Extreme weather events linked to climate change impact on the jet stream.
Unprecedented summer warmth and flooding, forest fires, drought and torrential rain — extreme weather events are occurring more and more often, but now an international team of climate scientists has found a connection between many extreme weather events and the impact climate change is having on the jet stream.
"We came as close as one can to demonstrating a direct link between climate change and a large family of extreme recent weather events," said Michael Mann, distinguished professor of atmospheric science and director, Earth System Science Center, Penn State.
However, while the models are useful for examining large-scale climate patterns and how they are likely to evolve over time, they cannot be relied on for an accurate depiction of extreme weather events.
These conditions occur when the jet stream, a global atmospheric wave of air that encompasses the Earth, becomes stationary and the peaks and troughs remain locked in place.
The jet stream can then behave as if there is a waveguide — uncrossable barriers in the north and south — and a wave with large peaks and valleys can occur.
However, when these temperature gradients decrease in just the right way, a weakened "double peak" jet stream arises with the strongest jet stream winds located to the north and south of the mid-latitudes.
The researchers looked at real-world observations and confirmed that this temperature pattern does correspond with the double-peaked jet stream and waveguide patter associated with persistent extreme weather events in the late spring and summer such as droughts, floods and heat waves.
They found the pattern has become more prominent in both observations and climate model simulations.
"We are now able to connect the dots when it comes to human-caused global warming and an array of extreme recent weather events," said Mann.