CLOUD

The National Center for Atmospheric Research will fly a C-130 research aircraft over Colorado's Front Range this May and July to measure how much carbon dioxide mountain forests remove from the air as spring turns into summer. NCAR scientists and their university colleagues are developing new methods for assessing carbon uptake over complex terrain on regional scales. Accurate assessments could help show to what extent carbon dioxide storage in Western mountain forests -- potentially important "sink" for the greenhouse gas -- may be slowing down as the ongoing drought affects tree growth. Results will be used in testing computer models of forest ecosystem function. The models will help scientists understand the response of forests to drought, fire, insects, and climate change. International pressure is mounting to limit carbon emissions because of their role in global climate change. Better understanding of natural processes involved in forest-air carbon exchange may lead to more accurate monitoring methods and new ways to enhance carbon uptake. High carbon-emitting nations and industries are interested in devising strategies for meeting quotas and trading carbon credits. ACME (short for the Airborne Carbon in the Mountains Experiment) gives scientists an opportunity to combine airborne data with ground-based measurements for the first time to paint a more accurate picture of carbon exchanges in rolling hills and mountain ranges. Local researchers are especially interested in a side trip to assess forest-air exchange over the 150,000-acre Hayman fire burn area. "Wildfires play a big role in controlling vegetation and carbon exchange in the Rockies," says NCAR scientist Dave Schimel, "but most burn areas are too small to assess from an aircraft. For the first time we have a chance to get airborne measurements of carbon directly over a large, disturbed area." Forest losses during the 2002 wildfire season in Colorado reversed years of carbon uptake. The amount of carbon dioxide released from trees during the fires equaled an entire year's emissions from statewide transportation activities. As the research plane samples air aloft, a dense network of instruments will gather data over a half square mile on Niwot Ridge near Nederland. Perched atop three steel towers provided by NCAR, each between 100 and 200 feet tall, carbon dioxide sensors and sonic anemometers will measure changes in carbon levels and winds high above the tree tops. "Today we usually look for carbon in all the wrong places,” says Schimel, "focusing on where it's easy to measure rather than where fluxes are largest.” Most current studies are in flat areas, but most western forests are in the mountains, he explains. Schimel and colleagues have estimated that 25-50% of U.S. carbon uptake occurs in mountainous terrain. In the northern midlatitudes, significant carbon uptake occurs in forests, which are typically left to grow undisturbed in mountainous regions. Ground-based sensors work well in flat land: there are 200 such sites around the world. But in mountain ranges special conditions, such as turbulent airflow, snow pack, vegetation patterns, and contrasts in sunshine and shade, complicate data gathering. The National Science Foundation, NCAR's primary sponsor and owner of the C-130 aircraft, is funding the project. The universities of Colorado, Florida, and Utah, Colorado State University, and Scripps Institution of Oceanography are participating, along with NCAR. C-130 Flight Schedule and Paths Heading out at sunrise from Jefferson County Airport, the C-130 will travel along a 30-mile arm from Winter Park east to Longmont and around a 71-mile oval loop from Idaho Springs north to Allenspark (see map), carrying a belly full of specialized instruments. The aircraft will retrace the pattern again between 2:00 and 4:00 p.m. the same day, flying as low as 1,000 feet above the ground in some places and rising to 16,500 feet in others. The pilots expect to fly four or five days in May and the same number in July. They will also head south to the Hayman burn area southwest of Denver once in May and once in July. Background: Carbon Emission and Storage Human activities put eight billion tons of carbon into the atmosphere each year--six billion from fossil fuel burning and another two billion from forest destruction. But monitors show only half that much building up in the planet's atmosphere. The other four billion tons are removed each year by growing vegetation and ocean waters. The United States alone is responsible for 20%, over 1.5 billion tons, of the global total carbon output. But U.S. forests may remove as much as a half to a billion tons a year naturally as trees grow back on abandoned farmland, spread over historical grasslands, or grow thick with underbrush protected from wildfires, according to NCAR scientist Britton Stephens. Understanding these removal processes better, along with more accurate monitoring, could lead to new methods for enhancing carbon uptake, he adds.