Clearest Evidence For Human
clouded if more complete data used
More fireworks than usual were detonated on July 4, when Nature magazine published a lengthy article by B.D.
Santer and 12 coauthors that claimed The observed patterns of temperature change in
[the atmosphere away from the earths surface] are similar to those predicted by
state-of-the-art climate models. Newspaper
articles featured Australias Neville Nicholls, one of the lead authors on the new
U.N. report of the Intergovernmental Panel on Climate Change (IPCC), stating this is the
clearest evidence yet that humans may have affected global climate.
There can be little doubt that the
timing of this reportreleased four days before the signatories of the Rio Treaty sit
down to discuss limiting greenhouse emissionswas for maximum political effect. Apparently Nature,
which bills itself as the worlds most prestigious weekly journal of
science is not immune to being toyed with.
More important, though, is the
science. Santers paper correlates
temperature changes predicted by climate models to those observed in the atmosphere above
the surface, as measured by weather balloons. In
general, he found an increasing correlation over time between the models (which include
warming from increasing greenhouse gases and compensatory cooling of sulfate aerosols) and
atmospheric temperatures. There was a slight
additional improvement from inclusion of the effects of stratospheric ozone changes, but
much of which resulted from an idealized altitudinal profile of ozone loss. All in all, its fairest to say that the
best-claimed match-up lies in the sulfate and greenhouse combinations.
Essentially, the models say that
sulfates work to mute warming primarily in the Northern Hemisphere (even creating some
cooling), while the middle atmosphere, from 5,000 to 30,000 feet, warms dramatically in
the sulfate-free Southern Hemisphere.
Santer used two models. One, developed at Lawrence Livermore National
Laboratory (LLNL), has the wrong greenhouse effect. Nowhere
does the paper explicitly state this problem; instead it repeatedly says it is modeling
the atmospheric CO2, which, in fact, underestimates human-caused
changes to the greenhouse effect by almost 50 percent.
The other half (actually 48 percent) comes from non-CO2 greenhouse
enhancers such as methane and CFCs.*
In Figure 1, we adjusted the output
of the LLNL model using the correct greenhouse
forcing. After making standard allowances for
the fact that the earths oceans will retard some of the warming, observed
temperature changes should be around 60 percent of what the map shows. Nonetheless, the overprediction of current
temperature is enormous. While ground-based
records show a warming of about 0.6°C in the last 100 years, this simulation heats up
more than 2°C globallyand the massive warmings of the Southern Ocean and the North
Atlantic, respectively, represent the largest regional errors that we know of.
Figure 1. Temperature change estimated for the Santer et al.
sulfate + greenhouse model when the accepted greenhouse change of 2.45 watts/square meter
is put in the model.
The other sulfate + greenhouse model
that Santer et al. used was published by Mitchell et al. last year and has been repeatedly
cited in this Report because it predicts so
little warming. Because of the sulfates, this
model has just 67 percent of the warming energy of a greenhouse-only model, resulting in a
net warming for a doubling of CO2 of 1.7°C.
But since 0.4°C of this warming has purportedly occurred, this leaves a measly
1.3°C. If the observed change matches up
best with this model, herein lies strong evidence for people who championed the idea that
climate change would be much less than feared.
Ironically, if the full greenhouse
effect changes were incorporated into the model, the correlation between the models and
reality would still increase over time. Thats because of the mathematics involved in
calculating the correlation coefficients that quantify the relative patterns of
temperature change. The global error does
not matter as long as more warming (or less cooling!) is predicted in the Southern
Hemisphere troposphere (lower atmosphere) than in the Northern Hemisphere. Thus, this methodology can take a perfectly absurd
model and still claim that reality increasingly resembles something that
everyoneincluding even the most strident greenhouse alarmistknows to be wrong.
Another reason for the observed
behavior is that much of the correspondence that Santer et al. found between models and
reality is way up in the stratosphere, which has experienced a strong cooling that also
appears in the climate models.
Figure 2 shows their most important
correlation graphs. The chart on the top
shows the increasing correspondence between the LLNL models and the mean temperature
recorded between 5,000 and 65,000 feet. The
one on the bottom is between 18,000 and 65,000 feet.
Figure 2. Correlation pattern changes over time for
5,00065,000 feet (top) and 5,00015,000 feet (bottom). Solid lines are the results for the CO2
only model, while the dotted lines are the results of including the effects of sulfate
aerosols with CO2.
Technically, these are graphs of the
correlation coefficient between the model and observed temperature fields. Squaring the correlation coefficient gives the
percentage of year-to-year variation that is explained, or related, between
the model and reality. In the recent years,
the explained variance between the layer between 5,000 and 18,000 feet is a mere 16
percent (0.4 x 0.4). But when they looked at
the layer between 5,000 and 65,000 feet, the explained variance shoots up to 64 percent
(0.8 x 0.8). Thus, 75 percent of the
correspondence [(64%16%/)/64%] is
because of conformity above 18,000 feet.
Which gets us back to the old problem
that has dogged this issue for decades, namely that greenhouse warming has been very hard
to find in the bottom of the atmosphere, which just happens to be where it matters the
Everyone, from the editor of this Report to Vice President Gore, acknowledges that
the hemispheric mean temperatures measured by satellite correlate perfectly with mean
temperatures measured by weather balloons between 5,000 and 30,000 feet. Because the satellite record shows no warming
since 1979 (near the midpoint of the study period of 1962 to 1987 Santer used), most of
the observed correspondence between the model and reality in recent years must be almost
entirely above 30,000 feet, not just 18,000 feet.
Need proof? Figure 3, taken from Santer et al., shows that the
warming predicted to have occurred in their combined sulfate-greenhouse model is obviously
greatest in the layer that runs roughly from 5,000 to 30,000 feet in the Southern
Hemisphere. Compare this with the
significant decline in the satellite temperatures for that hemisphere as can be found in
our Planet Watch section. Were afraid
that much of the correspondence in Santer et al. stems from the period chosen for study.
Figure 3. Warming predicted in Santer et al., 1996. Hatched areas represent cooling.
We compared Santers results
with the tropospheric and stratospheric temperatures measured by satellites during their
period of overlap. While that period is not
long (eight years), one thing jumped out of our analysis:
The contribution of satellite-measured tropospheric temperature to the
increasing correlation pattern during that period is statistically insignificant. The contribution of stratospheric cooling, which
is forecast by virtually every climate model, was exceedingly important.
Is the Result an
Artifact of the Data Sample?
Much of the increased correlation
between the observed temperatures in the lower atmosphere and the model results from
selection of the weather balloon data. Figure
4 (top), from Santer et al., shows the trend in temperature over the period of his study,
from 1963 to 1987. Note the warming shown in
the Southern Hemisphere around 30° to 60° between 5,000 and 30,000 feet. Weve plotted out the longer temperature
record of 5,000 to 30,000 feet, from Angell et al., which runs from 1957 through 1995, and
included it as Figure 4 (bottom).
Figure 4. Observed warming in Santer et al. (1996) from 1963
to 1987 (top). We have highlighted the region
in the Southern Hemisphere that shows the strong observed warming. The entire temperature history over the same
region from 1957 to 1995 shows no significant warming trend (bottom). However, the period that was chosen for study by
Santer et al. (filled circles) warms dramatically.
The period that Santer et al. studied
corresponds precisely with a profound warming trend in this region. But when all of the data (1957 to 1995) are
included, theres no trend whatsoever! We
dont know what to call this, but we believe that at least one of the 13 prestigious
authors on this paper must have known this to be the case.
The Bottom Line
We are frankly rather amazed that
this paper could have emerged into the refereed literature in its present state; that is
not to say that the work is bad, but that there are serious questionssimilar to
oursthat the reviewers should have asked.
The inescapable conclusions:
1. The vast majority of the
fingerprints of the greenhouse effect are found way up in the atmosphere, especially in the stratosphere.
detection models that were used either dont predict very much future
warming or were run with the wrong greenhouse effect and produce absurd results when the
right numbers are put in.
3. And finally, down here
in the lower atmosphere, the evidence is much more smudged and is based upon a highly
selected set of data that, when viewed in toto,
shows something dramatically different than what the paper purports.
Two weeks ago, in a series of email
exchanges with Dr. Santer, he requested that we print his recent correspondence to the Wall Street Journal, and we agreed to place it in
this issue. We were not informed at the time
of his upcoming Nature article, which we
discuss here. We simply dont have the
space for Santers letter in this issue, but we will print it in the future.
It may have been more appropriate to
delay anyway, as three more letters that relate to this issue appeared in the July 11 Wall Street Journal.
change in warming energy due to the greenhouse effect is 1.26 Watts/square meter in Santer
et al. The IPCC (1995), cited as the
consensus of scientists, gives the figure as 2.45. The atmosphere responds quite linearly to changes
at this level; i.e., 2.45 Watts will produce about 1.9 times as much warming as 1.26
Angell, J.K., (1994
and updates) From Trends 93, U.S.
Department of Energy, 636672.
Nicholls, N., (1996) An Incriminating Fingerprint. Nature 382, 2728.
Santer, B.D. et al.,
(1996) A Search for Human Influences on the
Thermal Structure of the Atmosphere. Nature