more doubt about computer climate

More Doubt About Computer Climate Models

It is so easy to tweak the data that goes into a computer climate

model in order to generate the desired results --everyone knows that.

When the currently used models try to predict actual measured

temperatures, they fail; so say the authors of this recent study.

Making predictions of future climate change based on these inadequate

models is not justified, not even close.

Peter

Science News

source:

New Study Increases Concerns About Climate Model Reliability

ScienceDaily (Dec. 12, 2007) -- A new study comparing the composite

output of 22 leading global climate models with actual climate data

finds that the models do an unsatisfactory job of mimicking climate

change in key portions of the atmosphere.

This research, published online in the Royal Meteorological Society's

International Journal of Climatology, raises new concerns about the

reliability of models used to forecast global warming.

"The usual discussion is whether the climate model forecasts of

Earth's climate 100 years or so into the future are realistic," said

the lead author, Dr. David H. Douglass from the University of

Rochester. "Here we have something more fundamental: Can the models

accurately explain the climate from the recent past? "It seems that

the answer is no."

Scientists from Rochester, the University of Alabama in Huntsville

(UAH) and the University of Virginia compared the climate change

"forecasts" from the 22 most widely-cited global circulation models

with tropical temperature data collected by surface, satellite and

balloon sensors. The models predicted that the lower atmosphere should

warm significantly more than it actually did.

"Models are very consistent in forecasting a significant difference

between climate trends at the surface and in the troposphere, the

layer of atmosphere between the surface and the stratosphere," said

Dr. John Christy, director of UAH's Earth System Science Center. "The

models forecast that the troposphere should be warming more than the

surface and that this trend should be especially pronounced in the

tropics.

"When we look at actual climate data, however, we do not see

accelerated warming in the tropical troposphere. Instead, the lower

and middle atmosphere are warming the same or less than the surface.

For those layers of the atmosphere, the warming trend we see in the

tropics is typically less than half of what the models forecast."

The 22 climate models used in this study are the same models used by

the UN Intergovernmental Panel of Climate Change (IPCC), which

recently shared a Nobel Peace Prize with former Vice President Al

Gore.

The atmospheric temperature data were from two versions of data

collected by sensors aboard NOAA satellites since late 1979, plus

several sets of temperature data gathered twice a day at dozens of

points in the tropics by thermometers carried into the atmosphere by

helium balloons. The surface data were from three datasets.

After years of rigorous analysis and testing, the high degree of

agreement between the various atmospheric data sets gives an equally

high level of confidence in the basic accuracy of the climate data.

"The last 25 years constitute a period of more complete and accurate

observations, and more realistic modeling efforts," said Dr. Fred

Singer from the University of Virginia. "Nonetheless, the models are

seen to disagree with the observations. We suggest, therefore, that

projections of future climate based on these models should be viewed

with much caution."

The findings of this study contrast strongly with those of a recent

study that used 19 of the same climate models and similar climate

datasets. That study concluded that any difference between model

forecasts and atmospheric climate data is probably due to errors in

the data.

"The question was, what would the models 'forecast' for upper air

climate change over the past 25 years and how would that forecast

compare to reality?" said Christy. "To answer that we needed climate

model results that matched the actual surface temperature changes

during that same time. If the models got the surface trend right but

the tropospheric trend wrong, then we could pinpoint a potential

problem in the models.

"As it turned out, the average of all of the climate models forecasts

came out almost like the actual surface trend in the tropics. That

meant we could do a very robust test of their reproduction of the

lower atmosphere.

"Instead of averaging the model forecasts to get a result whose

surface trends match reality, the earlier study looked at the widely

scattered range of results from all of the model runs combined. Many

of the models had surface trends that were quite different from the

actual trend," Christy said. "Nonetheless, that study concluded that

since both the surface and upper atmosphere trends were somewhere in

that broad range of model results, any disagreement between the

climate data and the models was probably due to faulty data.

"We think our experiment is more robust and provides more meaningful

results."