UGA research links climate change to lazier jet stream, leading to weather extremes

Jet streams are relatively narrow bands of strong wind in the upper atmosphere, typically occurring around 30,000 feet in elevation, that blow from west to east. The normal westerly flow leads to week-to-week variations in the weather, modulated in the mid-latitudes by ridges and troughs in the jet stream.

The influence of a high-pressure ridge, for example, produces clear, warmer weather conditions; a trough in the jet stream is typically followed by stormy conditions. The ridges and troughs that, together, form waves in the jet stream can stall as these waves grow and become more amplified. One impact of the disproportionate warming at high latitudes, particularly in the arctic, that has occurred with climate change could be the jet stream and its westerly flow slowing down, causing stuck weather patterns that produce longer duration storms and longer lasting heat waves.

New research led by the University of Georgia published in Nature Communications describes observations linking the increased warming at high latitudes and the ever-decreasing snow cover in North America to changes in atmospheric circulation.

"That's the question behind of a lot of emerging climate research, whether we are going to expect to see more persistent weather extremes," said Jonathon Preece, postdoctoral teaching and research associate in the Franklin College of Arts and Sciences department of geography and lead author on the study. "These persistent and extreme conditions are thought to be increasing in the future as a result of this increased waviness in the jet stream."

Since 2000, frequent stuck weather where waves in the jet stream are blocked have produced heatwaves over Greenland, resulting in exceptional melting of the Greenland Ice Sheet. In contrast to the observations, global climate models project a slight decrease in the blocked patterns over Greenland and, consequently, the models have underrepresented the contribution of meltwater runoff from the ice sheet to global sea level rise. 

“These patterns have been consistently creating pulses of melting over the Greenland ice sheet that have been accounting for a large portion of the annual melting," said Marco Tedesco, Lamont Research Professor at the Lamont-Doherty Earth Observatory of Columbia University and lead P. I. on the project. "Accounting for such aspect is crucial for anticipating not only how much but how fast Greenland is and will be contributing to sea level rise.”

"One question is whether this a consequence of climate change that we can expect to continue in to the future, at least the near term, that the climate models are failing to resolve. Or are the climate models correct, in which case we'd expect things to revert back to the norm and perhaps the rate of accelerated melt of the ice sheet will taper some," Preece said.

The new study presents evidence of a link to consequences of climate change, and in particular, both the increases in the waviness of the jet stream and the ever-decreasing spring north American snow cover extent.

"We found evidence that increasing waviness of the jet stream together with the decline in North American snow cover is impacting the atmosphere in a way that is favoring these blocked high-pressure systems over Greenland," Preece said.

Multiple studies highlight the discrepancy between climate models and observations. The UGA study provides evidence of a direct link between the observed shift in summer atmospheric circulation over Greenland and amplified warming at high latitudes, which is causing the increased amplitude or waviness of the jet stream and also the decline in terrestrial snow cover. 

"The new research study is the first that we know of that demonstrates a direct link between the observed change in summer atmospheric circulation over Greenland and diminished spring snow cover, which is something we can confidently say is a consequence of climate change," said Thomas Mote, Distinguished Research Professor in geography at UGA and co-author on the paper.

The research is supported by funding from the National Science Foundation, Heising-Simons Foundation, and U.S. Department of Energy. Co-authors on the study include Judah Cohen, head of seasonal forecasting at AER, a Verisk company; Lori Wachowisz, John Knox, and Gabriel Kooperman of the University of Georgia department of geography.

Image: High-pressure ridge over Texas, 2018, via