The jet streams are high-altitude streams of air, about 7 to 16 kilometers over sea level. They blow air from west to east.
Jet streams are important factors in the causation of weather patterns. Therefore, systematic changes in the jet streams are expected to cause changes in weather patterns. Now, we have evidence that the jet streams are changing.
Historical Trends In The Jet Streams
Cristina L. Archer and Ken Caldeira
GEOPHYSICAL RESEARCH LETTERS, VOL. 35, L08803, doi:10.1029/2008GL033614, 2008
published 18 April 2008
Jet streams, the meandering bands of fast winds located near the tropopause, are driving factors for weather in the midlatitudes. This is the first study to analyze historical trends of jet stream properties based on the ERA-40 and the NCEP/NCAR reanalysis datasets for the period 1979 to 2001. We defined jet stream properties based on mass and mass-flux weighted averages. We found that, in general, the jet streams have risen in altitude and moved poleward in both hemispheres. In the northern hemisphere, the jet stream weakened. In the southern hemisphere, the sub-tropical jet weakened, whereas the polar jet strengthened. Exceptions to this general behavior were found locally and seasonally. Further observations and analysis are needed to confidently attribute the causes of these changes to anthropogenic climate change, natural variability, or some combination of the two.
Dr. Cristina Archer is a Research Associate at the Department of Global Ecology, Carnegie Institution for Science, at Stanford. She has degrees in engineering and meteorology. Much of her work has focused on the study of wind patterns, with the goal of optimizing wind power generation.
Dr. Ken Caldeira is a scientist in the same department. (He doesn't have his job title on his website; the department directory lists his as "faculty", and an article in the NYT identifies him simply as "a scientist".) He mostly studies the carbon cycle and geoengineering.
Carnegie has a news page, with a press release pertaining to the study on jet streams:
Changing Jet Streams May Alter Paths of Storms and Hurricanes
Thursday, April 17, 2008
...The observed changes are consistent with numerous other signals of global warming found in previous studies, such as the widening of the tropical belt, the cooling of the stratosphere, and the poleward shift of storm tracks. This is the first study to use observation-based datasets to examine trends in all the jet stream parameters, however.
"At this point we can't say for sure that this is the result of global warming, but I think it is," says Caldeira. "I would bet that the trend in the jet streams' positions will continue. It is something I'd put my money on."
Dr. Archer mentions the disturbing idea that northward movement of the jet streams is likely to increase the frequency and intensity of hurricanes. That's because jet streams tend to inhibit hurricane formation, and they would be less well-positioned to do so, if they move away from the equator.
Like some many climate studies, this one does not prove that climate change is happening in a consistent direction, or that humans are causing it. But it is another bit of evidence that fits in nicely with all (nearly all) the other evidence that we've seen in the past few decades.
Comments
Anytime the jet streams migrate from where we expect to see them, we can presume that there will be a change in the weather patterns and presumably in the climate. Were the jet-streams to move closer to the equator would that be better?
In fact our fragile human infrastructure, in contrast to the robust and enduring ecosystems which are often portrayed as being fragile, are subject to a lot problems no matter how the inevitable shift in our climate comes about. After all, the jet-streams patterns are the result of subtle conditions resulting from everything from ocean currents to the location and heights of mountain ranges as they weather away on the ever-shifting tectonic plates.
Were the jet-streams to just stay where they are forever, would that be better? No doubt it would be for those who think nature is unchanging and for those who fail to see that change is the engine of evolution and diversity and all that we who really love wilderness find so rewarding in nature.
So maybe we should ask: "does the shifting of the jet-stream farther north mean that we'll have cheaper shrimp?"
Posted by: doug l | June 28, 2008 2:25 PM
The point is that we have come to depend upon the weather patterns as they existed in the 20th century. Our ability to protect our houses and other infrastructure, and feed our people, depends upon this pattern. So yes, it would be better if it did not change.
If the jet shreams shifted a hundred miles closer to the poles, we could adapt to that, but it would be costly. If they shift steadily over a period of centuries, that would be a serious problem.
Do I think that nature is unchanging? No. But it is beside the point, for what I think has nothing to do with the question of whether it is a problem.
Posted by: Joseph j7uy5 | June 29, 2008 12:28 PM