New study links carbon pollution to extreme weather
Human activities are altering the jet stream, which leads to extreme weather patterns getting stuck in place
Friday 7 April 2017 06.00 EDT
It was only a few weeks ago that I wrote about changes to extreme weather in a warming world. That prior article dealt with the increase of extreme precipitation events as the Earth warms. I termed the relationship a thermodynamic one; it was driven by local thermodynamic processes. But extreme weather can also occur because of large-scale changes to the atmosphere and oceans. This issue is the topic of another just-published paper that makes a convincing case for a whole new type of influence of humans on extreme weather. In a certain sense, this study confirms what was previously reported here and here. With the march of science, the tools, methods, and evidence get better each year.
Before getting into the study, a little background. The jet stream(s) are high-speed rivers of air that flow in the upper atmosphere. There’s more than one jet stream; they blow west to east and they mark the separation of zones of different temperatures. A good primer on jet streams is available here.
If you were to stand at the northern pole and travel southwards, you would experience a gradual increase in temperature. However, when you reached the first jet stream (the Polar Jet), temperatures would rapidly become warmer. That is, the Polar Jet separates two different temperature air regions. Typically, if you are north of the jet stream, you are in a colder zone whereas if you are south of the stream, it is warmer. Sometimes, the jet streams undulate as they encircle the planet and these undulations move. So, sometimes you happen to be in a position north and sometimes south of the stream, even though your location is fixed.
The interface between warm and cold temperatures creates a lot of weather-pattern changes. In addition, if the undulations of the streams become fixed, it means your weather patterns will get stuck. For instance, you could find yourself in an upward undulation for weeks or longer and experience warm and potentially dry weather. Alternatively, if your location is north of a stuck jet undulation, you may experience persistent cold weather. Perhaps even more importantly, these stuck waves can become larger in their magnitude.
So, scientists really want to know what affects these undulations – both their magnitudes and their persistence. We also want to know whether these undulations will change in a warming planet. This is precisely where the new study comes in. The researchers used both weather observations and climate models to answer these questions. What they found was very interesting.