Scientists have successfully simulated the full life cycle of wildfire-driven thunderstorms, known as pyrocumulonimbus (pyroCb) events, within a global Earth system model for the first time. This breakthrough, achieved by researchers at the Department of Energy’s Pacific Northwest National Laboratory, allows for a more accurate representation of the significant impacts these extreme weather events have on the Earth’s atmosphere and climate system.
The ability to model pyroCbs is a critical step forward in understanding their far-reaching consequences. These storms, generated by the intense heat of large wildfires, can inject massive amounts of smoke and aerosols high into the stratosphere, where they can linger for over a year. The presence of these particles can lead to the depletion of the ozone layer, affect global weather patterns, and alter the Earth’s energy balance. By incorporating the complex physics of these events into climate models, scientists can now better predict their frequency and effects in a warming world.
Modeling Extreme Smoke Plumes
The research team utilized the Department of Energy’s Energy Exascale Earth System Model (E3SM) to achieve this modeling milestone. A key innovation was the development of a simplified plume rise model that could be integrated into the broader climate model framework. This sub-model simulates the rapid vertical transport of smoke from a wildfire, a process that was previously too computationally intensive to include in global simulations. The model was specifically designed to represent the conditions observed during the 2017 British Columbia wildfire season, which produced some of the most well-documented pyroCb events.
Simulating Stratospheric Injection
The simulations successfully recreated the injection of smoke into the stratosphere, reaching altitudes of over 12 miles. The model showed how the smoke particles, once in the stratosphere, were heated by sunlight, causing them to rise even higher. This self-lofting phenomenon is a crucial aspect of pyroCb events, as it determines the longevity and global distribution of the smoke plume. The model’s output closely matched satellite observations of the 2017 event, confirming the accuracy of the new simulation capabilities.
Impacts on the Ozone Layer
One of the most significant findings of this research is the modeled impact of pyroCb events on the Earth’s protective ozone layer. The simulations demonstrated that the smoke particles can lead to the depletion of ozone in the stratosphere. This occurs because the surface of the smoke particles provides a reaction site for chemicals that destroy ozone molecules. The model showed a significant reduction in ozone concentrations within the smoke plume, a finding that aligns with observations from recent major pyroCb events, such as the 2019–2020 Australian wildfires.
Chemical Reactions in the Stratosphere
The model included detailed atmospheric chemistry to simulate the complex interactions between smoke particles and ozone. The researchers found that the smoke aerosols led to an increase in the levels of reactive chlorine in the stratosphere, a key ingredient in ozone depletion. The model also showed that the smoke particles absorbed solar radiation, leading to localized heating that further altered atmospheric chemistry and dynamics. These findings highlight the importance of including aerosol-chemistry interactions in climate models to accurately predict the future of the ozone layer.
Advancing Climate Model Capabilities
This study represents a major advancement in the field of climate modeling. By successfully simulating pyroCb events, scientists can now investigate the feedbacks between wildfires, atmospheric composition, and climate change in a more comprehensive way. The new modeling capabilities will allow researchers to explore how the frequency and intensity of pyroCbs might change in the future, as well as their potential impacts on global climate patterns. This is particularly important as climate change is expected to lead to more frequent and intense wildfires in many regions of the world.
Future Research and Implications
The ability to model pyroCbs opens up new avenues for research. Scientists can now use these models to study the long-term effects of these events on the climate system, including their influence on cloud formation, precipitation, and global temperatures. Future work will focus on refining the model to include a wider range of wildfire conditions and to better represent the microphysics of smoke particles. This research is essential for developing effective strategies to mitigate the risks associated with wildfires and for making more accurate projections of future climate change.
Improving Predictive Accuracy
By improving the representation of extreme events like pyroCbs, scientists can enhance the predictive accuracy of climate models. This will lead to more reliable projections of future climate change, which are crucial for informing policy decisions and for helping society adapt to a warming world. The ongoing development of Earth system models, like E3SM, will continue to push the boundaries of our understanding of the complex interactions that govern the Earth’s climate.