alt.energy.renewable

"Ouroboros_Rex" wrote
> Water vapor is not increasing.

Actually it is.

Increase In Atmospheric Moisture Tied To Human Activities
by Staff Writers
Livermore CA (SPX) Sep 19, 2007

Observations and climate model results confirm that human-induced warming of
the planet is having a pronounced effect on the atmosphere's total moisture
content. Those are the findings of a new study appearing in the Sept. 17
online edition of the Proceedings of the National Academy of Sciences. "When
you heat the planet, you increase the ability of the atmosphere to hold
moisture," said Benjamin Santer, lead author from Lawrence Livermore
National Laboratory's Program for Climate Modeling and Intercomparison.
"The atmosphere's water vapor content has increased by about 0.41 kilograms
per cubic meter (kg/m²) per decade since 1988, and natural variability in
climate just can't explain this moisture change. The most plausible
explanation is that it's due to the human-caused increase in greenhouse
gases."

More water vapor - which is itself a greenhouse gas - amplifies the warming
effect of increased atmospheric levels of carbon dioxide. This is what
scientists call a "positive feedback."

Using 22 different computer models of the climate system and measurements
from the satellite-based Special Sensor Microwave Imager (SSM/I),
atmospheric scientists from LLNL and eight other international research
centers have shown that the recent increase in moisture content over the
bulk of the world's oceans is not due to solar forcing or gradual recovery
from the 1991 eruption of Mount Pinatubo. The primary driver of this
'atmospheric moistening' is the increase in carbon dioxide caused by the
burning of fossil fuels.

"This is the first identification of a human fingerprint on the amount of
water vapor in the atmosphere," Santer said.

"Fingerprint" studies seek to identify the causes of recent climate change
and involve rigorous comparisons of modeled and observed climate change
patterns. To date, most fingerprint studies have focused on temperature
changes at the Earth's surface, in the free atmosphere, or in the oceans, or
have considered variables whose behavior is directly related to changes in
atmospheric temperature.

The water vapor feedback mechanism works in the following way: as the
atmosphere warms due to human-caused increases in carbon dioxide, methane,
nitrous oxide, and chlorofluorocarbons, water vapor increases, trapping more
heat in the atmosphere, which in turn causes a further increase in water
vapor.

Basic theory, observations and climate model results all show that the
increase in water vapor is roughly 6 percent to 7.5 percent per degree
Celsius warming of the lower atmosphere.

The authors note that their findings, when taken together with similar
studies of continental-scale river runoff, zonal-mean rainfall, and surface
specific humidity, point toward an emerging human-caused signal in the
cycling of moisture between the atmosphere, land and ocean.

"This new work shows that the climate system is telling us a consistent
story," Santer said. "The observed changes in temperature, moisture, and
atmospheric circulation fit together in an internally- and
physically-consistent way."

Q1: What is the scientific focus of our PNAS paper"

Our paper looks at the causes of changes in the moisture content of Earth's
atmosphere. Since the start of routine satellite-based measurements of
atmospheric water vapor in September 1987, atmospheric moisture content has
increased markedly. This increase had been noted in previous scientific
papers, and was prominently mentioned in the IPCC's Fourth Assessment
Report. But the causes of the increase were not known. Our investigation was
the first to use rigorous statistical "fingerprint" methods to tackle the
question of why water vapor has increased.

Q2: What is climate "fingerprinting""

Basically, "fingerprinting" involves searching for a computer
model-predicted pattern of climate change (the "fingerprint") in observed
climate records. Fingerprint techniques allow researchers to examine a
change in some property of the climate system and make rigorous statistical
tests of the different possible explanations for that change.

Q3: What were the primary findings of our study?

Our key findings were as follows:

Despite the relatively short length (19 years) of the observed water vapor
data, we were able to identify a "fingerprint" of human activities in this
observational record.

Unlike most previous "fingerprint" work, our study used results from
virtually all of the world's major climate models. We showed that our
identification of a human "fingerprint" in satellite-based water vapor
records was robust to current uncertainties in climate models.

The model results enabled us to "disentangle" the contributions of different
factors to the overall increase in water vapor. We found that in climate
models, this increase in water vapor was primarily due to human-caused
increases in greenhouse gases.

Bottom line: our results suggest that there is an emerging signal of human
activities in the moisture content of Earth's atmosphere. The climate system
is telling us a consistent story. The observed changes in temperature,
moisture, and atmospheric circulation fit together in an internally- and
physically consistent way.

Q4: Does our work have any larger implications"

Yes

One persistent criticism of the "discernible human influence" findings of
previous IPCC assessments is that such conclusions were largely based on
"fingerprint" studies which relied heavily on surface temperature changes.
The thrust of the criticism was this:

"If there really is a signal of human activities lurking in the climate
system, it should be manifest in many different climate variables, and not
in surface temperature alone".

Our study helps to refute this criticism, and shows that we have now moved
well beyond "temperature only" fingerprint studies.

Q5: Why should we care about the behavior of water vapor"

There are at least three reasons why we should pay attention to water vapor.
First, water vapor is itself a potent greenhouse gas, so it is important to
have a good understanding of the cause or causes of its recent increase.
Second, atmospheric moisture content is one of the large-scale environmental
conditions that influences the genesis and development of hurricanes. In the
absence of countervailing changes in other factors, an increase in water
vapor would favor the development of more intense hurricanes. Finally, the
observed increase in water vapor provides independent evidence of the
reality of warming of the lower atmosphere. The observed water vapor
increase since 1988 is consistent with pronounced warming of the surface and
lower atmosphere, but fundamentally inconsistent with claims (still made by
some die-hard skeptics!) that the lower atmosphere has cooled over recent
decades.

The Livermore authors included Karl Taylor, Peter Gleckler, Jim Boyle and
Stephen Klein. Other scientists contributing to this research were Carl
Mears and Frank Wentz at Remote Sensing Systems in Santa Rosa, Calif.; Tom
Wigley, Jerry Meehl, and Warren Washington at the National Center for
Atmospheric Research in Boulder; Tim Barnett and Dave Pierce at Scripps
Institution of Oceanography in La Jolla; Wolfgang Bruggemann at the
University of Hamburg in Germany; Nathan Gillett at the University of East
Anglia and Peter Stott at the Hadley Centre for Climate Prediction and
Research (both in the U.K.); Toru Nozawa at the National Institute for
Environmental Studies in Japan; and Mike Wehner at Lawrence Berkeley
National Laboratory.