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Fall 1999

Science Bits

Data base on reactive chlorine emissions joins GEIA listings

An international team of atmospheric chemists has produced the first gridded global inventory of reactive chlorine emissions to the atmosphere. The research was conducted under the auspices of the International Global Atmospheric Chemistry program's Global Emissions Inventory Activity (GEIA). Results were published this spring in the Journal of Geophysical Research.

"This work provides an objective benchmark for assessing our current understanding of the global chlorine cycle and for investigating the potential environmental implications of future changes in chlorine emissions," said William Keene (University of Virginia), the convener and one of 18 principal investigators for the project. The other PIs were from Dalhousie, Harvard, Portland State, Princeton, Rutgers, and Yale Universities; the Massachusetts Institute of Technology; NCAR; the Universities of Belfast and East Anglia (United Kingdom); and several other agencies and private companies.

Some reactive chlorine compounds contribute to the destruction of stratospheric ozone, some are toxic to humans at high-dose exposures, and others are harmful at chronic, lower-dose exposures.

The project is similar to the global inventory of carbon emissions conducted several years ago to investigate natural and human influences on atmospheric carbon concentrations. That benchmark study was central to the discussions leading to the recent Kyoto protocols, a set of international guidelines for regulating future carbon emissions. "We anticipate that the chlorine emissions study may be employed in a similar manner," Keene said, "although our results are associated with greater uncertainty because multiple compounds are involved and the underlying observational data are more limited."

The chlorine, carbon, and other inventory data may be found at the GEIA Web site. The chlorine inventory was funded by the Chemical Manufacturers Association via the Chlorine Chemistry Council and the European Chemical Industry via Euro Chlor (a federation of the European chlorine industry). Individual investigators also received support from other agencies and institutions, including NSF and the Atmospheric Environment Service, Canada.

University of Virginia


Anthropogenic carbon cost throughout human history

What would the world's forests and natural vegetation be like if humans had never appeared on earth, and how does this compare to what really happened?

In a study presented in August at the meeting of the Ecological Society of America, scientists reported that the amount of vegetation that has been lost to logging, burning, and agriculture throughout human history is the equivalent of about 180 billion tons of carbon. This carbon was transferred to the atmosphere as carbon dioxide.

Since the dawn of the industrial age, fossil fuel use by humans has been the main source of carbon dioxide added to the atmosphere. However, according to Christopher Field, a Carnegie Institution of Washington biologist and coauthor of the study, the net amount of carbon emitted from land-use changes over time is about 75% of the total amount of carbon emitted from fossil fuel burning.

Previous calculations of carbon losses from changes in the earth's vegetation compared conditions in 1850 to those of today. In this study, the first to take into account human land use prior to the mid-1800s, Ruth DeFries, a University of Maryland geographer and lead author of the paper, and Field found that an additional 60 billion tons of carbon was lost before the industrial age. "There has been a huge loss of carbon from the world's ecosystem over the time that humans have been involved in agriculture, and this loss has intensified terrifically in the last few centuries," said Field.

DeFries and Field's study compared NOAA satellite data to an "untouched-by-human-hands" model of the earth's vegetation cover extrapolated from current land-use data. The model looked at areas where forests have been turned into cropland or pasture, where woodlands have been degraded, and where savannas have turned into desert as a result of human activity. "We take into account existing vegetation and compare it to our best guess of what the earth would be like if humans did not disturb the landscape," said DeFries.

Today, the bulk of carbon lost from the earth's vegetation is in the tropics where forests are burned for agricultural purposes. Before 1850, Europe, Asia, and North America were the main carbon sources as massive portions of the forests on these continents were cleared. The largest amount of carbon loss came from Asia with about 70 billion tons. North America, Europe, and Africa lost between 20 and 30 billion tons each since humans began altering the landscape, according to the study.

The study was supported by NASA's Earth Observing System program.

University of Maryland


Secret of coronal heating may be a multitude of tiny blasts

In their quest to find out why the sun's corona is so much hotter than the visible surface, scientists have usually looked at the biggest and brightest events on the surface. Now it appears that the energy source is a continuous rumble of microflares feeding magnetic energy into the corona, heating it to 1 to 2 million Kelvins (1.8-3.6 million °F).

"One microflare has only about 1% of the energy of a large, bright loop," said Ron Moore (NASA Marshall Space Flight Center). "But you have these [relatively] cool microflares constantly going off, and that's enough to heat the corona."

Moore, Jason Porter (NASA Marshall), and David Falconer (University of Alabama at Huntsville) presented their findings at the American Astronomical Society's June conference. They reported on research conducted with the solar vector magnetograph (SVMG), a NASA telescope that reveals the strength and direction of magnetic fields in the solar atmosphere; an X-ray telescope aboard Japan's Yohkoh satellite; and an ultraviolet solar telescope on Europe's Solar and Heliospheric Observatory (SOHO).

Scientists have long puzzled over why the corona has a temperature of 1 to 2 million K when the solar surface only reaches 6,000 K. Since the corona cools rapidly, losing its heat as radiation and the solar wind, something has to be pumping energy upward. But large flare events and bright areas on the surface don't continuously pump enough energy or connect well enough to the corona to sustain the high temperature found throughout the entire corona. For several years, Moore, Porter, and Falconer have believed that the answer was countless microflares, solar flares low in the corona and near the limit of what telescopes can see--that is, about the size of the earth.

Porter overlaid images from Yohkoh's soft X-ray telescope with images from the SVMG, which shows the strength and direction of magnetic fields in the solar surface. He was looking at intense magnetic islands around which large, bright, persistent coronal loops are rooted. The islands are sites of enhanced coronal heating and microflaring.

"A long-term comparison of the hottest emissions from the source regions and the extended loops shows that loops' brightnesses usually do not correspond with the X-ray emissions down at the feet," Porter said. "This implies that the extended loops are heated by some activity that we can't see as hot X-ray microflares."

A new study by Porter, Falconer, and Moore of magnetic islands and extended loops, observed in somewhat cooler radiation (about 1 million K) by SOHO's extreme-ultraviolet imaging telescope (EIT), revealed extreme-ultraviolet microflares that do correlate well with brightening in the extended loops. This indicates that the cooler microflares do drive the heating in the extended loops.

Falconer has added crucial supporting evidence. He took images from the EIT showing the sun in the glow of iron with 11 electrons stripped away (Fe XII). For large regions well away from the strong magnetic fields (the areas around sunspots), Falconer plotted contours between the brightest and darkest spots. The difference between the brightest and darkest areas was only about 50%, no matter when the images were taken.

Studying the dim regions showed that the corona there is rooted in a magnetically controlled network that apparently contributes a significant portion of the coronal heating in these areas, Falconer said. "The bright points--the larger magnetic bipoles in the network--are not a significant contributor to the overall heating of the solar corona. The dominant energy term is in the rest of the network, where the bipoles are smaller and the microflares are too cool to show up as coronal bright points."

To wrap up the study, Moore looked at how much energy comes from microflares around a magnetic island and how much is needed to keep the corona hot in large, bright areas rooted around the island edges. He found that the two balance nicely.

"Each microflare withdraws a small amount from the bank of energy in the sheared region," Moore explained, "so you can have a lot of microflares go off before you deplete your store of energy." By then, more core-field stress generates and the process renews.

University of Alabama at Huntsville, NASA


El Niño, La Niña harming water quality along North Carolina coast

Marine researchers at North Carolina State University say historical data on weather patterns and environmental responses suggest that nutrient loading, algae blooms, and fish kills are closely tied to El Niño and La Niña. Both climate events bring increased amounts of rainfall and high discharge of river water into estuaries on the state's coastal plain.

The team also has identified farming and livestock operations in the middle part of the Neuse River Basin as major sources of nitrogen in estuarine systems tens of miles away on the North Carolina coast. Data analysis shows that nutrient loading is heaviest in the Neuse River's central basin and that nonpoint sources are responsible for the majority of nutrients. These sources can be agricultural, forest, and residential land, whereas point sources include municipal sewage treatment plants and industrial sites.

"We know that El Niño and La Niña control rainfall in North Carolina, Florida, and Louisiana along the Gulf Coast and the southeastern coast," said lead researcher William Showers. "But this is the first time [they have] ever been correlated with water quality events." Showers, doctoral student Jon Karr, and their team presented their findings at the American Geophysical Union's spring meeting.

During El Niño and La Niña events, North Carolina's weather is controlled by storms coming from the Gulf, instead of from the north. The result is warm, wet winters during El Niños and cool, wet springs during La Niñas.

Showers and Karr compared El Niño and La Niña years to river discharge figures in eastern North Carolina and found that both climate modes were correlated with high levels of river discharge. The river waters contain nitrates--nutrient compounds that stimulate algal blooms and can be harmful to fish. The researchers found that high discharge levels were correlated with excess nutrients in the estuaries and fish kill events in the Neuse River Basin. Periods of normal Pacific ocean temperatures--neither El Niño nor La Niña--are correlated to low fish kills.

Showers also pointed to Hurricane Fran as a trigger of more intense nutrient loading on North Carolina's coastal plain. The violent 1996 storm occurred during a year when Pacific conditions were normal. However, "Fran put a tremendous amount of nutrients into the estuary and was associated with a lot of fish kills," he said. "It not only flushed all the groundwater out, but it also washed tremendous amounts of debris from the river basin--downed trees, leaves, and litter--into the river."

Another component of Showers' research is identifying the sources and movements of nutrients in groundwater, surface water, and rainfall using stable isotope technology. "Point sources are responsible for only about 13% of nutrient flux in the [Neuse River] Basin," Showers said. "The urban sources are about 5%. So most of our nutrients are coming from agricultural lands." The likely source is fertilizer or animal waste used on cultivated fields.

Showers said that by using El Niño and La Niña forecasts to predict rainfall and river discharge, we can adjust land-use policies to take better care of our rivers and sounds.

North Carolina State University


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