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Significant atmospheric circulation changes causing an increase in extreme weather are also potentially occurring because of a wide variety of other human-related factors.
Deforestation alters the location and amount of moisture in the air; it also changes the reflectivity of the planet, altering how much sunlight goes into and out of the atmosphere. Fine particle pollution, called PM2.5, reflects sunlight and encourages cloud formation, causing significant impacts on regional weather. For example, high levels of fine particle pollution emitted from the U.S. and Europe are thought to be the primary cause of an atmospheric circulation change — a southward shift of the tropical rain belt called the Intertropical Convergence Zone — that led to the central African drought of the 1970s and 1980s, which killed over 500,000 people. After legislation to limit such particle pollution was passed in the U.S. and Europe in the early 1990s, the tropical rain belt shifted back to its former state, and the drought lessened. More recently, high emissions of small pollution particles over Asia have been linked to a weakening of the monsoon and an increase in intensity of the Arabian Sea tropical cyclones.
Tornado seasons are becoming more variable
Climate change may be influencing how tornadoes and tornado outbreaks are clustered. Because tornado formation depends on a complex set of ingredients in and around a single thunderstorm, there is no sign that climate change is tending to make tornadoes stronger or weaker on average.
However, it appears that U.S. tornadoes are tending to occur in larger outbreaks more often, with longer “dry spells” in between, not unlike the tendency for rainfall to be concentrated into heavier extremes.
There are also signs that hotter, drier air from the Southwest is helping to shift tornado activity toward the Mississippi Valley and Mid-South, farther east than the traditional Tornado Alley of the Great Plains. This shift has major safety implications, as the Southeast U.S. is more vulnerable to tornadoes than the Plains in several ways, including having a higher likelihood of nighttime tornadoes. And the last several years, including the two devastating tornado outbreaks of December 2021 and the active twisters of January 2023, suggest that a warming winter atmosphere could be allowing for more cold-season tornadoes farther north than they are traditionally observed.
A meteorologist’s perspective
The broad outlines of global climate change have been mapped out since the 1990s, and we are continuing to learn about its many ominous manifestations in extreme weather events.
The picture is not complete, though. In 2004, Harvard climate scientists Paul Epstein and James McCarthy concluded in their paper Assessing Climate Stability: “We are already observing signs of instability within the climate system. There is no assurance that the rate of greenhouse gas buildup will not force the system to oscillate erratically and yield significant and punishing surprises.”
Examples of such punishing surprises include Hurricane Sandy of 2012 and the immense jump in catastrophic western U.S. wildfires in recent years.
As the climate continues to warm and the atmospheric circulation further destabilizes, climate change will increasingly bring low-probability, high-impact weather events — “black swan” events — that no one anticipated. As the late climate scientist Wally Broecker once said, “Climate is an angry beast, and we are poking at it with sticks.”
And sometimes Earth itself will throw a curve ball, as in the eruption of the Hunga Tonga–Hunga Haʻapai volcano in January 2022. Along with producing a spectacular swarm of 400,000 lightning flashes on a single day, it’s possible that this eruption threw enough water vapor into the stratosphere to temporarily alter global circulation patterns and even enhance global warming over the next several years.
We need to anticipate and prepare for a significant increase in extreme weather in the coming years as we head toward half of an Ice Age unit of total climate warming. As we discussed in a post last year, The future of global catastrophic risk events from climate change, a U.N. report found that climate change is steadily increasing the risk of rare extreme events that can kill more than 10 million people or lead to damages of $10 trillion-plus, posing threats of total societal collapse.
The good news is that clean energy and other climate solutions are abundant and available, and we can act with urgency to rein in the climate emergency and stabilize our climate once again.
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