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February 2008
An
overview of projects throughout the organization
Climate
change and ice cream. Vermont-based ice cream
maker Ben & Jerry’s recently calculated
its global warming footprint using a carbon dioxide
emissions scenario developed by Tom Wigley (ESSL/CGD)
in conjunction with colleagues Richard Richels (Electric
Power Research Institute) and James Edmonds (Pacific
Northwest National Laboratory).
Ben & Jerry’s goal was to determine how
much the company must reduce its greenhouse gas emissions
in order to contribute toward reversing Earth’s
warming trend. The emissions target that the company
used, called WRE350, spells out the maximum amount
of carbon dioxide that can be emitted globally over
the next 150 years if humanity wants to stabilize
atmospheric carbon dioxide concentration at 350 parts
per million (ppm). This level is considered by many
scientists to be “safe” in that it would
avoid dangerous human-caused interference with the
climate system. (For comparison, the present-day
level is approximately 385 ppm; the pre-industrial
level measured 280 ppm.)
In consultation with the nonprofit Center for Sustainable
Innovation, Ben & Jerry’s used the WRE350
scenario to calculate the annual level of carbon
emissions that its manufacturing operations can emit
in order to do its share toward reaching the 350
ppm stabilization benchmark. Results indicate that
the company’s plants emitted 6,279 net metric
tons of carbon over the period 2001–2006. This
is 133 metric tons more carbon than its share of
the WRE350 scenario allows, meaning that Ben & Jerry’s
missed its target by the relatively small margin
of 2.2%. According to the company’s Web site,
it plans to make further investments in energy efficiency
to reach the 350 ppm goal.
Boreal
fires and climate. With climate change expected
to increase the frequency and intensity of boreal
wildfires, emissions from these fires are, in turn,
expected to influence climate. But scientists are
unsure about exactly how this will play out. Much
is unknown about the amounts and characteristics
of gases and particles from fires and how they influence
the radiation budget and chemistry of the atmosphere.
A team of scientists from ESSL’s ACD and CGD
recently approached this problem by studying conditions
within the atmosphere and at the very top of it.
They focused on 2000, a quiet fire season, and 2004,
when the fire season in North American boreal forests
was unusually severe. The researchers, led by
ACD’s Gabriele Pfister, integrated satellite
observations and model simulations to look at changes
in both solar radiation and the particle loading
of upper-latitude skies.
They found that the short-term impact of wildfires
may be to cool regional temperatures because a large
fraction (though not all) of the particles in the
smoke block incoming solar radiation. In the long
term, fire emissions appear to warm the climate because
they emit large amounts of carbon dioxide and other
greenhouse gases, which remain in the atmosphere
far longer than the smoke particles. The researchers
also found that the emission inventories and climate
models appear to underestimate both the amount of
particles that are emitted by fires and the extent
to which the particles absorb solar radiation.
The study, which appeared in January in the Journal
of Geophysical Research–Atmospheres, presented
a new way of providing improved estimates for emissions
of particles from wildfires.
Visualizing geoscience. CISL
has released the newest version of VAPOR, an open-source software development
effort to help researchers analyze and interpret results from some of the largest
numerical simulation outputs in the geosciences. Version 1.2.2, released last
month, provides support for the visualization of Weather Research and Forecasting
(WRF) model data sets. This is part of a planned effort over the next year to
broaden VAPOR’s capabilities beyond the needs of physicists investigating
numerically simulated turbulence, instead serving the needs of the more general
Earth and space computational sciences communities.
VAPOR (Visualization and Analysis Platform for Ocean, Atmosphere, and Solar Researchers)
is similar to Google Earth in that both applications employ multi-resolution
data techniques to allow the applications to operate with enormous amounts of
data. Researchers can use VAPOR to explore terascale-size data sets on desktop
computers.
Developed with NSF support by CISL in partnership with the University of California,
Davis, and Ohio State University, VAPOR is quickly gaining recognition throughout
the science community. Researchers have downloaded more than 2,000 copies of
the software, and New Journal of Physics published an invited paper on VAPOR
last year.
More on VAPOR, including a gallery of
visualizations.
Turbulence
in hurricane models. Scientists have discovered
signs of turbulent eddies swirling through a simplified
tropical cyclone. Such turbulence, which occurs on
too small a scale to be directly depicted in global
or regional weather models, was detected by ESSL/MMM’s
Yongsheng Chen and Rich Rotunno in some of the finest-scale
hurricane modeling ever conducted. The two carried
out the initial modeling through a special allocation
of computing power provided late in 2006 with the
arrival of CISL’s Blue Ice supercomputer. Also
contributing were MMM’s Wei Wang, Chris Davis,
Jimy Dudhia, and Greg Holland.
In a hurricane modeled at
185-meter (202-yard) resolution, a smooth ring
of strong wind appears around the eye (left).
When the resolution is increased to 62 meters
(68 yards), the ring breaks into a set of small,
turbulent segments (right). Each image covers
an area of 37x37 km (23x23 miles). (Illustration
courtesy Yongsheng Chen and Rich Rotunno.) |
In a typical hurricane, bands of thunderstorms spiral
into a storm-girdled eyewall, surrounding an eye
that can range in width from less than five to more
than 50 kilometers (3–30 miles). To capture
such features, NCAR in recent years has operated
an Advanced Hurricane WRF (Weather Research and Forecasting)
model with a resolution as high as 1.33 km (0.8 mi).
This model produces realistic-looking spiral bands
that wrap around a distinct eye, much like the pictures
painted by radar and satellite data. However, field
studies show that a great deal of turbulence is hidden
in and near these bands. The bumpy air contributes
to the rough rides often experienced by reconnaissance
aircraft, and it could also influence the larger-scale
evolution of hurricanes.
Yongsheng and Rich set out to see how fine a resolution
would be needed for signs of turbulence to appear
in the model. They found that as the resolution tightens
below 1 km (0.62 mi), the eyewall remains smooth
(see left image), and the peak 1-minute sustained
wind speed increases. However, at the smallest resolution
of 62 meters (68 yards), the eyewall breaks into
short, ragged segments and the peak minute-long wind
actually drops.
Rich speculates that turbulence serves as a brake
on the overall storm intensity. The results,
soon to be published, should help scientists
better assess the factors that determine hurricane
strength in ever-sharpening forecast models.
Injecting sulfates into
the atmosphere mimics a volcanic eruption,
such as this one in northern Chile. When
an eruption has enough force to send fine-grained
particles into the stratosphere, these
particles can linger for several years
and shield enough sunlight to lower global
temperatures measurably. Here, Lascar erupts
in 1993. Although schools as far away as
120 miles (190 kilometers) closed due to
fallout from this eruption, it did not
affect average global temperature significantly.
(Photo by Caspar Ammann.) |
Geoengineering
with sulfate particles. Climate scientists
increasingly have been looking at the plausibility
of “geoengineering” proposals to artificially
cool the planet and mitigate some of the impacts
of climate change. One such plan would be to inject
sulfate particles into the stratosphere, thereby
blocking some solar radiation from reaching Earth’s
surface.
ESSL/CGD’s Phil Rasch recently led a research
effort that used a coupled atmosphere-ocean variant
of the Community Climate System Model to assess the
size and quantity of sulfate aerosols that would
be needed to counteract the warming impacts of increasing
amounts of carbon dioxide in the atmosphere. The
study suggests that annual injections of about 1.5
teragrams (1.7 million short tons) of a sulfur-containing
gas to produce small sulfate aerosols would offset
the warming caused by a doubling of carbon dioxide.
If the sulfate aerosols were large, more would be
needed because larger particles reflect less sunshine
and absorb more infrared radiation.
The research team, which included Danielle Coleman
(CGD) and Paul Crutzen (formerly of NCAR) at the
Max Planck Institute for Chemistry and Scripps Institution
of Oceanography, also found indications that the
geoengineering scenario could have different climatic
impacts in different areas of the globe. Depending
on their size and total mass, the aerosols could
cool the poles more than the equator, influence precipitation
in various regions, or cool the continents more than
the oceans. The planet could also overcool if too
many aerosols were produced in the stratosphere.
The study, published in January in Geophysical Research
Letters, warns that geoengineering by sulfate aerosols
could have other unforeseen environmental impacts
and might affect the ozone layer.
In this issue...
A
closer look at today’s forecast
Internship
programs gear up for summer
The
heart of winter
NCAR/UCAR
media office readies staff for interviews
Short
Takes
Just One Look
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