Jet stream moved northwards 270 miles in 22 years; climate change to blame?

By: Dr. Jeff Masters , 4:11 PM GMT on June 05, 2008

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Climate change is forcing the jet stream higher and closer to the pole in both the Northern and Southern Hemisphere, according research published this April in the journal Geophysical Research Letters. In their paper, "Historical trends in the jet streams", researchers Cristina Archer and Ken Caldeira of Stanford's Carnegie Institution of Washington analyzed data from 1979-2001, and found that the Northern Hemisphere jet stream moved northward at approximately 125 miles per decade (270 miles during the 22-year period of the study). The jet moved higher by 5-23 meters during this period, and the wind speeds decreased by about 1 mph. Archer and Caldeira's study confirms other research showing a poleward movement of the jet stream in recent decades (Fu et al., 2006; Hu and Fu, 2007). All of these changes are consistent with the behavior of the jet stream predicted by global warming theory. For example, Lorenz and DeWeaver (2007) found poleward shifts of the jet stream by 2100 in the forecasts of 15 climate models used to formulate the "official" word on climate, the 2007 Intergovernmental Panel for Climate Change (IPCC) report. However, the authors were careful not to say how much of this shift in the jet stream was due to natural causes versus human-caused climate change. It is unknown if the jet stream has natural decades-long changes in its path that could account for the observed poleward shift.


Figure 1. The jet stream is located where the strongest winds at the top of the troposphere are found (35,000-45,000 feet high, 200-300 mb in pressure).

Archer and Caldeira note that "These changes in jet stream latitude, altitude, and strength have likely affected, and perhaps will continue to affect, the formation and evolution of storms in the mid-latitudes and of hurricanes in the sub-tropical regions." They don't specify what these changes might be. There is very little research that has been done suggesting how changes in the jet stream might affect hurricane formation and strength. One effect we may begin to see in coming decades is a reduction and/or delay in the number of hurricanes that recurve northward out to sea. Recurvature occurs when a hurricane begins to "feel" the westerly winds of the jet stream. As the jet stream continues to move northward and weaken as the globe warms, we can expect that hurricanes moving though the Caribbean will be less likely to recurve, resulting in more hurricane strikes in Mexico and Central America. Unfortunately, the quality of the Atlantic hurricane database for non-U.S. landfalls is not very good, and it will be several decades before we will be able to tell if the number of hurricane landfalls in Mexico and Central America is increasing due to a poleward shift in the jet stream.

References
Fu, Q., C. M. Johanson, J. M. Wallace, and T. Reichler (2006), Enhanced mid-latitude tropospheric warming in satellite measurements, Science, 312, 1179, doi:10.1126/science.1125566.

Hu, Y., and Q. Fu (2007), Observed poleward expansion of the Hadley circulation since 1979, Atmos. Chem. Phys. Disc., 7, 9367.9384.

Lorenz, D. J., and E. T. DeWeaver (2007), Tropopause height and zonal wind response to global warming in the IPCC scenario integrations, J. Geophys. Res., 112, D10119, doi:10.1029/2006JD008087.

Jeff Masters

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14. Brillig
4:25 PM GMT on June 05, 2008
I think that 5-23 meters should be 5-23 MILES, should it not? I found another reference to the same study that said 12 MILES per decade.

Edit: I see now the article was referring to altitude, not latitude, which was addressed elsewhere in the article.
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13. StormJunkie
4:34 PM GMT on June 05, 2008
10.

Morning KeyWest

There are some nice year to year SST comparison maps here. Although the GOM is not on the same scale as previous years.

You can also find the site those came from and other SST info here. The LSU Wavcis site under marine data is great for GOM info.
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12. ycd0108
4:15 PM GMT on June 05, 2008
Thanks for another interesting post.That topic was the reason I first posted on Wunderground: a friend had asked me to see if there was any such data available. His theory was that global warming could be masked by an equatorward shift and increased wind speed in the Jet Stream. Looks like the opposite is happening.
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11. groundswell
4:30 PM GMT on June 05, 2008
another tidbit of info showing the planet in change mode. There will be the day when all of these contributions to global warming will reach critical mass, and runaway atmosphere change will take place, and we won't be able to stop it. Nope. Too many people in the world.
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10. keywestdingding
4:27 PM GMT on June 05, 2008
sure wish they would fix the sst's on here. especially in the Gulf of Mexico
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9. GainesvilleGator
4:17 PM GMT on June 05, 2008
WPB, that means more hurricanes like Dean & Felix from the Carribean basin.

The USA may get more hurricanes like Katrina, Rita, Jean, & Frances.

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8. StormJunkie
4:22 PM GMT on June 05, 2008
Morning all, interesting read Dr. M.

Good to see ya press
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7. Brillig
4:18 PM GMT on June 05, 2008
The boundaries of the tropics and the artic regions (Tropic of Cancer and Acrtic Circle, for example) are also moving, maybe more than you might think. The Arctic Circle, for example, is moving toward the pole at a rate of about 15 meters per year. This is due to the change in the tilt of the Earth. For some reason, I rarely see this mentioned in discussions of climate change, but I have to believe it's a significant factor.

Edit: Details of these changes are documented at this wikipedia article.
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6. smmcdavid
11:17 AM CDT on June 05, 2008
Good to know... thanks Dr. M.
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5. hondaguy
4:15 PM GMT on June 05, 2008
Interesting read Dr. Masters. I would think that the northern Jet would allow large areas of high pressure (like the Bermuda high) to sit in a position that would curve hurricanes more towards the north/northwestern Gulf Coast unfortunately. I wouldnt think they would curve into Mexico that far west. Unless the storms would break off from the stearing of the high and head towards Mexico/Central America.

I guess that is to be seen though.
4. WPBHurricane05
12:17 PM EDT on June 05, 2008
Does this mean it is going to be warmer and drier in South Florida?
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2. WPBHurricane05
12:14 PM EDT on June 05, 2008
As the jet stream continues to move northward and weaken as the globe warms, we can expect that hurricanes moving though the Caribbean will be less likely to recurve, resulting in more hurricane strikes in Mexico and Central America.

That doesn't sound good.
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1. presslord
12:14 PM EDT on June 05, 2008
Oh boy....
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.