National center for Atmospheric Research NcAR

BASED IN boulder, Colorado, the National Center for Atmospheric Research (NCAR) provides the university community with the tools, facilities, and support required to perform innovate research. Through NCAR, scientists have access to high-performance computational and observational facilities, such as supercomputers, aircraft, and radar. These resources can be used to improve human understanding of atmospheric and Earth system processes. NCAR and university scientists collaborate on issues such as atmospheric chemistry, climate, cloud physics and storms, weather hazards to aviation, and interactions between the Sun and Earth. In all of these areas, scientists are looking closely at the role of humans in both creating climate change and responding to severe weather occurrences.

The core research of NCAR is based on the assumption that human activities are causing large-scale changes in the Earth system. The advances in scientific understanding, Earth system modeling, and computational and observational technology can shed new light on how the Earth system works. NCAR's activities contribute to the development of a predictive Earth system science that can help sustain Earth's habitabil-ity, improve environmental quality, safeguard human health, reduce the impacts of natural disasters, and increase economic productivity. This predictive Earth system becomes of particular importance in the face of global warming. The Climate and Global Dynamics Division of the Earth and Sun Systems Laboratory conducts broad-ranging research on all aspects of climate. The center explicitly connects global climate change, "whether it involves more heat or more cold, more precipitation or more drought," with "planetary warming." NCAR estimates that, since 1900, the Earth has warmed about 1 degrees F (about 0.6 degrees C). This warming of temperatures has various effects regionally. The center points out that scientists contributing to the 2007 International Panel on Climate Change predict changing precipitation patterns and retreating glaciers in Latin America, higher crop productivity in high-latitude regions, and sea-level rise along coastal regions. To lessen the insecurities about future climates, NCAR employs various tools and techniques, including climate models, radar and weather-balloon observations, satellite data, and so on, to understand the impacts of global and regional climate change.

NCAR has taken a clear stance on global warming, arguing that the data collected for more than 100 years on the Earth's surface temperature through a global network of land-based weather stations, supplemented by readings taken across the oceans, have shown a global rise in temperatures since the late 1800s. The center identifies human activities that amplify the natural greenhouse effect as "a major culprit." The NACR report on the topic states that "this warming of the average temperature around the globe has been especially sharp since the 1970s." The global models at NCAR have simulated 20th century climate and found three main factors at work. Solar activity contributed to a warming tendency in global average temperature in the first three decades of the last century. However, climate simulations at NCAR have shown that solar changes are accountable for less than a third of the warm-up during the last century. As industrial activity increased after World War II, Sun-blocking sulfates and other aerosol emissions helped lead to a slight global cooling up until the 1970s. Since 1980, the rise in greenhouse gas emissions from human activity has overwhelmed the aerosol effect to produce overall global warming. Thus, the most straightforward explanation for a warming Earth, NCAR states, is the greenhouse gases emitted when fossil fuels are burned in homes, gas and coal-fired power plants, vehicles, and factories. One of the objections of global warming skeptics is that some urban areas warm up due to the heat-island effect, because buildings and pavement retain more heat than undeveloped areas. NCAR scientists and researchers have made their estimates on global warming with particular attention to this heat-island effect. They have worked to remove and other potential biases from the global record. Even after these adjustments, they claim that the rise in global temperature remains clear.

NCAR lists other signs of a warming planet, such as retreating glaciers. Modeling by NCAR scientists has shown that, in the Arctic, the thickness and extent of summer sea-ice have decreased at a fast pace over the last 50 years. In addition, NCAR modeling has predicted that the Arctic's summer ice may virtually disappear by 2040. The increasing snowfall over Antarctica is, to NCAR scientists, a paradoxical sign of warming temperatures in this frozen land. The annual cycle of plants and migrating animals points to a expansion of the warm season over much of the Northern Hemisphere.

Reporting on the temperature in the troposphere several miles above Earth, NCAR states that satellites initially showed a smaller temperature rise at these heights than at ground level. Yet, it now seems that most of the disagreement was due to errors in the satellite data and how they was interpreted. There are still differences between tropospheric and surface warming in some regions, but NCAR researchers point out that a 2006 U.S. Climate Change Program report has cancelled the discrepancy on a global scale. NCAR is committed to the improvement of data-gathering, computer modeling, and analysis for studies of past, present, and future climate. For example, research at NCAR has focused on a re-examination of the role of decades-long cycles of solar variation in explaining the observed warming in the first half of the 20th century. NCAR researchers have identified another impact of humanity's increasing consumption of fossil fuels: the alterations in seawater chemistry as the oceans absorb more carbon dioxide. These alterations create a real danger to marine organisms, including those that build coral reefs around the world.

Many NCAR scientists are part of a global team studying global warming and its meaning for the Earth's future. In 2001, NCAR scientists estimated that increasing levels of greenhouse gases will warm the globe by a significant amount. They came up with a 90 percent likelihood that the range will fall between 3 and 9 degrees F (1.7-4.9 degrees C) over 1990 levels by the year 2100. NCAR researchers have concluded that the effects will be far more varied than a simple, uniform warming over the entire planet, because heating also alters the water cycle, among other changes. As a result, some regions will become con siderably hotter or cooler, or wetter or drier, than others. NCAR scientists are working to improve understanding of potential regional changes in climate, such as the change in U.S. rainfall and snowfall patterns. Researchers are also working to translate temperature changes from a model into consequences that affect people's everyday lives. A 2004 NCAR study estimated that, by the period 2080-99, American and European heat waves will be more severe, frequent, and will last longer. A related study found that days in which temperatures dip to 32 degrees F (0 degrees C) will decrease in many parts of the globe by 2080-99. The biggest reductions are foreseen for the northwest parts of Europe and North America.

New research, in 2006, by NCAR scientists considered more specifically the possibility of an increase in weather extremes in a warmed climate. Employing simulations from nine different climate models, the researchers demonstrated the risk of dangerous heat waves, intense rains, and other kinds of extreme weather in the next century. NCAR studies have been used in preparing the 2007 Intergovernmental Panel on Climate Change assessment.

SEE also: Bush (George W.) Administration; Climate.

bibliography. Thomas R. Karl, et al., Temperature Trends in the Lower Atmosphere: Steps for Understanding and Reconciling Differences, www.climatescience.gov/Library/sap/sap1-1/finalreport/default.htm; National Center for Atmospheric Research, www.ncar.ucar.edu (cited November 2007).

Luca Prono University of Nottingham

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