How does smoke from wildfires in the western U.S. change the regional climate?

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Article: Biomass Burning Smoke and Its Influence on Clouds Over the Western U. S.

Authors: C. H. Twohy, D. W. Toohey, E. J. T. Levin, P. J. DeMott, B. Rainwater, … & E. V. Fischer

The area burned by wildfires has been increasing in the western U.S. in recent years and is expected to continue to increase due to climate change. In fact, a large wildfire is currently burning in Sequoia National Park in California, threatening to impact some of the largest and oldest living trees in the world. While wildfires directly impact people, wildlife, and the environment in many ways, a lesser-known impact, involving clouds, can influence the regional weather and climate.

Burning wildfires emit a lot of smoke particles into the air, which can impact air quality and visibility, even hundreds of miles away. Some particles make it high up into the atmosphere and can help form clouds, because in order for clouds to form, the water vapor in the air needs particles to condense onto. The sizes and types of particles that the water condenses onto partially control the properties of the clouds they create. Twohy and coauthors utilized data from research flights into clouds near active wildfires all around the western U.S. in the summer of 2018 to study the properties of smoke-born clouds and theorized how they may be impacting the climate in the region.

The most surprising discovery was how many water droplets these clouds contained! The smoke-born clouds contained about 5 times more water droplets than comparable clouds that formed when wildfires weren’t burning. The water droplets in the smoke-born clouds were also about half the size of the droplets in the non-wildfire clouds. The size and number of water droplets in clouds affect how the clouds interact with solar radiation and how likely they are to create rain. The higher number of droplets within the clouds increases the chances that incoming radiation from the sun will hit a droplet and be reflected back to space. This means less solar radiation reaches the ground, leading to a cooling effect at the surface. Because the cloud droplets are so small, they may have a hard time growing large enough to fall down to the surface as rain. Thus, smoke-born clouds are theoretically less likely to create rainfall.

Scientists have linked abnormally dry ground conditions with the recent uptick in wildfires. So, if the smoke is causing clouds that are less likely to produce rain, this would make the dry conditions worse. There is no question that wildfires are dangerous to humans through the destruction of property and their impacts on air quality; however, fires are essential to the ecosystems of the western U.S., because many of the tree species can only reproduce after a fire. A balance must be found between letting natural wildfires burn and protecting human lives, but indirect effects of these fires on the climate, like those discussed in this article, may make the task of finding this balance a lot more difficult.

How does smoke from wildfires in the western US change the regional climate? by Alyssa Stansfield is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

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