NASA satellite data are giving scientists insight into how large-scale deforestation in the Amazon Basin in South America is affecting regional climate. Researchers found during the Amazon dry season last August, there was a distinct pattern of higher rainfall and warmer temperatures over deforested regions. Researchers analyzed multiple years of data from NASA's Tropical Rainfall Measuring Mission (TRMM). They also used data from the Department of Defense Special Sensor Microwave Imager and the National Oceanic and Atmospheric Administration's Geostationary Operational Environmental Satellites. The study appeared in a recent issue of the American Meteorological Society's Journal of Climate. Lead authors, Andrew Negri and Robert Adler, are research meteorologists at NASA's Goddard Space Flight Center (GSFC), Greenbelt, Md. Other authors include Liming Xu, formerly of the University of Arizona, Tucson, and Jason Surratt, North Carolina State University, Raleigh. "In deforested areas, the land heats up faster and reaches a higher temperature, leading to localized upward motions that enhance the formation of clouds and ultimately produce more rainfall," Negri said.

Year-to-year changes in concentration of carbon dioxide and methane, two important greenhouse gases in the atmosphere, can be linked to fire activity associated with the El Nino-La Nina cycle, according to a study conducted by a team of NASA scientists and other researchers. Study results appear in an article in the Jan. 2, 2004, issue of Science. "Many scientists have attributed this atmospheric variability to changes in the balance between plant growth and microbial respiration," said James Randerson of the University of California-Irvine, one of the study's authors. "Our work indicates, however, that the sum of these two processes has a smaller impact on atmospheric carbon dioxide levels than previously believed." The scientists also determined almost all the increased levels of carbon dioxide and methane measured during 1997 and 1998 could be attributed to the worldwide fires at the time, underscoring the impact El Nino has on greenhouse gas emissions. Carbon is stored in vegetation, and when the vegetation burns, the carbon returns to the atmosphere.

Two of the nation's premier atmospheric scientists, after reviewing extensive research by their colleagues, say there is no longer any doubt that human activities are having measurable--and increasing--impacts on global climate. Their study cites atmospheric observations and multiple computer models to paint a detailed picture of climate changes likely to buffet Earth in coming decades, including rising temperatures and an increase in extreme weather events, such as flooding and drought. The study appeared December 5 in Science as part of the journal's "State of the Planet" series. The coauthors--Thomas Karl, director of NOAA's National Climatic Data Center, and Kevin Trenberth, head of the Climate Analysis Section at the National Center for Atmospheric Research (NCAR)--conclude that industrial emissions have been the dominant influence on climate change for the past 50 years, overwhelming natural forces. The most important of these emissions is carbon dioxide, a greenhouse gas that traps solar radiation and warms the planet. "There is no doubt that the composition of the atmosphere is changing because of human activities, and today greenhouse gases are the largest human influence on global climate," they write. "The likely result is more frequent heat waves, droughts, extreme precipitation events, and related impacts, e.g., wildfires, heat stress, vegetation changes, and sea-level rise which will be regionally dependent."

global change research
Increasing Greenhouse Gases Lead to Dramatic Thinning of the Upper Atmosphere
The highest layers of the Earth's atmosphere are cooling and contracting, most likely in response to increasing levels of greenhouse gases, according to a new study by scientists at the Naval Research Laboratory (NRL). This contraction could result in longer orbital lifetimes for both satellites and hazardous space debris. In a paper published February 5 in the Journal of Geophysical Research - Space Physics, John Emmert, Michael Picone, Judith Lean, and Stephen Knowles report that the average density of the thermosphere has decreased by about 10 percent during the past 35 years. The thermosphere is the highest layer in the atmosphere, and begins at an altitude of about 90 kilometers [60 miles].

This decrease in density had been predicted by theoretical simulations of the upper atmosphere's response to increasing carbon dioxide and other greenhouse gases. In the troposphere (the lowest layer of the atmosphere) greenhouse gases trap infrared radiation, causing the well-known "global warming" effect. Higher in the atmosphere, above about 12 kilometers [seven miles], however, these gases actually enhance the ability of the atmosphere to radiate heat out to space, thereby causing a cooling effect. As the amount of carbon dioxide increases, the upper atmosphere becomes cooler and contracts, bringing lower-density gas to lower heights. Consequently, at a given height, the average density will decrease. Because each layer of the atmosphere rests on the layers below it, small changes at lower altitudes become amplified at higher altitudes. The NRL study found that the observed decrease in density depends on height in the same way as predicted by the theoretical simulations, indicating that greenhouse gases are a likely source of the change.

global change research
River Indicates Warmer Climate and Earlier Spring in Central Maine
"Warm" is hardly the first word most of us would think of when contemplating Central Maine's winter weather. Yet, a recent study by scientists at the U.S. Geological Survey (USGS), published in the November issue of the journal Climatic Change, suggests what long-time residents have suspected; winter in Central Maine just isn't quite what it used to be. "We compared long-term records of ice thickness and water flow for the Piscataquis River with air temperature for the surrounding area and found significant trends that are consistent with climate warming and advancing spring," said Thomas Huntington, lead author and hydrologist at the USGS Maine District Office. "During the 20th century, average winter temperatures increased by about 3 degrees Fahrenheit and ice on the Piscataquis River on about February 28 was thinner by an average of 9 inches," said Huntington. Other river-flow, temperature, and biologic data analyzed in this study and in studies completed in 1995-2001 throughout New England also consistently indicate systematic, regional late winter and early spring warming during the past century.

global change research
NCAR Explores Link Between Climate Change and Air Quality
The National Center for Atmospheric Research (NCAR) and other institutions are launching a far-reaching project this month to help the government keep polluted areas in compliance with Clean Air Act standards in the event of rising global temperatures. The three-year project will focus on modeling air quality in the United States in the middle of the 21st century. The National Science Foundation, Environmental Protection Agency, and U.S. Forest Service are funding the project.

As the climate warms, the population increases, and forests and croplands are altered, scientists expect the potential for air pollution in coming decades will change in significant and sometimes subtle ways. Policymakers, already concerned about curbing industrial emissions, also must factor in the possibility of more wildfires and the differing impacts that tree plantations and natural forests have on the formation of pollution. "When conditions are changing, all your strategies have to be adjusted," explains NCAR scientist Alex Guenther, who is part of the research team. "For the government to make sure that air quality doesn't worsen, it needs to take into account changes in temperature and vegetation as well as industrial emissions."