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February 2008

short takes

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.

hurricane model

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.

volcano

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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