At 09:12 PM 4/18/2006, Craig Rusbult wrote:
> Tonight, "Dimming Sun" was the latest Nova on PBS.
>
> Here is their summary: As global warming
> turns up the heat, researchers are stunned to
> discover that our planet is actually growing
> dimmer. Increasing air pollution allows less
> and less sunlight to reach earth's surface, a
> "global dimming" that's linked to severe
> droughts. In an even more alarming twist,
> there is concern that solving the dimming
> problem could greatly accelerate global
> warming, melting ice caps and flooding coastal cities.
Here is my outline of the show: Actually, the sun
isn't dimming, but particulate pollution is
"blocking" some sunlight, and is also changing
the characteristics of water droplets in clouds
(making them more numerous and smaller, which
reflects sunlight back upward more effectively),
and the overall effect is less solar heating at
the earth's surface, hence "dimming." But
greenhouse gases (CO2,...) are producing a
warming effect. These two effects -- global
dimming and global warming -- are in conflict,
with global warming stronger, on average. Nova
estimated the relative strengths at 2:1, with
half the effects of global warming (2) being
overcome by dimming (1), on average. In the past
few decades, global dimming has been "masking"
the effects of global warming, making us think
the greenhouse effect is weaker than it actually
is. Each effect, dimming and warming, does
unusual things to climate patterns -- changing
the winds, rain patterns,... -- which can upset
things locally. And if we clean up particulate
pollution, global warming won't be masked as
much, and warming will accelerate. As explained
in the PBS summary, "there is concern that
solving the dimming problem could greatly accelerate global warming."
>Interesting.
>
>Craig
@ BS Repellent below. ~ Janice
Welcome to the weblog of the Roger A. Pielke Sr.
Research Group. http://climatesci.atmos.colostate.edu/?p=91
November 27, 2005
<http://climatesci.atmos.colostate.edu/2005/11/27/is-%e2%80%9cglobal-dimming%e2%80%99-really-global/>Is
“Global Dimming” Really Global?
Filed under:
<http://climatesci.atmos.colostate.edu/category/climate-change-forcings/>Climate
Change Forcings Roger Pielke Sr. @ 3:36 pm
The answer according to a new paper is NO.
This paper provides further evidence as to why we
need to focus on local and regional scales if we
are to better understand climate science. The new paper is
Alpert, P. Kishcha, Y. J. Kaufman and R.
Schwarzbard,
<http://www.agu.org/pubs/crossref/2005.../2005GL023320.shtml>“Global
Dimming or Local Dimming? Effect of
Urbanization on Sunlight Availability”
Geophysical Research Letters,32, L17802, doi:10.1029/2005GL023320. 2005.
The abstract of the paper is
From the 1950s to the 1980s, a significant
decrease of surface solar radiation has been
observed at different locations throughout the
world. Here we show that this phenomenon, widely
termed global dimming, is dominated by the large
urban sites. The global-scale analysis of
year-to-year variations of solar radiation fluxes
shows a decline of 0.41 W/m2/yr for highly
populated sites compared to only 0.16 W/m2/yr for
sparsely populated sites (<0.1 million). Since
most of the globe has sparse population, this
suggests that solar dimming is of local or
regional nature. The dimming is sharpest for the
sites at 10°N to 40°N with great industrial
activity. In the equatorial regions even the
opposite trend to dimming is observed for sparsely populated sites.
This paper illustrates the importance of
spatially heterogeneous diabatic heating, as was
discussed, for example, on our weblog of July
28th entitled “What is the Importance to Climate
of Heterogeneous Spatial Trends in Tropospheric
Temperatures?”, and recommended in the 2005
National Research Council report
<http://www.nap.edu/openbook/0309095069/html/>“Radiative
forcing of climate change: Expanding the concept and addressing uncertainties”.
«
<http://climatesci.atmos.colostate.edu/2005/11/26/why-was-my-comment-on-the-david-parker%e2%80%99s-article-in-nature-in-november-18-2005-entitled-%e2%80%9clarge-scale-warming-is-not-urban%e2%80%9d-not-published/>Why
was my Comment on the David Parker’s article in
Nature in November 18 2004 entitled “Large-scale
warming is not urban” not
published?
<http://climatesci.atmos.colostate.edu/2005/12/01/a-new-study-on-the-importance-of-land-surface-types-including-urbanization-on-surface-temperatures/>A
New Study On The Importance of Land-Surface Types
Including Urbanization on Surface Temperatures »
Update April 4 2006
The Climate Science Weblog has clearly documented
the following conclusions since July 2005:
* The needed focus for the study of climate
change and variability is on the regional and
local scales. Global and zonally-averaged climate
metrics would only be important to the extent
that they provide useful information on these space scales.
* Global and zonally-averaged surface
temperature trend assessments, besides having
major difficulties in terms of how this metric is
diagnosed and analyzed, do not provide
significant information on climate change and
variability on the regional and local scales.
* Global warming is not equivalent to climate
change. Significant, societally important climate
change, due to both natural- and human- climate
forcings, can occur without any global warming or cooling.
* The spatial pattern of ocean heat content
change is the appropriate metric to assess
climate system heat changes including global warming.
* In terms of climate change and variability
on the regional and local scale, the IPCC
Reports, the CCSP Report on surface and
tropospheric temperature trends, and the U.S.
National Assessment have overstated the role of
the radiative effect of the anthropogenic
increase of CO2 relative to the role of the
diversity of other human climate climate forcing
on global warming, and more generally, on climate variability and change.
* Global and regional climate models have not
demonstrated skill at predicting climate change
and variability on multi-decadal time scales.
* Attempts to significantly influence
regional and local-scale climate based on
controlling CO2 emissions alone is an inadequate policy for this purpose.
* A vulnerability paradigm, focused on
regional and local societal and environmental
resources of importance, is a more inclusive,
useful, and scientifically robust framework to
interact with policymakers, than is the focus on
global multi-decadal climate predictions which
are downscaled to the regional and local scales.
The vulnerability paradigm permits the evaluation
of the entire spectrum of risks associated with
different social and environmental threats,
including climate variability and change.
Posted November 4, 2005
The Climate Science weblog has been successful in
communicating climate change issues. The comments
have almost always been collegial and
constructive. We will continue to post
information on the weblog that is not readily
accessible elsewhere. The hope is that your views
on climate science are broadened as a result of
reading the weblogs. Please continue to submit comments as appropriate.
Posted July 11, 2005
We are initiating a new blog specifically focused
on climate science issues. Among the topics to be
presented are views on the science that are not
receiving much if any attention in the science
community even though the research is appearing
in the scientific literature. In addition, this
forum provides a venue for the prompt
dissemination of new scientific insight, as well
as issues with balance in the discussion of the
role of human disturbance of the climate system
as reported in national and international assessments, and in published papers.
The views presented in the blog will necessarily
have our perspective. There is an opportunity for
comments to be posted, however, as long as they
are courteous and professionally presented. We
will have the option of not listing these
comments if we find them to not fit this requirement.
Weblog editors:
<mailto:dallas@atmos.colostate.edu>Dallas Staley
and <mailto:tarcieri@atmos.colostate.edu>Tony Arcieri
*
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The final outcome? Estimates of global warming
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Received on Tue Apr 18 21:39:12 2006
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