Researchers have made the link between human activity and extreme winter weather patterns in the western United States.
As climate change worsens, Western North America is experiencing extreme weather whiplashes. Prolonged drought followed by very severe flooding in the winter appears to be becoming the norm. These weather patterns are carried through interconnected pathways around the globe.
Researchers led by Professor of Earth Sciences and Environmental Engineering Jin-Ho Yoon, and including Ph.D. student Jueun Lee from the Gwangju Institute of Science and Technology, initiated a new study to understand better these changing weather patterns. The findings have been published in Nature Research journal Climate and Atmospheric Science.
The researchers studied three major teleconnection patterns that affect winter weather. These are known as the Pacific North American pattern (PNA), the North Atlantic Oscillation (NAO), and the North American winter dipole (NAWD).
Assessing the NAWD over a 70-year period between 1951 and 2020, they found a "strengthening negative correlation" between the PNA and the NAWD, the study reported.
"This projected intensification of large-scale atmospheric circulation in a warming climate is expected to likely escalate extreme hydroclimatic events in mid-latitude regions like California near western North America," Yoon said in a statement.
California and other Western states experienced extreme periods of drought between 2011 and 2015.
However, in 2017, California saw torrential rain and subsequent floods. These kinds of weather patterns are still being seen in more recent years. Up to 2023, California was once again suffering from prolonged drought conditions, until a particularly wet winter caused severe flooding. Although this caused widespread disruption, the state's drought status was lifted.
The study likens the effect to a "network of dominos." This is because one piece "can trigger a chain reaction," causing a "series of unforeseen events."
The changes between the PNA and the NAWD are linked to jet stream variations, the study reported. And as the climate changes and the jet streams vary, these weather patterns alter.
"Climate models consider a range of factors affecting the atmosphere, including changes in greenhouse gas concentrations resulting from human activities. By running simulations with and without the influence of greenhouse gases, we can compare the results and see how they differ," Yoon said.
The researchers also found a correlation between an abundance of greenhouse-gas levels and changes in the jet stream.
They discovered that the greenhouse gases cause a northward drift of the jet core in the Asia-Pacific. The phenomenon causes a strong wave through the Western U.S.
The study reiterates the need for addressing climate change. As greenhouse gases continue to be pumped into the atmosphere, weather patterns will likely continue shifting and causing more extreme patterns.
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