Friday, August 23, 2013

Getting Knotted: Climate Change and the Jet Stream

Eli has been amongst those concerned with links between Arctic heating, jet stream perturbations and weird weather.  Eli, of course, is neither a meteorologist nor a climate scientist, he is but a bunny, but a literate one (unusual, we know) and has been following work in this area, led by Jennifer Francis at Rutgers.  Just yesterday the Rabett ran into three things that tied all this together.  First Paul Douglas shows Eli a weather forecast map from NOAA, where nature has turned it up to bake in the north central US.  Unusual for this time of year, but especially so because it was freezing cold for the summer just weeks ago

 Next a map of the jet stream from Intellicast

And finally an editorial in Nature Climate Change which ties the package together
The day-to-day weather and longer-term climate are different phenomena, although there are strong links between them. The interplay between the many facets of the climate system can have big impacts in the short term, affecting the weather. Take for example the northern jet stream — a key determinant of weather patterns in the Northern Hemisphere and a hotly discussed topic in Europe and the US. Climate scientists who gathered at the UK's Met Office in June pointed the finger of blame at variation in the Atlantic multi-decadal oscillation for a succession of washout summers, as had previously been noted by Rowan Sutton and Buwen Dong (Nature Geosci. 5, 788792; 2012). The meeting also highlighted that a shift in the jet stream contributed to Europe's unusual seasonal weather over recent years.

The jet stream is driven by climate; it is created by the temperature difference between the cold Arctic region and the warmer low latitudes. When there is a large disparity, the jet stream is stronger and faster, meaning it runs straighter. However, the temperature difference has decreased in recent years because the Arctic is warming more rapidly than the rest of the planet, resulting in a weaker and slower jet stream.
The decreased jet stream speed results in large north–south meanders. It is these shifts that produceunseasonal weather patterns over Europe/the Northern Hemisphere. If the jet stream sits to the north it brings the warm weather from the lower latitudes. Conversely, if the jet stream meanders to the south it can bring unsettled weather and colder temperatures.
It is only the linkages, the uncovering of the physical mechanisms tying together Arctic warming, jet stream wander and weird weather in the Northern Hemisphere that allow one to say there are good reasons for suspecting that they are all associated with people's burning of fossil fuels in the last century.  Of course fingerprint studies and more suffering will be necessary to more firmly establish that link.  As Dirty Harry would say: "Is climate change really happening?  Well, to tell you the truth, in all this excitement the Bunny kind of lost track himself. But being greenhouse gases are the most powerful forcing we know, and the best science predicts disaster ahead, you’ve got to ask yourself one question: Do I feel lucky? Well, do ya, punk?"

Take a look at the video of Prof. Francis explaining the Jet Stream meander first before placing your bets


Anonymous said...

I have been following the jet stream waviness over Europe, and it has seemed to fit with teh weather.

However, a paper by Elizabeth Barnes takes on Jennifer Francis' hypothesis, and Kevin Trenberth has also been sceptical (in the correct sense of the word).


Anonymous said...

File under: GHG as .44 Magnum.

Similarly, Harry also once offered this advice to the "skeptics":


Susan Anderson said...

Thank you for this post. I had noted the Barnes paper, but think we will have to wait and see on this.

One thing is that for the not totally science illiterate but hardly literate either types like myself, the whole thing makes so much sense. However, one does not want to be a dear little nut and get ahead of oneself.

Anonymous said...

1. The zonal index is somewhat 'self-modulating'. Waves in the jet stream effect heat distribution in ways that lead to zonal flow of the jet stream ( and vice versa ).

2. On 'average', no precipitation would fall in places like the American Southwest. It is precisely the irregular undulations of the jet stream that leads to precipitation events.

3. Changes in the jet stream are not far fetched, but 'normal' evidently would include the range of changes that led to the 'Dust Bowl'.