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Balloon Pressure Temps Revisited

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 balloon’s 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 study’s period of overlap (1979 to 1996), these two records exhibit no discernible warming trend, standing in stark contrast to surface measurements.

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 that layer.

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 surface—and, 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 theory—as well as climate projections and observed data—state 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 atmosphere—satellite-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.

Reference:

Pielke, R.A., Sr., et al., Correction to 1973–1996 trends in depth-averaged tropospheric temperature. Journal of Geophysical Research, 103, D22, 28,909–28,912.

 

Warming Up, Naturally

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 400 years!

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.

We’ve never heard this explanation on the evening news.

Reference:

Lean, J., and D. Rind, 1998, Climate Forcing by Changing Solar Radiation. Journal of Climate, 11, 3069–3094.