New Study Finds Clouds are Amplifying Human Warming
23
April, 2015
The
mysterious clouds.
For
decades, science has been unable to nail down how clouds might change
with human warming of the climate. Sure, we knew that added water
vapor through a heating-increased amplification of the rate of
evaporation and precipitation would likely impact cloud formation.
But how would those physical alterations impact climate? Would an
added darkening of the Earth through increased cloud cover provide a
cooling effect and slow down the rate of human-caused warming (also
called a negative feedback)? Or would the added water vapor aloft,
itself a powerful greenhouse gas, provide an extra boost to the human
heating engine (also called an amplifying feedback)?
The
mainstream climate models thus assumed a zero to slightly positive
heat feedback from clouds and relied on decadal verification runs to
help test for accuracy. A kind of backwards checking that excluded
values from clouds due to a lack of needed information.
(From
the global climate change perspective, some clouds are worse than
others. The above image shows a thunderstorm set off by massive
wildfires blazing through the permafrost zone near Great Slave Lake
on August 5 of 2014. A pyrocumulonimbus cloud or, colloquially, a
fire thunderstorm. Image source: NASA.)
Confusionists
Take Advantage of Cloud Uncertainty
It
was an uncertainty hanging in the very air above us. An
uncertainty many
climate confusionists used to sow doubt over a broad range of issues
involving how sensitive the Earth is to the human heat forcing.
They often argued, through this scientific dim spot, that climate
sensitivity was, indeed, quite low and that we had very little to be
concerned about regarding an immense dumping of heat trapping gasses
into the atmosphere that is now at least 6 times faster than at any
time in the deep history of life on Earth.
The
shady clouds, in other words, would save us from ourselves.
Not
so fast, said Dr. Andrew Dressler who in
this paper and this
paper recently
defended consensus climate science from the cloudy claims of
confusionists. Dressler, like mainstream climate science, assumed at
least a small degree of positive feedback from changes to clouds and
atmospheric water vapor loading.
And his observational findings were
consistent with an equilibrium climate sensitivity (ECS), or a one
century rate of warming, in the range of 2.0 to 4.5 degrees Celsius
for each doubling of CO2 (consistent with a multi-century warming
[ESS] in the range of 4 to 9 C for each doubling of CO2 — or about
a 6 C average).
New
Study Finds Changes to Clouds are an Amplifying Feedback
But
now, a
new study has found that the picture is not quite so rosy as some
claimed.
The study, led by Dr. Kevin Trenberth, found that net changes to
clouds and related additions of water vapor to the upper atmosphere
is a positive or amplifying feedback to human caused warming. In
other words, the way human heat alters clouds and the related
hydrological cycle results in yet more heat being trapped by the
Earth System.
This
confirms Dr. Dressler’s work and raises a rather unpleasant
question — if we have an added heat feedback from clouds under a
regime of Earth Systems warming, then how strong is it?
What we do find is that if one looks at tropospheric average temperature rather than surface temperature, then there is a much stronger relationship with energy flow at the top of the Earth’s atmosphere. We are able to find a water vapor signal that is clearly a positive feedback.
Climate
Sensitivity Needle May Tilt Toward Upper Range of Estimates
This
is somewhat unhappy news.
What
it means is that the Earth System is at least as sensitive as climate
models suggest. But, even worse, there is a chance that the Earth
System may be closer to the upper range of climate sensitivity
estimates. It means that accumulation of heat in the atmosphere, in
glaciers and in the ocean may happen somewhat faster than consensus
models predict and that geophysical changes may, consequently, be
greater and more catastrophic.
Whether
model simulation of climate sensitivity will need to be altered has
not, as yet, been determined. The study is now very new and it will
take some time for the more recent data to wash out in the model
projections.
But
what can be plainly stated is that fossil fuel industry funded voices
of false comfort have again been proven dreadfully wrong and that
there is some risk that the situation may be even more dangerous than
current science anticipates. As such, there is absolutely no reason
for further delays in policy action and a very rapid draw-down to
zero human carbon emissions.
Links:
Hat
Tip to TodaysGuestIs
No comments:
Post a Comment
Note: only a member of this blog may post a comment.