C
Captain Compassion
Guest
Cirrus disappearance: Warming might thin heat-trapping clouds
(8/9/2007)
For more information:
Phil Gentry, (256)824-6420
http://www.uah.edu/News/newsread.php?newsID=875
The widely accepted (albeit unproven) theory that manmade global
warming will accelerate itself by creating more heat-trapping clouds
is challenged this month in new research from The University of
Alabama in Huntsville.
Instead of creating more clouds, individual tropical warming cycles
that served as proxies for global warming saw a decrease in the
coverage of heat-trapping cirrus clouds, says Dr. Roy Spencer, a
principal research scientist in UAHuntsville's Earth System Science
Center.
That was not what he expected to find.
"All leading climate models forecast that as the atmosphere warms
there should be an increase in high altitude cirrus clouds, which
would amplify any warming caused by manmade greenhouse gases," he
said. "That amplification is a positive feedback. What we found in
month-to-month fluctuations of the tropical climate system was a
strongly negative feedback. As the tropical atmosphere warms, cirrus
clouds decrease. That allows more infrared heat to escape from the
atmosphere to outer space."
The results of this research were published today in the American
Geophysical Union's "Geophysical Research Letters" on-line edition.
The paper was co-authored by UAHuntsville's Dr. John R. Christy and
Dr. W. Danny Braswell, and Dr. Justin Hnilo of Lawrence Livermore
National Laboratory, Livermore, CA.
"While low clouds have a predominantly cooling effect due to their
shading of sunlight, most cirrus clouds have a net warming effect on
the Earth," Spencer said. With high altitude ice clouds their infrared
heat trapping exceeds their solar shading effect.
In the tropics most cirrus-type clouds flow out of the upper reaches
of thunderstorm clouds. As the Earth's surface warms - due to either
manmade greenhouse gases or natural fluctuations in the climate system
- more water evaporates from the surface. Since more evaporation leads
to more precipitation, most climate researchers expected increased
cirrus cloudiness to follow warming.
"To give an idea of how strong this enhanced cooling mechanism is, if
it was operating on global warming, it would reduce estimates of
future warming by over 75 percent," Spencer said. "The big question
that no one can answer right now is whether this enhanced cooling
mechanism applies to global warming."
The only way to see how these new findings impact global warming
forecasts is to include them in computerized climate models.
"The role of clouds in global warming is widely agreed to be pretty
uncertain," Spencer said. "Right now, all climate models predict that
clouds will amplify warming. I'm betting that if the climate models'
'clouds' were made to behave the way we see these clouds behave in
nature, it would substantially reduce the amount of climate change the
models predict for the coming decades."
The UAHuntsville research team used 30- to 60-day tropical temperature
fluctuations - known as "intraseasonal oscillations" - as proxies for
global warming.
"Fifteen years ago, when we first started monitoring global
temperatures with satellites, we noticed these big temperature
fluctuations in the tropics," Spencer said. "What amounts to a decade
of global warming routinely occurs in just a few weeks in the tropical
atmosphere. Then, as if by flipping a switch, the rapid warming is
replaced by strong cooling. It now looks like the change in cirrus
cloud coverage is the major reason for this switch from warming to
cooling."
The team analyzed six years of data from four instruments aboard three
NASA and NOAA satellites. The researchers tracked precipitation
amounts, air and sea surface temperatures, high and low altitude cloud
cover, reflected sunlight, and infrared energy escaping out to space.
When they tracked the daily evolution of a composite of fifteen of the
strongest intraseasonal oscillations they found that although rainfall
and air temperatures would be rising, the amount of infrared energy
being trapped by the cloudy areas would start to decrease rapidly as
the air warmed. This unexpected behavior was traced to the decrease in
cirrus cloud cover.
The new results raise questions about some current theories regarding
precipitation, clouds and the efficiency with which weather systems
convert water vapor into rainfall. These are significant issues in the
global warming debate.
"Global warming theory says warming will generally be accompanied by
more rainfall," Spencer said. "Everyone just assumed that more
rainfall means more high altitude clouds. That would be your first
guess and, since we didn't have any data to suggest otherwise ..."
There are significant gaps in the scientific understanding of
precipitation systems and their interactions with the climate, he
said. "At least 80 percent of the Earth's natural greenhouse effect is
due to water vapor and clouds, and those are largely under the control
of precipitation systems.
"Until we understand how precipitation systems change with warming, I
don't believe we can know how much of our current warming is manmade.
Without that knowledge, we can't predict future climate change with
any degree of certainty."
Spencer and his colleagues expect these new findings to be
controversial.
"I know some climate modelers will say that these results are
interesting but that they probably don't apply to long-term global
warming," he said. "But this represents a fundamental natural cooling
process in the atmosphere. Let's see if climate models can get this
part right before we rely on their long term projections."
--
There may come a time when the CO2 police will wander the earth telling
the poor and the dispossed how many dung chips they can put on their
cook fires. -- Captain Compassion.
Wherever I go it will be well with me, for it was well with me here, not
on account of the place, but of my judgments which I shall carry away
with me, for no one can deprive me of these; on the contrary, they alone
are my property, and cannot be taken away, and to possess them suffices
me wherever I am or whatever I do. -- EPICTETUS
Joseph R. Darancette
daranc@NOSPAMcharter.net
(8/9/2007)
For more information:
Phil Gentry, (256)824-6420
http://www.uah.edu/News/newsread.php?newsID=875
The widely accepted (albeit unproven) theory that manmade global
warming will accelerate itself by creating more heat-trapping clouds
is challenged this month in new research from The University of
Alabama in Huntsville.
Instead of creating more clouds, individual tropical warming cycles
that served as proxies for global warming saw a decrease in the
coverage of heat-trapping cirrus clouds, says Dr. Roy Spencer, a
principal research scientist in UAHuntsville's Earth System Science
Center.
That was not what he expected to find.
"All leading climate models forecast that as the atmosphere warms
there should be an increase in high altitude cirrus clouds, which
would amplify any warming caused by manmade greenhouse gases," he
said. "That amplification is a positive feedback. What we found in
month-to-month fluctuations of the tropical climate system was a
strongly negative feedback. As the tropical atmosphere warms, cirrus
clouds decrease. That allows more infrared heat to escape from the
atmosphere to outer space."
The results of this research were published today in the American
Geophysical Union's "Geophysical Research Letters" on-line edition.
The paper was co-authored by UAHuntsville's Dr. John R. Christy and
Dr. W. Danny Braswell, and Dr. Justin Hnilo of Lawrence Livermore
National Laboratory, Livermore, CA.
"While low clouds have a predominantly cooling effect due to their
shading of sunlight, most cirrus clouds have a net warming effect on
the Earth," Spencer said. With high altitude ice clouds their infrared
heat trapping exceeds their solar shading effect.
In the tropics most cirrus-type clouds flow out of the upper reaches
of thunderstorm clouds. As the Earth's surface warms - due to either
manmade greenhouse gases or natural fluctuations in the climate system
- more water evaporates from the surface. Since more evaporation leads
to more precipitation, most climate researchers expected increased
cirrus cloudiness to follow warming.
"To give an idea of how strong this enhanced cooling mechanism is, if
it was operating on global warming, it would reduce estimates of
future warming by over 75 percent," Spencer said. "The big question
that no one can answer right now is whether this enhanced cooling
mechanism applies to global warming."
The only way to see how these new findings impact global warming
forecasts is to include them in computerized climate models.
"The role of clouds in global warming is widely agreed to be pretty
uncertain," Spencer said. "Right now, all climate models predict that
clouds will amplify warming. I'm betting that if the climate models'
'clouds' were made to behave the way we see these clouds behave in
nature, it would substantially reduce the amount of climate change the
models predict for the coming decades."
The UAHuntsville research team used 30- to 60-day tropical temperature
fluctuations - known as "intraseasonal oscillations" - as proxies for
global warming.
"Fifteen years ago, when we first started monitoring global
temperatures with satellites, we noticed these big temperature
fluctuations in the tropics," Spencer said. "What amounts to a decade
of global warming routinely occurs in just a few weeks in the tropical
atmosphere. Then, as if by flipping a switch, the rapid warming is
replaced by strong cooling. It now looks like the change in cirrus
cloud coverage is the major reason for this switch from warming to
cooling."
The team analyzed six years of data from four instruments aboard three
NASA and NOAA satellites. The researchers tracked precipitation
amounts, air and sea surface temperatures, high and low altitude cloud
cover, reflected sunlight, and infrared energy escaping out to space.
When they tracked the daily evolution of a composite of fifteen of the
strongest intraseasonal oscillations they found that although rainfall
and air temperatures would be rising, the amount of infrared energy
being trapped by the cloudy areas would start to decrease rapidly as
the air warmed. This unexpected behavior was traced to the decrease in
cirrus cloud cover.
The new results raise questions about some current theories regarding
precipitation, clouds and the efficiency with which weather systems
convert water vapor into rainfall. These are significant issues in the
global warming debate.
"Global warming theory says warming will generally be accompanied by
more rainfall," Spencer said. "Everyone just assumed that more
rainfall means more high altitude clouds. That would be your first
guess and, since we didn't have any data to suggest otherwise ..."
There are significant gaps in the scientific understanding of
precipitation systems and their interactions with the climate, he
said. "At least 80 percent of the Earth's natural greenhouse effect is
due to water vapor and clouds, and those are largely under the control
of precipitation systems.
"Until we understand how precipitation systems change with warming, I
don't believe we can know how much of our current warming is manmade.
Without that knowledge, we can't predict future climate change with
any degree of certainty."
Spencer and his colleagues expect these new findings to be
controversial.
"I know some climate modelers will say that these results are
interesting but that they probably don't apply to long-term global
warming," he said. "But this represents a fundamental natural cooling
process in the atmosphere. Let's see if climate models can get this
part right before we rely on their long term projections."
--
There may come a time when the CO2 police will wander the earth telling
the poor and the dispossed how many dung chips they can put on their
cook fires. -- Captain Compassion.
Wherever I go it will be well with me, for it was well with me here, not
on account of the place, but of my judgments which I shall carry away
with me, for no one can deprive me of these; on the contrary, they alone
are my property, and cannot be taken away, and to possess them suffices
me wherever I am or whatever I do. -- EPICTETUS
Joseph R. Darancette
daranc@NOSPAMcharter.net
2qob351498r2ppg16qbmoo5gffuvbpve2@4ax.com...