Meteorology is outside of my usual topics for posting, but this
particular news item seems to have received little attention elsewhere: there is evidence that the jet streams are moving, systematically,
toward the poles.
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
changes in weather patterns. Now, we have evidence that the
jet streams are changing.
Trends In The Jet Streams
Cristina L. Archer and Ken Caldeira
GEOPHYSICAL RESEARCH LETTERS, VOL. 35, L08803,
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.
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
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:
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
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.