MYTH #2: 'Recent Global Temperature Rise Has Been
Dramatic.'
THE ENVIROTRUTH:
Dr. Tim Patterson, professor of earth sciences at
Carleton University and others show that in the past
thousand years, there were periods much warmer and
colder than today, long before we began burning
significant quantities of fossil fuels. (An important
March 2003 Harvard University announcement confirms
this). The following graph puts this in perspective
(NOTE: The Sargaso Sea is a two million square mile
ellipse in the North Atlantic that has been studied for
centuries - its temperature variations generally
indicate global trends and agree with the even longer
(6,000 year) Chinese peat bog records.):
Source: Kegwin, L. D. (1996) Science 274, 1504-1508.
From about 900 to 1300 AD, during the Medieval Warm
Period, the Earth was warmer than it is today. In the
20th Century the global average surface temperature rose
about 0.7oC, after a five hundred year cool
period called the Little Ice Age. Only the 20th Century
warming trend may have a human component attributable to
fossil fuel use, which increased sharply after 1940. A
closer look at the 20th century temperature record shows
three distinct trends: First, a warming trend of about
0.5oC began in the late 19th century and
peaked around 1940. Next, temperature decreased from
1940 until the late 1970's - fears of a coming glacial
period dominated during the '70s when Iceland's
fisheries were destroyed by advancing sea ice, winters
in North America were unusually cold and it was first
realized that global temperatures had fallen steadily
between 1940 and 1975. Then a third warming trend
occurred from 1976 to 1986, after which the increase
becomes very small. The largest portion of the warming
for the second half of the 20th century was limited
mainly to winter in the coldest continental air masses
of Siberia and northwestern North America.
So where do environmental groups get the idea that our
planet has warmed dramatically in recent decades? The
answer is simple - they are using the wrong data.
Instead of citing modern, accurate, space-based
measurements, they quote error-prone, ground-based
temperature readings that give little indication of true
global trends.
Until recently the best we could do to estimate the
Earth's overall temperature was to average data
collected at ground stations around the globe. These
readings are notoriously inaccurate as most of them come
from developing countries that do not properly maintain
their stations or records. In addition, there are two
other problems with data collected at the Earth's
surface.
First, nearly all of these stations are land-based, even
though three quarters of our planet is covered with
water. There are far too few temperature-sensing buoys
deployed at sea to give an even remotely accurate
assessment of atmospheric temperature trends in these
vast areas. This is especially significant in the
Southern Hemisphere, which is 90 percent ocean.
Second, urban sprawl has enveloped many temperature
sensing stations in "heat islands" significantly warmer
that the surrounding countryside. The warming measured
at these sites is therefore problematic in determining
global trends.
The only way to properly take the planet's temperature
is to use sophisticated space-based sensors mounted
aboard Earth-orbiting satellites.
Dr. Tim Patterson,
Dr. Pat Michaels, professor of climatology at the
University of Virginia,
Dr. John Christy, Professor and Director, Earth
System Science Center at the University of Alabama,
and many others explain that these far more accurate and
comprehensive satellite temperature sensors reveal a
statistically significant, but very small,
temperature rise since measurements began in 1979. Dr.
Christy says the trend is about 0.07oC per
decade, right at the edge of statistical significance
and certainly far too small to be noticeable.
Here is a temperature plot which show the variation in
temperatures as calculated from satellite measurements:
The following graph, from a somewhat different source, shows the
difference between surface and satellite measurements:
Source: Prepared by John L. Daly (www.john-daly.com)
from raw data from the Earth System Science Laboratory
at the University of Alabama - Huntsville and the GISS.
With the exception of the recent El Niño warming event
(temperatures quickly dropped to normal), both balloon
and satellite data have shown only a minute rise in the
planet's average temperature over the past two decades.
In the final analysis, the Earth is warming ... and it
is getting colder … and it is staying the same. It all
depends on what time frame you are speaking about and
where (and how) you look. |
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