U. S. Geological Survey "Global Change" means changes in the global environment

Past and contemporary states and changes in the Earth's environment

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Past and contemporary states and changes in the Earth's environment
It is vital to view possible future climate changes in the context of past climate changes and contemporary climate variation. Knowledge of past climates provides the basis for distinguishing changes caused by human activities from natural climate varia­tion. Information about current Earth systems is equally critical to predicting future changes.
USGS scientists assemble comprehensive pictures of worldwide climates, environments, and ecological systems during specific times in the past using fossils and a variety of other geologic information. Understanding the climates of the past helps us to assess the causes, consequences, and extremes of past climate changes, and thus gain insights into possible future changes. Using climate history, we test the ability of computer models to simulate known climate conditions, thereby improving our abil­ity to model and predict the effects of future global change.
USGS scientists also assemble a variety of data and information about the modern Earth to give us comprehensive pictures of variation and changes in contemporary environmental systems. The combined use of satellite and land-based data describing climate, vegetation, land use, topography, geology, soils, ice, snow, and water allows more accurate representation of terrestrial environmental systems in computer models of global climate.
The USGS studies effects of global change in sensitive environ­ments. For example, ecology, soils, and water resources in arid and semi-arid lands are extremely sensitive to changes in land use, wind, and precipitation. USGS scientists study relations be­tween climate, vegetation, geology, and hydrology to understand causes and effects of climate change in arid lands. They study past episodes of desert formation to understand their causes and effects and to identify areas that are susceptible to desertification.
Many scientists believe that climate changes, and their effects, are more pronounced at high latitudes. Because of this sensitiv­ity, the study of cold regions is important to the early detection of global change. Climate change in cold regions could trigger processes causing further environmental change. For example, arctic envi­ronments are a potential natural source of large volumes of methane. Under warmer conditions or higher sea levels, stored methane could be released, increasing the concentra­tion of greenhouse gases in the atmosphere. The USGS studies methane produced in arctic wetlands and frozen as gas hydrates in permafrost and marine sediments to assist in estimating potential methane release in response to environmental change. The USGS also monitors glaciers and sea ice and studies processes that lead to the advance and retreat of glaciers. It measures temperature profiles in permafrost as a record of recent climate change, and monitors change in permafrost distribution.

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