An alarming trend of wildfires in the western US lofting smoke higher in the atmosphere is set to worsen. As fires grow larger with climate change, they are more likely to produce towering storm clouds that can send smoke all the way to the stratosphere.
鈥淭hese really large wildfire-plume rise heights are the ones that are burning the most area and probably producing the most smoke,鈥� says at the University of Utah, who presented the research at the American Geophysical Union (AGU) meeting in Washington DC on 12 December.
When a wildfire grows big and hot enough, it can generate its own weather. Really large fires can form dramatic pyrocumulonimbus clouds that cause high winds and lightning strikes, which spread the fires faster. Some of these clouds carry smoke particles all the way to the stratosphere, delivering roughly as many aerosols as small volcanic eruptions do. There, the pollutants can eat away at the ozone layer, and they may affect the global climate in complex ways by forming ice clouds or heating the stratosphere itself.
Advertisement
Previously, Mallia and his colleagues wildfire plumes across the western US have increased in height since 2003, including a small increase in the number of the largest plumes, which are formed by pyrocumulonimbus clouds. Now, the researchers have modelled how these plume heights will change from now to 2060 under different emissions scenarios, as warming temperatures increase the area burned by fires.
They found a 20 to 30 per cent rise in average plume heights across the region. The tallest plumes saw the fastest rise, doubling in height under a low-emissions scenario and quadrupling with very high emissions.
They didn鈥檛 model plumes further into the future because projections of wildfire size become more uncertain after 2060 due to feedback between fire size and the amount of vegetation left to burn.
The projections also don鈥檛 account for some important details, such as how climate change will shift fuel available for fires as well as change the structure of the atmosphere. 鈥淏ut it does seem like climate change will result in an increase in plume rises based on this very preliminary analysis,鈥� says Mallia.
However, it remains uncertain what impact these huge smoke plumes will have on the climate itself, says at Sorbonne University in France. For instance, black carbon in smoke could lead to warming in the stratosphere 鈥� even as it by blocking sunlight.
It is also unclear how often these clouds can loft smoke to the stratosphere. According to results Khaykin presented at the AGU meeting, the record-breaking 2023 wildfire season generated numerous pyrocumulonimbus clouds but didn鈥檛 appear to have much of an effect in the stratosphere.
We may know more soon. Researchers at NASA are currently preparing for a to make sense of how they form. This will help them quantify how fires that inject smoke into the stratosphere affect the climate. 鈥淲e have to understand every step in the process that would lead to something like stratospheric aerosol injection,鈥� says at the US Naval Research Laboratory in California, who is leading the mission.
