By Sam Carana, with contributions by Jennifer Francis
Global warming is increasing the strength of hurricanes. A warmer atmosphere holds more water vapor and sea surface temperatures are rising. Both of these changes strengthen hurricanes. Steering winds may also be changing, causing unusual hurricane tracks such as Sandy's left turn into the mid-Atlantic seaboard and Harvey's stagnation over Houston. Is rapid Arctic warming playing a role?
Jennifer Francis has long been warning that global warming is increasing the likelihood of wavier jet stream patterns and more frequent blocking events, both of which have been observed. The Arctic is warming more rapidly than the rest of the world. The narrowing temperature difference between the Arctic and lower latitudes is weakening the speed at which the jet stream circumnavigates Earth and may be making the jet stream more wavy. In a 2012 study, Jennifer Francis and Stephen Vavrus warned that this makes atmospheric blocking events in the Northern Hemisphere more likely, aggravating extreme weather events related to stagnant weather conditions, such as drought, flooding, cold spells, and heat waves.
The danger was highlighted later that year, when a strong block associated with a deep jet stream trough helped steered Hurricane Sandy toward New York. In 2017, Hurricane Harvey hovered over Houston and dumped record-breaking rains (over 50 inches in some locations!), again highlighting this danger.
The jet stream separates cold air in the Arctic from warmer air farther south. A wavier jet stream transports more heat and moisture into the Arctic. This speeds up warming of the Arctic in a number of ways. In addition to warming caused by the extra heat, the added water vapor is a potent greenhouse gas, trapping more heat in the atmosphere over the Arctic, while it also causes more clouds to form that also are effective heat trappers.
As the Arctic keeps warming, the jet stream is expected to become more distorted, bringing ever more heat and moisture into the Arctic. This constitutes a self-reinforcing feedback loop that keeps making the situation worse. In conclusion, it's high time for more comprehensive and effective action to reduce the underlying culprit: global warming.
|Jennifer Francis is Research Professor at the Institute of Marine and Coastal Sciences at Rutgers University, where she studies Arctic climate change and the link between the Arctic and global climates.|
Jennifer has received funding from the National Science Foundation and NASA. She is a member of the American Meteorological Society, American Geophysical Union, Association for Women in Science and the Union of Concerned Scientists.
• Evidence Linking Arctic Amplification to Extreme Weather in Mid-Latitudes, by Jennifer Francis and Stephen Vavrus (2012)
• Why Are Arctic Linkages to Extreme Weather Still Up in the Air? By Jennifer Francis (July 7, 2017)
• Amplified Arctic warming and mid‐latitude weather: new perspectives on emerging connections, by Jennifer Francis, Stephen Vavrus, Judah Cohen (May 16, 2017)
• Jennifer Francis: A New Arctic Feedback - interview with Peter Sinclair
• Jennifer Francis - Understanding the jet stream