Back in mid-summer, we reported that
a new independent measure of global temperatures was introduced by a team of investigators
led by Roger Pielke, a Colorado State University atmospheric science professor (WCR,
Vol. 3, No. 21). The new temperatures were derived from pressure readings recorded by
weather balloons. Launched twice a day from a large number of locations worldwide, these
balloons carry an array of meteorological instruments that measure a variety of variables
as they ascend through the atmosphere. These data are relayed back to earth and input into
the computer programs that produce our daily weather forecasts.
Included in each balloons
instrument package is a sensor to measure temperature, and a completely different one to
measure atmospheric pressure.
The weather balloon global
temperature record has been around for years. The temperatures it has recorded in the
lower and middle atmosphere are almost exactly the same as those recorded by satellites
orbiting the earth. During their studys period of overlap (1979 to 1996), these two
records exhibit no discernible warming trend, standing in stark contrast to surface
What Pielke and colleagues did was
derive a new temperature data set from the record of atmospheric pressure readings. How?
Warm air fills more volume than an equal amount of cold air. Therefore, by knowing the
distance between two pressure levels of the atmosphere (a measure of volume), you can
produce a very accurate estimate of the average temperature of the air contained within
The temperatures derived this way are
largely independent from those recorded by the balloons thermometers, and thus
represent a new measure of temperatures in the lower and middle atmosphere.
When analyzing the results from their
new data set, the researchers found that the global averaged temperatures matched up very
well with the global satellite records and showed no warming since 1979 (just like the
balloon thermometer record).
But when we examined the seasonal
behavior of the new data set for each hemisphere, we found some unusual activity. In fact,
we noted in WCR, 3/21 that the seasonal temperature trends reported in the new
Pielke data set for the Northern and Southern Hemispheres were the exact opposite of those
recorded on the surfaceand, for that matter, those found in the satellite
temperature history. The new data showed that the summer months were warming relative to
the winter months. But greenhouse theoryas well as climate projections and observed
datastate that winter warming predominates. So we wondered why it appeared only in
the pressure-based temperatures and not in any of the other temperature histories.
Now we know.
In a newly published
"Correction" to the original article, Pielke and colleagues report that they
mislabeled the hemispheres. Therefore, instead of finding that summers were warming
relative to winters, they find that most of the warming is occurring in winter after all.
(Warmer winters lead to longer
growing seasons, reduced energy costs, and a healthier populace. This is more like what we
expect in a world with an enhanced greenhouse effect.)
This new pressure-based temperature
record is now in line with the other available independent measures of temperatures in the
lower atmospheresatellite-based measurements and weather-balloon thermometer
measurements (Figure 1).
Figure 1. Surface
temperatures (filled circles) seem to be the odd man out. The other three independent
records show no warming.
The discrepancy between surface
temperatures and the other three records remains one of the great mysteries in climate
change science. The lack of press attention to the three unchanging records, however, is
no mystery at all.
Pielke, R.A., Sr.,
et al., Correction to 19731996 trends in depth-averaged tropospheric
temperature. Journal of Geophysical Research, 103, D22, 28,90928,912.
Nightly newscasts have given much
airtime to recent pronouncements that 1998 was not only the warmest global temperature of
the millennium (since thermometers became reliable, circa the mid-1800s), but also the
warmest in the last 600 to 800 years. And of course, humankind is largely to blame.
New research shines some fresh light
on this recent warmth. Judith Lean and David Rind examined the variability of the output
from the sun by analyzing many different sources of data, including historical sunspot
counts, satellite solar radiation measurements, chemical data from tree rings, and even
the variability of other sunlike stars in our galaxy.
Using their best understanding of the
variability of solar output over the past 17 years, they have reconstructed the amount of
solar energy received by the earth for the past 400 years. They found a very strong
correlation between the reconstructed record of global temperatures and their record of
solar output (Figure 1). The more energy the sun emitted, the warmer the earth. The two
records match up very well for the period from about 1610 to 1800. Thereafter, the match,
while still strong, lessens a bit. The authors suggest that this weakening correspondence
between the two data sets exists possibly because something else started to influence
global temperatures around that time. Humans are put forth as one possible cause.
Figure 1. The
reconstructed history of solar output shows that during the 1990s, the sun has shone
brighter than at any time in the last 400 years.
Same-old, same-old? A closer analysis
yields several interesting discoveries. The first is that of the 0.6°C of warming
experienced since the turn of the century, about one-half can be explained by solar
variability. That leaves only about 0.3°C leftover for everything else (rebound from the
Little Ice Age, urbanization, land use changes, etc.). So the climate sensitivity to an
increased greenhouse effect is infinitesimal. Second, reconstructed solar output history
shows that during 1990s, the sun has been shining brighter than at any time in the last
The implication here is that
regardless of human activity, the 1990s would probably have been the warmest decade of the
past 400 years. Add a strong El Niņo into the mix, and voila, you produce the
warmest single year for as far back as records extend.
Weve never heard this
explanation on the evening news.
Lean, J., and D.
Rind, 1998, Climate Forcing by Changing Solar Radiation. Journal of Climate, 11,