Scientists worldwide are taking the earth's temperature. For two decades, engineering students in the Thermal Radiation Group at Virginia Tech have been testing and improving the instruments carried by NASA satellites to provide data to atmospheric scientists.
The earth's climate is driven by absorbing solar energy and radiating thermal energy back to space. Do man-made gases and particles interfere in the earth's atmosphere and have a cooling effect or a heating effect? Are we headed for the big chill or global warming?
Man-made and natural gases and particles have both a cooling and a heating effect. For example, in the upper atmosphere, chlorine can destroy ozone, which protects the earth from ultraviolet radiation. At lower levels, ozone is a major component of smog and is a greenhouse gas.
Global warming? Some gases, such as water vapor, carbon dioxide, methane, and CFCs, are largely transparent to incoming radiation from the sun but trap outgoing infrared radiation, like glass traps air in a greenhouse, and thus heat the surface. Is that bad? Without the greenhouse gases, the earth's surface would be about minus 2 degrees F. For the past 200 years, however, atmospheric carbon dioxide has increased rapidly due to fossil-fuel burning and deforestation, and early climatic models predicted significant global warming. But warming appears to be less than anticipated.
Cooling? Carbon dioxide emissions and fossil fuel combustion release sulfur dioxide, which is oxidized in the atmosphere to sulfuric acid, known to form particles that make up clouds. These particles scatter incoming solar radiation back into space, causing a cooling effect. Dust, salt from sea spray, and other natural aerosols also scatter radiation and create a layer that prevents energy from escaping.
What is the balance?
"It's difficult to know which effect is bigger," says Cristina Sanchez, master's candidate in mechanical engineering at Virginia Tech. "The data are so new. Continuous, long-term results from the satellites only began to come in 10 years ago."
Sanchez, who is from Bogota, Colombia, is part of the Thermal Radiation Group that is modeling and designing instruments that measure energy radiated and reflected from the earth Ñ the earth's radiation budget.
The Thermal Radiation Group creates and applies software and computer models to test the designs of instruments carried by NASA satellites as a part of the Mission to Planet Earth, a multibillion dollar international science program. A community of scientists is using space- and ground-based measuring systems to study the earth's climate. NASA has placed three satellites in orbit since 1979 for continuous, long-term observation of the radiative components of the climate system and is now providing scientists with a 15-year record of a large number of atmosphere processes.
With these instruments, scientists can determine how much energy is reflected or released. The balance is the amount trapped. Determining the balance helps them determine whether it is getting hotter or colder.
Katherine Coffey, master's student from Virginia, explains, "Scientists are using the data to model the earth as a system." They want to be able to predict what global climate changes result from various actions accurately enough to help people in government and industry make decisions that will protect the environment and human health.
Currently, the Earth Radiation Budget Experiment (ERBE) satellites carry detectors that were modeled and improved by members of the Thermal Radiation Group. As a result of data from ERBE, scientists decided the next satellites need improved measurement of radiation from clouds and the cooling effect on the earth. Thus NASA satellites in the Clouds and Earth's Radiative Energy System (CERES) program will enhance data collection by focusing on clouds.
CERES instruments combine the input from various measurement systems Ñ optical, thermal-radiative, and electrothermal Ñ to reduce gaps and errors in data collected. Kory Priestley, a doctoral graduate of the Virginia Tech group, developed a mathematical model of the CERES instruments' process for converting radiation into electrical signals and is using it at NASA to test data interpretations.
On campus, Sanchez is analyzing the cavity of the measurement device, where the sensors are located. Master's student Stephanie Weckmann, who is from Marseille, France, is analyzing the sensors themselves.
Doctoral student Felix Nevarez of San Juan, Puerto Rico, is developing software that will allow the analysis of any sized cavity by simply entering information about the cavity, rather than having to write a new program for every change in a cavity's dimensions.
"Creating a prototype is costly, so you model first," explains Coffey. "When you are confident that a device will work from your models, then you build the prototype."
Although Mission to Planet Earth hasn't answered all the questions, scientists have been able to make recommendations and people have begun to respond to the decades of climate study. The United States has banned the use of freon, for example. Researchers from many nations are working to help people make a living from rain forests without destroying them. Nations from around the world are investing in the effort, sharing results, and debating how to respond.
Internet sites: Earth Observing System; Smoke, Clouds, and Radiation article; NASA; Mission to Planet Earth; Dissertations by Martial Haeffelin and Rahul Zaveri
— Written by Susan Trulove