wildfire releases enough heat to drive a rising column of hot air, smoke, and moisture that becomes unstable enough to develop into a full cumulonimbus thunderstorm \u2014 complete with its own violent wind gusts, lightning strikes that can ignite new fires far from the original front, and virga (rain that evaporates before reaching the ground in the hot, dry air below).<\/p>\n French wildfire researcher Jean-Baptiste Filippi described the phenomenon in a France 24 interview on pyroCb<\/a> as particularly challenging for firefighters: fire clouds generate their own unpredictable wind patterns, making the fire’s behavior far harder to anticipate.<\/p>\n The Gironde wildfire, which ignited July 22 near the Atlantic coast, grew to more than 42,000 hectares (approximately 104,000 acres) \u2014 the largest single wildfire in France since the 1949 Landes fire \u2014 and forced the evacuation of more than 220,000 people<\/a> from the Gironde and Landes departments. By late July, Interior Minister Laurent Nu\u00f1ez told France 24 that France was simultaneously battling 30 to 40 wildfires<\/a> daily, with 115,000 hectares burned nationally. The Gironde fire burned an area approximately four times the size of Paris before it was declared stabilized on July 28 \u2014 though not extinguished.<\/p>\n What Happens to the Smoke Now<\/p>\n Once injected near or above the tropopause, wildfire smoke aerosols do not simply disperse. They undergo what atmospheric chemists describe as “aging” \u2014 a sustained series of chemical reactions and physical processes that alter their optical properties, their toxicity, and their interactions with clouds. How this aging changes the particles’ climate and health impacts is, in the words of Dr. Yar\u00ea Baker, a TROPOS atmospheric chemist working within the LSC BioSmoke collaboration, “a highly topical area of research, in which many questions remain unanswered.”<\/p>\n A broader scientific dossier on wildfire aerosols \u2014 covering their spread, climate effects, and health impacts \u2014 was published by the Science Media Center Germany<\/a> on July 31, 2026, with five TROPOS and LSC BioSmoke researchers among the contributors.<\/p>\n