From the surging polar vortex to unprecedented flooding and fires on every continent, the Earth’s ventilation system is clearly out of whack.
When was the last time you sat on the grass watching clouds drift peacefully across the sky? Can’t remember? Though it’s easy to take those lofty billows for granted, now might be the occasion for a second look.
For clouds are driven by wind and the winds are increasingly affected by global warming and climate change. In fact, some less-than-peaceful winds have recently pushed the frigid polar vortex into the Midwest, whipped up catastrophic cyclones in Mozambique, and pummeled India with erratic monsoon seasons that devastate millions of farmers. Even airplanes are being rocked by unusual supersonic jet streams.
In a sense, it’s simple physics. Like a giant engine, the sun heats Earth with solar radiation. Temperature and pressure differences drive the “fan.”
On Earth, the highest temperatures occur at the equator where warm air rises into the atmosphere and moves toward the poles as a low-pressure system. At the same time, cool air from the poles is drawn toward the equator as a high-pressure system. In general, winds tend to blow from high to low pressure areas.
It’s a planetary air circulation system that has been very consistent and mostly reliable—despite occasional nudges from El Niño and La Niña—one that modern mariners still use to navigate the globe.
Recently, however, these wind currents have begun changing in unpredictable ways that sometimes defy scientific models. The outcome is confusing, complicated, and life-altering for people in every nation of the world.
According to Von Walden, professor of civil and environmental engineering and a member of the Laboratory for Atmospheric Research at Washington State University, these capricious winds are now the subject of an emerging area of research called atmospheric dynamics.
Although it is not his field of expertise, Walden has an interest in wind dynamics, especially the polar vortex and how it could affect his ongoing polar meteorology research. Over the years, Walden has conducted studies in the Arctic and Antarctic regions and is now leading a long-term National Science Foundation project at Summit Station in Greenland.
One of his top concerns is the fact that the Arctic is warming twice as fast as anywhere else on Earth, causing sea ice to melt at unprecedented rates.
Walden begins by describing three basic categories of wind. The first are the surface winds that we experience every day as frontal weather. Next, reaching up to about six miles in altitude, are the tropospheric winds. These include the trade winds in the tropics and westerly winds in the mid-latitudes.
At the boundary between the troposphere and stratosphere, five to nine miles above Earth’s surface, come the jet streams—high-powered wind currents that can reach more than 275 miles per hour. There is usually little turbulence at this height making it a sweet spot for commercial airline travel.
Walden says jet streams occur due to the large temperature difference between the warm lower latitudes and bitter cold polar regions. That difference creates a sharp contrast in air pressure which drives the winds.
Since we live on a spinning planet, those winds are countered by the Coriolis force, causing jet streams to blow from west to east. Earth has four jet streams—a subtropical jet and a polar-front jet in each hemisphere.
The polar vortex is the northern hemisphere’s polar-front jet stream, says Walden. “It’s always been there. It didn’t just appear one day. But we believe the polar vortex is changing because of climate change.
“Before humans caused global warming, we had an extremely cold north pole and a very strong jet stream going around that pole. It was very circular as the temperature differences were greater then. Those strong circular winds held the polar vortex in place for the most part.
“Now, as the Arctic warms faster than anywhere else on Earth—and it’s scientifically measurable—the temperature difference between the north pole and mid-latitudes is decreasing,” he says. “The Earth adjusts and the winds aren’t as strong.
“As a result, the jet stream gets lazy and begins to have big fluctuations and gyrations. It’s not so circular anymore and winds go way north and way south and those changes in polar vortex cause interesting weather events in certain areas.
“On the news we hear about the polar vortex making it very cold in Chicago for example. When I hear that, I’m always thinking it’s really warm somewhere else in the Arctic. Polar air is being allowed to slip down south, but somewhere else in the Arctic, there’s a big blob of warm air going north. You can’t just look at your one location—you need to look at the entire northern hemisphere.
“Climate change is like loading the dice to see more of these types of unusual weather events in the future,” Walden says. “As greenhouse gases accumulate and the climate adjusts in response, the probability of these events increases.”
Cluttering up the atmosphere with carbon dioxide, ozone, and other greenhouse gases has been shown to influence wind patterns but many other factors contribute to a very complex equation—for one, natural aerosols.
Alex Guenther (’86 MS, ’89 PhD), an atmospheric chemist at the University of California, Irvine, collaborates with hundreds of other specialists around the world to solve questions concerning climate, air pollution, and related phenomena.
Guenther previously worked for the National Center for Atmospheric Research and contributed to the Intergovernmental Panel on Climate Change (IPCC)—the leading body of experts on the state of climate change science. The IPCC is run by the United Nations and is dedicated to “providing the world with an objective, scientific view of climate change; its natural, political, and economic impacts and risks; and possible response options.”
Guenther also spent a few years at the Pacific Northwest National Laboratory in Richland where he developed the Model of Emissions of Gases and Aerosols from Nature or MEGAN. MEGAN measures natural environmental emissions and is used by the Environmental Protection Agency and included in virtually all climate models.
“It’s not just cars and factories that emit chemical gases and particles into the air,” Guenther says. “Everything on the planet contributes to the composition of the atmosphere including plants, dust, and salt from the oceans.
“Some of the same types of compounds you’d get from the tailpipes of cars are emitted from trees and other vegetation. Pine needles, for example, emit a volatile organic gas or terpene that you can smell when you’re walking in the forest.” In fact, Guenther says about 80 percent of global organic aerosol precursors in the atmosphere are generated by natural emissions.
“In a clean, pristine environment, the compounds emitted from trees don’t have a negative impact,” he says. “But in a polluted atmosphere, these volatile organic compounds can form substances that affect both the ability of sunlight to reach the Earth’s surface and for Earth’s energy and heat to pass back out into space.”
Though greenhouse gases continue to rise and smog remains a major problem in cities such as Dallas and Los Angeles, Guenther says overall levels of pollutants like ozone and smoke-stack particles are dropping in the United States and Europe thanks to diligent clean-up efforts. As a consequence, the percentage of natural emissions is on the rise.
“When you get down to these low pollution levels, natural emissions become very important in determining the strategies we use to protect air quality,” he says. “In essence, these plant compounds act as fuel that can be ignited by air pollution.
“When you burn fossil fuels, you release a lot of nitrogen oxides (NOx) into the atmosphere. Plant terpenes and other compounds interact with NOx to change the chemistry of the atmosphere and produce ozone and particles, all of which eventually affect the climate and, in turn, the wind patterns.”
Guenther is currently studying atmospheric chemistry in remote areas of the Amazon jungle and Australia, which have recently experienced record-breaking heat, drought, and fires. Closer to home, he and his colleagues are investigating curious air pollution patterns in southern California.
“The strategies to clean up the air in L.A. had been working and pollution levels were consistently dropping year by year,” he says. “But recently, it hasn’t dropped and ozone levels actually have gone up a bit, even when you exclude periods influenced by wildfire smoke. And it’s not clear why.
“According to models, it looked like pollution levels should be dropping as they reduce nitrogen oxides in the air. So, government agencies are very interested in finding out why. One thing that seems likely is the droughts we’ve been having here. We’re thinking the droughts and heat are having an impact.”
Guenther isn’t the only researcher scratching his head over climate trends that deviate from previously reliable models and predictions. On the other side of the world, climate scientists like Deepti Singh untangle a puzzling ball of factors causing misery for the people of South Asia.
Originally from India, Singh is now an assistant professor in the School of the Environment at WSU Vancouver, where she investigates alarming shifts in the South Asian monsoon season. Approximately 1.8 billion people rely on these warm summer rains for their water supply, so unexpected variations can be a matter of life or death.
“All agricultural activity is triggered by the start of the monsoon, which brings about 80 percent of the area’s total rainfall,” Singh says. “Most farmers in India, Pakistan, Bangladesh, and neighboring countries wait till the onset to start planting crops. They also rely on the monsoon to replenish rivers and wells.”
Singh says the arrival of the summer monsoon is the result of a seasonal reversal of wind patterns that is triggered by a seasonal reversal of temperature gradients.
During winter, the Indian Ocean is slightly warmer than the land, causing winds to blow toward the sea. As land heats up during summer, often exceeding 120 degrees Fahrenheit, the winds change direction carrying moisture-laden ocean air inland where it is released as monsoonal rainfall.
Since about 1950 however, this temperature gradient has steadily weakened causing a subsequent weakening of the monsoon and decline in rainfall, says Singh. Yet curiously, there’s been a recent uptick in precipitation.
“It’s interesting because if you look at the last 10 to 20 years, you see a rapid increase in temperatures from global warming,” she says. “But when you look long term, from 1950 to 2000, you see a slight cooling trend over that part of the subcontinent during monsoon season specifically.
“It’s confusing as generally greenhouse gases cause warming everywhere. But over South Asia, we have some really complicated processes going on. There are other human activity factors involved that could be responsible for that cooling trend.”
One culprit is the massive amount of man-made aerosols in the atmosphere—the tiny particles released from burning coal and other fossil fuels. The level of aerosol pollution over South Asia is the highest in the world besides China. In addition, the region claims the world’s most intensive use of irrigation, especially in northern India.
“Irrigation can have a pretty substantial cooling effect on climate in the area,” says Singh. “Some people are even toying with the idea of using it as a mitigation strategy for global warming, though groundwater depletion is a concern.”
On a deeper and more ominous level, Singh says the monsoon rains have grown increasingly erratic with devastating consequences. “We’ve seen a trend toward extreme precipitation—widespread intense rainfall events plus an increased frequency of drought between the intense rainfall.”
The changes also affect Africa and other regions. The South Asia monsoon system is a large-scale wind pattern that extends to the Horn of Africa and is part of a global monsoon system that affects Asia, Africa, Australia, and parts of the Americas.
And because the Indian Ocean has experienced some of the strongest warming trends, monstrous storm systems—like the cyclones that hit Mozambique and Malawi earlier this year—are becoming more frequent in the region.
Such ferocity was on display last July when South Asian cities, including India’s financial capital, Mumbai, were overwhelmed with the heaviest monsoon flooding in a decade.
“The Himalayan areas of northern India, Pakistan, and Nepal also had some really intense flooding that affected millions, causing massive amounts of damage and many deaths,” says Singh. “The impacts are especially dangerous for the masses of vulnerable people living in slums or refugees forced to flee the Rohingya crisis in Myanmar.”
At the same time, severe drought has parched crops, caused despair, and contributed to an alarming farmer suicide crisis in India, she says. “Every year, during and after monsoon season, there are reports of hundreds of farmers taking their lives because they were affected by consecutive crop failures or poor yields.”
Most models suggest these violent and unpredictable weather events are likely to worsen in the future as greenhouse gases continue to rise.
“We know the cyclone systems get stronger with warmer oceans as they cause more rainfall and become more destructive,” says Singh. “We’re also likely to see more severe droughts simply because as temperatures get warmer, it generally affects the severity of droughts.
“Although the overall monsoon circulation is likely to weaken due to changes in temperature gradients, that doesn’t necessarily translate to a weakening of the monsoon rainfall,” she says.
“A warmer atmosphere holds more moisture which can compensate for the weakening circulation. So, there is quite a bit of uncertainty about which of these competing effects will win.”
All this unpredictability leads back to Walden and the fact that the Arctic is warming twice as fast as the rest of the world. He says it’s due to something called Arctic amplification, and clouds are playing a role.
In 2015, Walden spent a month with a group of international scientists aboard the Norwegian research ship, the Lance, in the Arctic Ocean. There, as the Fulbright Distinguished U.S. Arctic Chair, he collected atmospheric data including measurements of clouds in an attempt to determine the causes of thinning sea ice.
“Imagine we have an ice-covered Arctic Ocean—and ice is very reflective of sunlight,” he says. “Now, start warming up the Arctic and the ice melts, exposing ocean water which is very good at absorbing solar radiation. This causes more warming, which melts more ice and exposes more seawater which absorbs more sunlight which melts more ice and exposes more ocean. The process continually feeds back on itself—it amplifies.”
Recent scientific analysis, including Walden’s Arctic Ocean and Greenland research data, showed that clouds forming in the Arctic contribute a surprising amount to the balance of energy at the polar surface. Clouds, they found, add to the warming trend, especially in fall and winter.
Walden says that although it is an extremely complex process, the earliest climate models constructed in the 1980s and early 1990s largely predicted Arctic amplification. “We’ve known this for a very long time,” he says. “We’re seeing that trend year after year, for example, with the extensive melting of Greenland ice last summer.
“And, as Arctic amplification continues—and temperature and pressure gradients shift— we’re loading the weather dice for Category 5 hurricanes, a bad fire season, and other extreme events.”
He pauses. “Yet, you can’t say one fire season or the next was caused by climate change as it may have naturally done that anyway. It’s confusing for some people to understand that we can’t necessarily tie a weather event directly to climate change. And, if we can’t do that, why are we predicting anything?
“Let’s put it this way—say I’m driving through Montana with its 80-mile-per-hour speed limit and choose not to wear a seat belt. There’s a chance I’ll be fine but, if I do get in an accident, what’s the likelihood I’ll get hurt without a seat belt versus wearing one? We all know that my odds are not very good. I’ve loaded my possible injury by not having a seat belt and also by going 80 instead of 60.”
Walden laughs. “It’s not like you couldn’t drive across Montana and be just fine but you’re not as safe without a seat belt.
“So, this is definitely the way climate change works. Through past evidence of how the Earth has responded plus future climate modeling, we believe that as greenhouse gas increases and the planet warms, we’re loading the dice for certain weather events to occur—like dry hot conditions in summer, more rain during winter, less snow, low sea ice, and of course, more frequent visits from the polar vortex.”