The impact of burning fossil fuels on today's extreme weather

Posted Nov 1, 2018 by Karen Graham
A new study warns that the continued burning of fossil fuels will likely lead to even more extreme summers than that of 2018 because of its impact on the jet stream.
The speed and waviness of the northern jet stream  a river of wind across the Northern Hemisphere  i...
The speed and waviness of the northern jet stream, a river of wind across the Northern Hemisphere, is affected by the temperature difference between the Arctic and mid-latitudes.
In a study published in Science Advances October 31, Michael Mann, professor of atmospheric science and director at Penn State University, along with an international team of climate scientists, identified how the faster warming of the Arctic twists the jet stream into an extreme pattern that leads to persistent heat and drought extremes in some regions, with flooding in other areas.
The team's research suggests that summers like 2018, when the jet stream drove extreme weather on an unprecedented scale across the Northern Hemisphere, will be 50 percent more frequent by the end of the century under "business-as-usual carbon emissions." In a worst-case scenario, the study predicts a near-tripling of extreme weather events.
The researchers used climate models to predict changes in the occurrence of so-called Quasi-Resonant Amplification (QRA) events associated with persistent weather extremes. Like we experienced earlier this year, the extreme changes in the jet stream brought about flooding, drought, and wildfires.
The extreme weather during the summer of 2018 included flooding in Japan, record heat waves in North America, Europe, and Asia, wildfires in British Columbia, Canada, in Greece and even parts of the Arctic. Heat and drought in California led to the worst wildfire season ever recorded.
The  extremely wavy pattern  called  quasi-resonant amplification   was evident during the extreme s...
The extremely wavy pattern, called "quasi-resonant amplification," was evident during the extreme summer of 2018, Mann said.
Michael Mann
What's with the jet stream and extreme weather events?
When the QRA events occur, the jet stream goes on a meandering north-south course and ends up becoming stationary with the peaks and troughs locked in place. This is not good, obviously.
"Most stationary jet stream disturbances will dissipate over time," said Michael Mann, distinguished professor of atmospheric science and director, Earth System Science Center. "However, under certain circumstances, the wave disturbance is effectively constrained by an atmospheric waveguide, something similar to the way a coaxial cable guides a television signal. Disturbances then cannot easily dissipate and very large amplitude swings in the jet stream north and south can remain in place as it rounds the globe."
"If the same weather persists for weeks on end in one region, then sunny days can turn into a serious heat wave and drought, and lasting rains can lead to flooding," said Stefan Rahmstorf, Potsdam Institute for Climate Impact Research (PIK), Germany.
The banks of the Rhine river near Lobith in the Netherlands have been dried out by the ongoing droug...
The banks of the Rhine river near Lobith in the Netherlands have been dried out by the ongoing drought
Jasper Juinen, ANP/AFP/File
Mann points out this year's climate change impacts were not subtle, instead, smacking us in the face. "It played out in real time on our television screens and newspaper headlines in the form of an unprecedented hemisphere-wide pattern of extreme floods, droughts, heat waves and wildfires," Mann added.
How the QRA plays a role
Mann and his colleagues, in previous work, showed the connection between extreme climate events and climate-induced changes in the jet stream. While researchers cannot accurately identify QRA events in climate models, one thing the climate models capture very well is temperature change.
"QRA events have been shown to have a well-defined signature in terms of the latitudinal variation in temperature in the lower atmosphere," explained Mann. "The change in temperature with latitude and how it responds to increasing greenhouse gas concentrations depends on physics that are well understood and well represented by the climate models."
File photo: North Carolina Army National Guardsmen (NCNG) and local emergency services assist with t...
File photo: North Carolina Army National Guardsmen (NCNG) and local emergency services assist with the evacuation efforts in Fayetteville, N.C., on Friday, Oct. 08, 2016. Heavy rains caused by Hurricane Matthew led to flooding as high as five feet in some areas.
Staff Sgt. Jonathan Shaw/ U.S. Army National Guard
The researchers did find that a pattern of amplified Arctic warming - called Arctic Amplification - did slow down the jet stream while increasing the frequency of QRA episodes.
Aerosol's effect on regulating temperatures
Mann and his colleagues say we must not limit our focus to greenhouse gasses when talking about climate change. Today, the U.S. and Europe have switched to "cleaner" coal-burning methods or done away with coal-fired plants. But countries in other parts of the world have not done this.
If these countries, through mid-century, switch to cleaner coal-burning technology, then the mid-latitude areas of the world will warm and Arctic Amplification will diminish.
China is the world's biggest polluter and has faced an uphill battle transitioning from coal  w...
China is the world's biggest polluter and has faced an uphill battle transitioning from coal, which is used to generate roughly three-quarters of its power
Other pollutants play a big role in the jet stream's behavior, especially aerosols—microscopic solid or liquid particles from industry, agriculture, volcanoes, and plants. "Aerosols have a cooling effect that partially counteracts the jet stream changes caused by greenhouse gases," said co-author Dim Comou, a climate and extreme weather researcher at the Potsdam Institute for Climate Impacts Research and the Vrije Universiteit Amsterdam.
"The future is still very much in our hands when it comes to dangerous and damaging summer weather extremes," said Mann. "It's simply a matter of our willpower to transition quickly from fossil fuels to renewable energy."