2014 will be remembered for the range of weather extremes persistent storms that battered the country at the beginning of the year, to record high temperatures at the end of October. Scientists now have evidence that these persistent extreme weather patterns are increasing in their frequency, due to the rapid heating up of the Arctic that is changing the behaviour of the jet stream.

 

 

Dr. Jennifer Francis who is one of the leading scientists in the U.S. studying the relationship between Arctic warming and changes in the jet stream, says: 

 

“The Arctic is generally very cold and the areas farther south are warm and that difference in area between those two areas is really what fuels that vast river of weather moving high over our head that we call the jet stream. 

 

The jet stream in turn creates the weather that we feel all around the northern hemisphere and the middle latitudes, so anything that affects this jet stream is going to affect weather patterns. So as the Arctic warms up much faster than the areas farther south, we’re seeing this temperature difference between these two regions get smaller. This means the force that drives those winds in the jet stream are getting smaller and that means the winds themselves in the jet stream are getting weaker.


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The colour band shows the jet stream moving around the northern hemisphere from west to east. Source: NASA

 

When that happens, the jet stream tends to take a wavier path as it travels around the northern hemisphere and those waves are actually what create the stormy patterns [and] the nice weather patterns. As those waves get larger because of this weakening of those winds of the jet streams, they tend to move more slowly from west to east. That means it feels like the weather patterns are sticking around longer, because those patterns are moving much more slowly and this then makes it more likely to have the kind of extreme events that are related to persistent weather patterns.”

 

Are critical findings influencing policy?

 

These changes in climate have huge implications as Dr. Francis points out, there are “people who worry about whether there is enough fresh water to supply cities, whether there is enough snowpack on mountains to supply reservoirs, and for agriculture… Drought and agriculture is a big problem. Storminess in certain areas is another big problem. Yes, it has a huge impact for a whole range of issues that affect the way we live.”


It is no wonder then that Dr. Francis and her colleagues have attracted the attention of President Obama’s chief science advisor, Dr. John Holdren. Dr. Holdren has been reporting directly to the President on the real time effects of climate change and is keen to understand what this new research tells us about the future impact of changes to the jet stream. Francis muses and says:

 

“Yes, we’ve had a lot of interest from policymakers… I think we’re starting to make a lot of progress now in getting policymakers to understand that this is a big problem they have to face… I think decision makers and the policymakers at the local level get it much better because they’re already seeing effects on their local areas. Sea level rise is an obvious one. They’re already seeing changes in drought and agricultural problems and dealing with fresh water issues. It is really at the local level that we’re having more success.”

 

New research supports the case that Arctic sea ice loss is driving climate changes

 

So in understanding the changes in the jet stream it is important to research how the vast atmospheric river of weather above our heads is connected to other climate mechanisms. To explain this, Francis cites new research by colleagues that has emerged in the last couple of months:

 

“It appears that over the north Atlantic, and towards Asia, there’s a mechanism that appears to be quite robust, and several groups have found this mechanism using completely different analysis techniques. So what we’re finding is that there’s an area, North of Scandinavia in the Arctic, where the ice has been disappearing particularly rapidly. When that ice disappears… there is regular ocean underneath, and that ocean absorbs a lot more energy from the sun through the summertime. So it becomes very warm there. 

 

Then as the fall comes around, all that heat that’s been absorbed all summer long, where the ice has retreated, is put back in the atmosphere and that creates a big bubble of hot air… over that region where the ice was lost. This tends to create a northward bulge in the jet stream there… that  creates a surface high pressure area that circulates in the clockwise direction. That sucks cold air down from the Arctic over northern Eurasia, and that creates a southward dip in the jet stream. So what we’re getting is this big northward bulge up over Scandinavia and a southward dip over Asia… creating, first the tendency for a larger wave in the jet stream, which tends to move more slowly, but also we’re seeing this mechanism that creates these colder winters that have been observed over Eurasia.

 

Once the jet stream gets into this wavier pattern, it sends wave energy up into the highest levels of the atmosphere, which is called the stratosphere, where we have the polar vortex, [which] is kind of similar to the jet stream but it’s much higher up in the atmosphere and it travels much faster. So as that wave energy gets sent up from this larger wave below, up into the stratosphere, it breaks down that polar vortex so that it becomes wavier as well. That wavier polar vortex sends energy back down to the lower atmosphere and it creates an even wavier jet stream in February. So we’re seeing this connection of mechanisms that starts with [Arctic] sea ice loss and it makes a wavier jet stream for different reasons all the way through winter.”

 

Will the jet stream continue to cause changes in climate?

 

By identifying these mechanisms and linking them back directly to loss of the Arctic sea ice, Dr Francis and her colleagues are demonstrating how manmade global warming is creating feedback that is changing the climate conditions in the northern hemisphere. So what next? 

 

[We are] using these climate models, or computer simulations… to try and project what we’re expecting to see happen in the future, as greenhouse gases’s continue to increase.  The early indications are that these large wavy patterns in the jet stream are going to increase in the future, as far as we can tell. It is preliminary research that I haven’t published yet but it does look as if they are going to increase.”

 

Nick Breeze - Climate change film maker and writer


This article was originally published in The Ecologist 
 

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