Measurements trace European wildfire smoke high into upper troposphere
The images of the major forest fires in Spain and France, with fire clouds near Bordeaux, have shocked many people. There have been numerous reports of the formation of a pyrocumulonimbus cloud—a fire-driven ...
The images of the major forest fires in Spain and France, with fire clouds near Bordeaux, have shocked many people. There have been numerous reports of the formation of a pyrocumulonimbus cloud—a fire-driven thundercloud—and the possible transport of smoke particles to Central Europe.
Researchers at the Leibniz Institute for Tropospheric Research (TROPOS) have now demonstrated that smoke particles from the severe forest fires in southern Europe were indeed transported to Germany at various altitudes.
During the nights from Tuesday to Thursday (July 28–30, 2026), they observed smoke layers over Leipzig at an altitude of 10–11 kilometers (6–7 miles) from midnight onward—an unusually high altitude for European fires. The origin of the air masses could be traced using backward trajectories: The air masses over Leipzig had been over the fire area near Bordeaux about 15 hours earlier.
For the researchers, the lidar measurements provide strong evidence that the forest fires near Bordeaux did indeed result in high-reaching pyroconvection and the transport of smoke particles as far as the upper troposphere.
Up-to-date background information on the topic of "Forest fire aerosols in Europe: dispersion, climate and health" is also provided in a dossier by the Science Media Center Germany (SMC), to which five researchers from TROPOS and the Leibniz Science Campus "Smoke and Bioaerosols in a Changing Climate" (LSC BioSmoke) have contributed.
Aerosol particles influence Earth's energy balance and water cycle: They scatter and absorb incoming solar radiation, thereby affecting the global energy balance. By acting as cloud condensation nuclei or ice nuclei, these particles can influence the microphysical properties of clouds, making them appear more or less bright. Whether cloud droplets remain liquid or freeze also alters the climate impact of that cloud.
That is why researchers from Leipzig at TROPOS, Leipzig University and DBFZ are collaborating within the Leibniz Science Campus "BioSmoke" to investigate the influence of smoke particles on the climate. Their work involves, among other things, atmospheric modeling, laboratory experiments and measurements using laser equipment (lidar).
For many years, the remote-sensing experts at TROPOS have been studying the atmosphere from the ground. To do this, they use a lidar system that emits laser pulses from the ground into the atmosphere above and analyzes the reflected light.
Since 2022, it has been possible to use fluorescence measurements to distinguish biogenic smoke particles originating from wildfires from atmospheric particles originating from other sources, such as volcanoes. In recent years, they have already been able to identify smoke from major wildfires in Canada over Leipzig.
The latest measurements now show a similar picture: "The temporal evolution of the measured fluorescence backscatter identifies layers of smoke at altitudes of 3–7 kilometers (2–4 miles) and 10–11 kilometers (6–7 miles). Backward trajectories for the start time of July 28 at 11 p.m. CEST over Leipzig show that the air masses in which these smoke layers were detected had been over the forest fire area near Bordeaux approximately 15 hours earlier and near fires in central Spain approximately 24 hours earlier.
"It therefore stands to reason that the smoke particles measured by the lidar originate from these fires in France and/or Spain," reports Benedikt Gast from TROPOS, who is investigating the atmospheric transport of wildfire smoke using fluorescence lidar as part of his Ph.D. project.
What is unusual about the current measurements is the high altitude of the smoke layers—at 10–11 kilometers (6–7 miles), close to the tropopause. In the past, smoke layers at such altitudes have been observed over Leipzig only from very severe forest fires in North America. This fact underlines the large-scale nature of the fires by European standards and suggests that high-altitude pyroconvection occurred.
"However, the extent to which the smoke measured over Leipzig can be attributed to a single pyrocumulonimbus event remains to be clarified. During the forest fires near Bordeaux, a convective cloud was indeed observed on the afternoon of July 25 that could certainly be classified as a PyroCb—an event that is, at the very least, extremely rare in Central Europe," explains Jason Müller from TROPOS, who is modeling the formation of PyroCb events in his Ph.D. work.
"However, it formed in the context of a synoptic-scale front, meaning that conventionally triggered deep convection also occurred in the immediate vicinity of the PyroCb. This, too, makes vertical smoke transport possible, for example."
For smoke to rise to high altitudes, even into the stratosphere, and be widely dispersed there, either long periods are required during which the smoke is heated by the sun and rises slowly, or fire-induced thunderclouds transport the smoke rapidly upward, as if in an elevator. Smaller fires do not exhibit these dynamics: Their smoke does not reach such heights and is therefore often quickly washed out by rain in the lower layers of the atmosphere.
As with volcanic eruptions, altitude is also crucial in the case of wildfires: If the particles and gases reach only altitudes below 10 kilometers (6 miles) (the troposphere), the effects on the affected region may be devastating, but their impact on the global climate is limited.
If, on the other hand, the particles and gases reach altitudes above 10 kilometers (6 miles), they can remain in the stratosphere for a long time and are carried by upper-level winds far across the respective hemisphere.
"Depending on their composition, chemical aging and interaction with clouds, the particles can either weaken or amplify incoming solar radiation. These relationships have not yet been sufficiently researched, but they pose major challenges for climate research. They are of particular significance in view of the increasingly severe forest fires expected in a warming climate," summarizes Ina Tegen from TROPOS and the University of Leipzig. She is also the spokesperson for the Leibniz Science Campus "Smoke and Bioaerosols in a Changing Climate" (LSC BioSmoke).
"Extreme wildfires involving pyrocumulonimbus clouds pose new challenges, particularly for aerosol-climate research. They can transport smoke particles and trace gases as far as the upper troposphere or 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 been represented only to a limited extent in global aerosol-climate models," Dr. Bernd Heinold from TROPOS, who has studied these pyrocumulonimbus clouds in Australia using atmospheric models, told the SMC.
"Another important aspect is how wildfire aerosols change after they are emitted. This is because, in addition to transport, a multitude of chemical reactions and physical processes take place in our atmosphere—the emissions 'age," so to speak. How this affects their toxicity and their impact on weather and climate is a highly topical area of research in which many questions remain unanswered and which we at TROPOS are investigating as part of the LSC BioSmoke," Dr. Yarê Baker from TROPOS emphasized to the SMC.
"Forest fire aerosols have a wide range of effects on weather and climate. Smoke particles scatter and absorb incoming solar radiation, which, depending on the thickness of the smoke layer, can reduce the temperature at the ground by several degrees. Furthermore, soot particles act as so-called cloud nuclei and can promote the formation of high, thin ice clouds," reports Dr. Robert Wagner, coordinator of the LSC BioSmoke.
"These clouds further reduce solar radiation at ground level; however, they also trap longwave radiation from Earth and are thought to have a warming effect on the climate. At the same time, the soot produced during combustion warms the atmosphere by absorbing solar radiation. This warming is in addition to the warming effect of greenhouse gas emissions from the fires. Consequently, in the long term, emissions from forest fires are more likely to be associated with a further increase in global warming."
Even though the total quantities of smoke particles are relatively low, in the otherwise fairly clean upper troposphere, at an altitude of around 10 kilometers (6 miles), they can influence the climate in various ways: On the one hand, soot particles reflect part of the incoming sunlight; on the other hand, they also absorb some of it, thereby heating themselves and the surrounding atmospheric layers.
They also promote the formation of high-level ice clouds, which tend to have a warming effect on the climate. Atmospheric researchers are therefore discussing the extent to which forest fires are now influencing the global climate and whether smoke from forest fires could be a factor accelerating global warming.
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Citation: Measurements trace European wildfire smoke high into upper troposphere (2026, August 6) retrieved 6 August 2026 from https://phys.org/news/2026-08-european-wildfire-high-upper-troposphere.html
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