Wildfires are expected to become more frequent and intense in the future. They not only pose a serious threat to humans and ecosystems, but also affect Earth’s atmosphere. Wildfire plumes can reach into the stratosphere, but little is known about their climate impact. Here, we reveal observational evidence that major wildfires can have a severe impact on the atmospheric temperature structure and short-term climate in the stratosphere. Using advanced satellite observation, we find substantial warming of up to 10 K of the lower stratosphere within the wildfire plumes during their early development. The short-term climate signal in the lower stratosphere lasts several months and amounts to 1 K for the Northern American wildfires in 2017, and up to striking 3.5 K for the Australian wildfires in 2020. This is stronger than any signal from recent volcanic eruptions. Such extreme events affect atmospheric composition and climate trends, underpinning their importance for future climate.

Small volcanic eruptions and their effects have recently come into research focus. While large eruptions are known to strongly affect stratospheric temperature, the impacts of smaller eruptions are hard to quantify because their signals are masked by natural variability. Here, we quantify the temperature signals from small volcanic eruptions between 2002 and 2016 using new vertically resolved aerosol data and precise temperature observations from radio occultation. We find characteristic space‐time signals that can be associated with specific eruptions. In the lower stratosphere, robust warming signals are observed, while in the midstratosphere also cooling signals of some eruptions appear. We find that the volcanic contribution to the temperature trend is up to 20%, depending on latitude and altitude. We conclude that detailed knowledge of the vertical structure of volcanic temperature impacts is crucial for comprehensive trend analysis in order to separate natural from anthropogenic temperature changes.

<p>In the future, large wildfires are expected to become more frequent and intense. Not only do they pose a serious threat to people and ecosystems, but they also affect the Earth's atmosphere. Aerosols from large wildfires can even reach the stratosphere where they can linger for months to years. However, little is known about their impact on climate. In particular, the potential of large wildfires to cause temperature changes in the stratosphere has hardly been studied.</p><p>In our study, we analyze two extreme wildfire events, those in 2017 in North America and those in 2019/20 in Australia, using new satellite observational data. We find strong effects of the fires on the atmospheric temperature structure and short-term climate in the stratosphere. The results show significant warming of the lower stratosphere by up to 10 K within the aerosol clouds emitted by the wildfires immediately after their formation. The climate signal in the lower stratosphere persists for several months, reaching 1 K for the 2017 North American wildfires and a remarkable 3.5 K for the 2019/20 Australian wildfires. This is stronger than any signal from volcanic eruptions in the past two decades. Such extreme events potentially influence the atmospheric composition and stratospheric temperature trends, underscoring their importance for future climate.</p><p>Improved knowledge of the temperature signals from extreme wildfires is particularly important for trend analysis. Our ongoing research on this topic aims to further improve the separation of natural variability from anthropogenic influences in climate trend detection, especially in the stratosphere.</p>

<p>Für die Zukunft wird erwartet, dass große Waldbrände immer häufiger und intensiver auftreten werden. Diese stellen nicht nur eine ernsthafte Bedrohung für Menschen und Ökosysteme dar, sondern beeinflussen auch die Erdatmosphäre. Aerosole von großen Waldbränden können sogar die Stratosphäre erreichen und dort über Monate bis Jahre verweilen. Über ihre Auswirkungen auf das Klima ist jedoch nur wenig bekannt. Insbesondere das Potenzial großer Waldbrände, Temperaturänderungen in der Stratosphäre zu verursachen wurde bisher kaum untersucht.</p> <p>In dieser Studie analysieren wir zwei extreme Waldbrandereignisse, jene 2017 in Nordamerika und jene 2019/20 in Australien, mittels neuer Satellitenbeobachtungsdaten. Wir finden starke Auswirkungen der Brände auf die atmosphärische Temperaturstruktur und das kurzfristige Klima in der Stratosphäre. Die Ergebnisse zeigen eine signifikante Erwärmung der unteren Stratosphäre um bis zu 10 K innerhalb der von den Waldbränden ausgehenden Aerosolwolken direkt nach ihrer Entstehung. Das Klimasignal in der unteren Stratosphäre bleibt mehrere Monate lang bestehen und erreicht 1 K für die nordamerikanischen Waldbrände 2017 und bemerkenswerte 3,5 K für die australischen Waldbrände 2019/20. Dieses Signal ist stärker als jedes Signal von Vulkanausbrüchen in den letzten zwei Jahrzehnten. Solche Extremereignisse können die Zusammensetzung der Atmosphäre und die Temperaturtrends in der Stratosphäre beeinflussen, was ihre Bedeutung für das künftige Klima weiter unterstreicht.</p>