(CN) — Bushfires in Australia in 2019 devastated the country, burning approximately 46 million acres, harming or killing billions of animals and taking the lives of at least 34 people. And their effects were likely felt across North America, too, according to research published in Science Advances on Wednesday ties the "Black Summer" to a rare multi-year La Niña event.
La Niña is a complex weather pattern that occurs when strong winds push the warm ocean surface waters away from South America and across the Pacific Ocean. As the warm water moves out, cold water from the ocean depths rises to the surface. This phenomenon causes a massive shift in heat over about a quarter of the planet, severely disrupting weather patterns. They follow a similar yet opposite weather pattern called El Niño.
La Niña changes the winters across North America. Canada and northern America get colder, the southwest U.S. gets hotter and drier, and the Pacific Northwest gets wetter. Historically, La Niñas are dormant for years and can be predicted months in advance. However, in 2020, a multi-year La Niña streak began that was not forecasted. It started without a preceding El Niño event, and unusually took place three years in a row.
Research spearheaded by the National Center for Atmospheric Research described in the study published Wednesday draws the connection between the Black Summer and the recent string of La Niñas. Prior research on La Niñas proved that significant volcanic eruptions could trigger one as light-reflecting particles create cooler climates. So scientist John Fasullo, lead author of the study, and his team were curious about the effects of fire emissions on the environment.
“Many people quickly forgot about the Australian fires, especially as the Covid pandemic exploded, but the Earth system has a long memory, and the impacts of the fires lingered for years,” said Fasullo in a press release.
The researchers used the Community Earth System Model version 2, a National Center for Atmospheric Research-based computer model, to run emissions simulations starting in August 2019. The model included some of the early fire emissions detected by satellite. Another simulation was run using average wildlife emissions.
The models showed that the Black Summer was on track to kick off a long line of climate activity. Reflective aerosols clouded the coast of Peru and other areas in the Southern Hemisphere, which in turn cooled the region. Additionally, it caused the meeting point of the northern and southern trade winds to move. These changes crafted the perfect La Niña condition: a cool Pacific Ocean.
The study's authors say well-developed forecasting tools, including a coupled Earth model that utilizes ocean and atmosphere data, are crucial to more accurately predict weather events.
The research also emphasizes the need for realistic wildfire models. Currently, most climate models don’t factor in additional wildfire emission risks, but only account for a predetermined amount. The more dynamic climate modeling systems are, the better scientists can predict events like La Niña.
“As the climate changes, the emissions from wildfires will also change,” Fasullo said. “But we don’t have that feedback in the model. It is the goal of our current work to incorporate these effects as realistically as possible.”
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