Ask A Scientist Weather Archive

name         Brian F.
status       other
age          30s

Question -   I have heard that rising global temperatures and the ensuing melting of the 
polar ice caps have dropped the temperatures of the major oceans.  This in turn has 
effected the process of convection which creates and controls weather patterns.  So, 
say, if the pacific current is weakened, will the jet stream be likewise effected?  Will 
the arctic stream be stronger?  Will the overall temperatures in North America actually 
drop as the rest of the planet gets warmer?
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Dear Brian-

Those are all good questions...and lots of scientists and researchers are working hard to find 
the answers.  There are many theories concerning the origin or cause of global warming, none of 
which have been proven conclusively.  The earth has undergone periods of warming and cooling 
many times in the thousands and millions of years before this current period.  There is not 
even consensus as to whether the current observed warming is from natural causes or from 
human activity.  Various sophisticated computer models can predict possible effects from 
various amounts of warming, but these again depend on lots of variables that may interact 
in ways we do not understand.

There is lots of information concerning global warming on the Internet.  Go to www.google.com 
and do a search on "global warming," and you will receive more than a million links.  
Just remember that most of what is said or written is speculation based on certain assumptions 
and incomplete data.  We need many more years of observation and research before we can even
precisely define the problem.

Wendell Bechtold, meteorologist
Forecaster, National Weather Service
Weather Forecast Office, St. Louis, MO
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Brian,

You have asked some complex questions.

First, remember that the jet streams are strongest over land areas, where the north-south 
temperature gradients are much larger than over the oceans.  Certainly, global warming would be 
likely to change ocean and atmospheric circulations to some degree, although it is still not clear 
exactly how or to what degree.  To the degree that the circulations might be affected, the jets 
would probably  be affected as well, although to what extent is not clear yet.

Global warming, if it is indeed occurring, has been slight so far. I say "if it is indeed 
occurring", because the ability to measure
surface and upper atmospheric temperatures over the past hundred years or so and our understanding 
of how to average the temperatures from measurement stations over that period is still debated and 
being investigated. A slight warming trend appears
to have occurred over the past 100 years, although most of that has occurred since World War II and 
especially since the early 1980s.  Whether this has been caused by man or is part of a natural 
cycle (or perhaps both) remains to be shown.

Recent data suggest that the polar ice has not decreased as at first thought, but, for the North 
pole in particular, may have slightly thinned due to a natural cycle.  This requires more study.  
The ice cap on Greenland has not changed in total amount, but in extent, having increased in 
thickness in the central part of the island while decreasing in depth near the coast.  Some 
glaciers are decreasing in some areas of the world, but are increasing in others.  There is a 
lot of seemingly contradictory information that has yet to be sorted out in the global climate 
change picture.

The ocean temperature has not appreciably changed recently, according to the most recent 
information that I have read. If the polar ice did decrease, it is unlikely to directly cool 
the oceans on average, as energy input from the warmer atmosphere would probably make up the 
difference.  Therefore the northern hemisphere surface temperature (most of which is isolated 
from the affects of the oceans) would increase, despite any melt from the ice cap.

Convection occurs mostly over land surfaces and would likely be enhanced if surface temperatures 
increased.  This might then lead to more evaporation, precipitation, and thus a reduction in the 
effects of warming.  The atmosphere has significant feedback mechanisms that attempt very strongly 
to maintain the atmospheric status quo.

A major concern, should the polar ice melt significantly, is the affect on the oceanic circulation 
in the North Sea of the  Atlantic.  A significant change in this circulation could in turn affect 
the Gulf Stream circulation, thereby upsetting a large climatological region of the world.  It has 
been theorized, through computer modeling, that this may have happened in the past, thereby 
contributing to some of the large climate shifts that seem to be detectable in the climate 
record deduced from ice cores and ocean sediments.

David R. Cook
Atmospheric Research Section
Environmental Research Division
Argonne National Laboratory
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