[Paleopsych] Fox news distorts global warming reports

[Michael Christopher]

Fox News gets it wrong

Steven Milloy comments on a lecture by Lonnie Thompson
at the Annual meeting of the American Geophysical
Union in San Francisco. He uses a common ploy of
truncating what Thompson said, to ensure that a
quotation fits with his message. According to Milloy,
Thompson said, “Any prudent person would agree that we
don’t yet understand the complexities with the climate
system.” But what he actually said was “Any prudent
person would agree that we don’t yet understand the
complexities with the climate system and, since we
don’t, we should be extremely cautious in how much we
‘tweak’ the system.” (see full press release here).
Such manipulations are designed so that Milloy can’t
be accused of misquoting, but clearly, he completely
contorts Thompson’s point. Milloy also misunderstands
the science.


In his talk, Thompson described two samples of moss
that are 5,000 and 50,000 years old, respectively
(based on radiocarbon dating). These samples have been
revealed as the Quelccaya ice cap in Peru receded over
the last few years. Milloy argues that “the plant find
is a strong indication that, thousands of years ago,
the high Andean climate must have been warm enough to
cause the glacier to be recessed and to allow for the
plants to grow in the first place…”. That is correct.
But he goes on to say, “So if natural forces caused
those climate changes, isn’t it reasonable to conclude
that perhaps natural forces might also be largely
responsible for whatever climate changes may be
occurring now?” Unfortunately, that isn’t reasonable. 

Milloy makes the common mistake of confusing (1)
different factors that cause climates to change (see
forcings) and (2) the rates of climate change. Warming
in the early to mid-Holocene (the post-glacial period
that covers the last 12,500 years) resulted from
changes in the earth’s orbit (as described by
Milankovitch). In the western United States, many
glaciers disappeared altogether at this time, only to
re-form around 4500 years ago. The temperatures slowly
changed as the earth’s position altered, in relation
to the sun, causing the distribution of energy
received on earth to change geographically and
seasonally. The changes observed by Thompson (since he
started studying the Quelccaya ice cap in the late
1970s) have been extremely large and rapid; in fact,
the rate of ice recession has increased over time.
Thompson noted in a 2003 peer-reviewed article, that
“The rate of retreat from 1983 to 1991 was three times
that measured from 1963 to 1983.” (Climatic Change,
vol 59, p.137-159). Evidence of glacier retreat has
been observed in almost all parts of the world in the
20th century, and the rate of retreat has also
increased in the latter half of the 20th century. This
has nothing to do with the slow changes that result
from orbital forcing. It is a consequence of rapid
worldwide global warming, the rate of which has
increased in the last 20 years. As discussed elsewhere
in these pages, there is strong evidence that
anthropogenic effects are largely responsible for this
warming. 

On a more general point, uninformed commentators often
refer to periods in the past when it was warmer, then
claim that this somehow “proves” that contemporary
changes are “normal”. But there were countless warm
periods in the past that resulted from quite different
conditions than those prevailing today (see this link
on the Medieval period, or this link on the
"mid-Holocene" period). In some cases, these were due
to a different orbital configuration, or different
levels of greenhouse gases, or even different world
geography (lower mountain ranges, ocean seaways
altered, no polar ice sheets etc). What makes the
recent changes stand out is that they are extremely
rapid and global in extent. Another error commonly
made is to pick one spot on earth where it may have
been warm, and claim that this demonstrates that the
earth as a whole was warm at that time. This is also
incorrect. If it was warmer in southern Greenland when
the Vikings arrived, this tells us nothing about
conditions in the Pacific, or Eurasia or South
America. To get a true picture of whether there was
“global warming” at that time requires, not
surprisingly, a set of data from many places around
the globe (see this discussion on one of the popular
"myths" regarding past climate history). Thus,
Thompson’s observation about the retreat of the
Quelccaya ice cap would be interesting, but not that
important, if it was the only data point we had. But
it isn’t — we observe similar things happening in
virtually all mountainous regions of the world.

http://www.realclimate.org/index.php?p=85



		
__________________________________ 
Do you Yahoo!? 
The all-new My Yahoo! - What will yours do?
http://my.yahoo.com