This winter has seen significant activity in the stratospheric polar vortex – the powerful cyclonic winds circling the North Pole high in the atmosphere.
The winds have completely reversed direction twice so far. Such disruptions are often linked to extreme weather events like the January cold snap across central parts of the United States. While providing interesting meteorological drama, this vortex behavior also relates to the broader issue of climate change.
“It was a substantial reversal, reaching -20.5 m/s a few days ago, which puts it in the top 6 strongest such events since 1979.” Dr. Amy Butler.
Human-caused climate change isn’t just warming the lower atmosphere near Earth’s surface. It is impacting the entire atmospheric vertical profile, including the stratosphere some 10-50 km above us. As greenhouse gas concentrations increase, this causes cooling in the stratosphere – even as the troposphere below warms. This stratospheric cooling influences the strength and stability of the polar vortex circulation.
Climate models consistently show that continued greenhouse gas emissions and stratospheric cooling will lead to a weakened polar vortex on average over time. This makes major mid-winter warming events like we’ve seen more likely in the future. And when the vortex is disturbed, it increases the chances for atypical weather patterns and extremes at the surface like the intense cold some experienced in January.
So while the polar vortex disruptions energized discussions about the stratosphere’s influence on surface weather, they also provided a window into the climate change signatures emerging higher up. The stratosphere is gradually changing in response to human activities – an important indicator of the widespread atmospheric impacts caused by rising greenhouse gas levels.
Climate change’s complicating factors
Of course, the stratosphere’s response to human influences is complex. It gets further complicated by interactions with other climate patterns and cycles operating across the interconnected Earth system.
For example, this winter’s El Niño event in the tropical Pacific likely increased the odds of a polar vortex disruption. Historical data reveals that sudden stratospheric warming events are nearly twice as likely in El Niño winters compared to neutral conditions. This connection stems from El Niño favoring an atmospheric wave pattern that can destabilize the polar vortex from below.
However, scientists don’t fully understand why similar stratospheric disruptions occur just as frequently during the opposite La Niña phase of the El Niño-Southern Oscillation cycle. There are still knowledge gaps in how these major tropical ocean-atmosphere patterns interact with and perturb the stratosphere.
Additionally, other climate cycles like the solar cycle, quasi-biennial oscillation, and even air pollution levels can all exert influences on stratosphere temperatures and circulation patterns like the polar vortex. Parsing the impacts and isolating the human-caused climate change fingerprint gets complicated with all these different forces in play.
Widening our climate change perspective
Despite the complexities, focusing just on the warming troposphere provides an incomplete picture of climate change’s full effects. We need to widen our perspective.
Changes high up in the stratosphere can in turn feedback down to influence weather patterns near the surface over weeks and months. So stratospheric climate change impacts could manifest as increasing extreme events, disruptions to global circulation patterns, growing risk of ozone hole formation, and more.
This winter has provided a timely reminder about the stratosphere’s importance while also hinting at the emerging climate change signals in this remote atmospheric region. As we strive to better understand the mechanisms and buffers within the interconnected climate system, we must adopt a truly global viewpoint that encompasses the entirety of the atmosphere – from the ground to the edge of space.
Only with this fuller perspective can we anticipate all the ramifications, both intuitive and surprising, that human activities are catalyzing within the thin shell of air sustaining life on our planet. The stratospheric polar vortex is signalling that climate change’s disruptive fingerprints are rapidly spanning the vertical atmosphere as well as the horizontal dimensions we typically envision.
Original source: https://gmao.gsfc.nasa.gov
https://www.animalagricultureclimatechange.org/extreme-weather-the-norm/
