VIDEO: The Jet Stream, Extreme Weather and Climate Change

Summary

Climate change is playing two different roles in the string of astonishing record-breaking weather observed across the globe over the past two weeks. 1) The overall warming driven by carbon pollution is amplifying heatwaves, helping to push them past historic levels. 2) Climate change is increasing the frequency of unusual jet stream configurations, such as the one driving the current extreme heat.

Climate scientists Jennifer Francis, Michael E. Mann, and Noah Diffenbaugh discuss these connections with Markeya Thomas of Climate Signals.

Highlights

Noah Diffenbaugh, geoscientist and Professor of Earth System Science at Stanford University:

• Overall globally what we’ve been seeing is exactly what has been predicted for decades. The warming of the planet as a whole is leading to warming of individual regions. The warming of the individual regions is upping the odds that when these heat waves happen that they’re hotter and more severe. It’s upping the odds that the atmospheric and ocean conditions that create heat waves, that when those conditions occur, they produce more severe events and in some cases more prolonged events.
• What we find is that global warming has already put a thumb on the scale for a number of different kinds of extremes.
• Around the world, we find a human fingerprint of global warming at more than 80% of the surface area of the globe for the hottest temperature on record. For the hottest heat event, global warming has already put a thumb on the scale at more than 80% of the world.

Mike Mann, climate scientist, Penn State:

• It’s not rocket science, you make the earth hotter you’re going to have more extreme heat. You’re going to have longer periods of extreme heat, you’re going to have more intense heat, and that’s what we’re seeing.
• Climate change, and in particular, the melting of the Arctic sea ice and the warming of the Arctic is actually changing the jet stream in a way that leads to more persistent extreme meanders in the jet stream in the summer. That gives us these blocking high pressure systems where we see intense heat. It gives us these troughs, these low pressure areas that stay put day after day that give us excessive rainfall and extreme flooding. So, it isn’t just that a warmer planet is warmer, it’s changing the atmospheric circulation in a way that may be giving us these very persistent extreme events.
• One of the real threats of heat waves is not just the hot temperatures we see in the daytime, but the fact that night temperatures don’t drop to comfortable levels, to levels that allow us to sleep comfortable. It actually becomes a severe health threat, especially for the elderly and the young, when temperatures don’t cool down your body doesn’t have a chance to recuperate from the extreme heat that you’ve experienced during the day time.
• In reality, climate change is also changing the behavior of the jetstream. It’s changing the atmospheric circulation. It may be leading to more of these blocking high pressure systems that remain stationary. That’s when you get unprecedented heat spells, when the same high pressure region covers Europe or North America, day after day, and the sun continues to bake those regions.
• Higher global temperatures mean more intense heat periods, more extended heat periods and we’re changing the atmospheric flow in away that gives us those stagnant air masses that are associated heat like what we’ve seen in Europe this week.

Jennifer Francis, climate scientist at Rutgers:

• We’ve also seen the jet streams split over North America and over Europe. If you look at the map of the jet stream today, or anytime over the last week or two, you’ll see this split characteristic has been there. And when I say split, I mean part of it is going to the North and traveling along the coast of the Arctic and the other part is further south. Some of Mike’s research and and his colleagues have suggested is that when the jet stream does this split type of a feature, it tends to trap the weather patterns, the weather systems between those splits and makes them very stagnant and persistent. They’ve connected that to a lot of the most extreme events we’ve seen over the last couple of decades. That kind of mechanism seems to be playing a role and increasing over time.
• Some of the impacts of these extreme events are unfolding and starting to affect people, and the ecosystem, in very expensive and damaging ways. If there’s any silver lining to this dark cloud, it would be that I think more and more people now are recognizing that the impacts are affecting them personally.
• It’s costing people money, it’s costing people lives, it’s costing their own property and climate change is affecting people today. It’s not a distant problem for their grandchildren.
• When you’ve got one kind of extreme in one place, most likely you’re going to find extremes of other types also occurring at the same time because of these … in the jet streams.
• Those waves in the jet streams, those north-south swings in the jet stream are what create the weather around the northern hemisphere that we all experience down at the surface. When it’s crazy and bizarre in one place, like a heat wave in one area, you can bet somewhere else it’s overly cold. Which in the summer it doesn’t get reported because everybody’s happy about that. You’ll also find areas that get persistent rain, and that’s been happening for example along the Atlantic seaboard. Washington, DC has been under water the last couple of weeks.