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E-M:/ Fwd: Shift in Great Lakes seasons may reflect global warming trend

Enviro-Mich message from Kirk Riley <rileyki@egr.msu.edu>

Forward of recent posting to environmental listserv.  The message: the 
Great Lakes seasons--the cycling of water in the lakes--now come a month 
earlier because of climate change, perhaps global warming.


>X-Mailer: Microsoft Outlook Express 5.00.2615.200
>Date:         Wed, 24 May 2000 12:47:11 -0400
>Reply-To: Karen Claxon <kclaxon@earthlink.net>
>Sender: Environmental Discussion List <ENVST-L@LISTSERV.BROWN.EDU>
>From: Karen Claxon <kclaxon@earthlink.net>
>Subject:      GW:  Shift in Great Lakes seasons may reflect global warming 
>: 24 MAY 2000 AT 07:00 ET US
>Contact: John D. Lenters
>University of Wisconsin-Madison
>Shift in Great Lakes 'seasons' may reflect warming trend
>Scrutinizing a 139-year record of Great Lakes water levels, a
>University of Wisconsin-Madison scientist has discovered a dramatic
>shift in the seasonal changes in water levels on the Great Lakes.
>The finding, reported here today, May 24, at a meeting of the
>International Association of Great Lakes Research by UW-Madison
>climatologist John D. Lenters, is further evidence that the effects
>of global warming on natural systems could be far reaching and
>"The bottom line is that over this 139-year period, the annual rising
>and falling of Lakes Ontario and Erie has gotten earlier" by about a
>month, Lenters says describing results of an analysis of long-term
>trends in Great Lakes water levels.
>The findings, Lenters says, also show that the range of Lake
>Ontario's "annual cycle" increased from 17 to 22 inches, a change in
>volume equivalent to 90 billion cubic feet of water. While Lake Erie
>does not show the same increase, the one month early arrival of
>seasonal high and low water levels mirrors that of Lake Ontario.
>In the Great Lakes, explained Lenters, there is an annual ebb and
>flow of lake levels influenced by such things as precipitation,
>snowmelt and evaporation over the Great Lakes basin. In the spring
>and summer, lake levels rise reflecting such things as precipitation
>and spring snowmelt. In the fall and winter, lake levels recede as a
>result of evaporation of the relatively warm lake water.
>These shifts, says Lenters, are essentially hydrological
>representations of the seasons, and "what I am finding is a shifting
>of the seasons."
>These shifts are independent, Lenters says, of annual variability in
>lake levels that may reflect, for example, a drought year, or a year
>when rainfall exceeds normal precipitation averages.
>"At this time, the most likely explanation for the observed trends
>appears to be earlier spring snowmelt in association with higher
>springtime temperatures in the Great Lakes region," Lenters says.
>"Climate is almost definitely responsible, but exactly how it is
>responsible is unknown."
>Lenters' analysis was made using records of monthly mean lake levels
>from 1860 to 1998 from four stations around the Great Lakes,
>including stations along Lakes Superior, Huron, Ontario and Erie.
>Lake Michigan is included in the study as part of Lake Huron since
>the two lakes are hydraulically connected.
>Large shifts in the water cycles of Lakes Superior and Michigan-Huron
>were also found, but for fewer months of the year. The result is a
>different and less dramatic seasonal shift for those lakes, says
>"It is not clear why Lakes Superior and Michigan-Huron are behaving
>differently, but it may be related to differences in regional
>climate, or the fact that Erie and Ontario are the furthest
>downstream lakes.
>"If warming continues, we may begin to see the same consequences in
>Lakes Superior, Michigan and Huron," he says. "For example, following
>the warm El Niņo winter of 1997-1998, all five Great Lakes reached
>their annual maximum nearly two months earlier than normal."
>It is likely that the changes observed in the lakes are part of a
>larger systemic change spurred by increased levels of carbon dioxide
>in the atmosphere and resulting warming trends, according to the
>Wisconsin climatologist. Similar long-term shifts in lake ice and
>river flow in the Great Lakes and Upper Mississippi basins have
>already been observed by scientists.
>Terry Devitt
>Lenters is a staff scientist in the Climate, People and Environment
>Program of the UW-Madison Institute for Environmental Studies. His
>work was supported by a grant from NASA's Upper Midwest Regional
>Earth Science Application Center.
>Note: Until June 6, messages for Lenters can be left at the following
>number: 608-278-1680. He will be checking messages several times a

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