Expected Effects in the U.S.
Temperature and Precipitation Projections
Global average temperatures are projected to rise over this century. Temperature increases will vary regionally and seasonally; for example, temperature increases at polar latitudes are expected to be greater than increases near the equator (IPCC 2007a Ch.11). Part of this future warming is inevitable due to the long-lived greenhouse gases that are already present in Earth's atmosphere. However the full extent of warming will depend in part on future emissions of greenhouse gases. The IPCC has developed a range of 'emissions scenarios' to describe several plausible futures that depend on factors like population, economic growth, technological advances, and others. These are frequently used by climate modelers in projecting the ranges of future climate (IPCC 2000). New emissions scenarios are in development and will be used in the upcoming 2013-2014 version of the IPCC report. Average temperatures in the U.S. over the next century are expected to increase by approximately 7 to 11°F (3.9 to 6.1°C) under a higher IPCC emissions scenario and by approximately 4 to 6.5°F (2.2 to 3.6°C) under a lower emissions scenario. (USGCRP 2009 - Figure 7). Both lower and higher temperature changes are possible, if future emissions fall below or above the IPCC emissions scenarios.
Precipitation changes will also vary seasonally and regionally, and are more uncertain than temperature changes. Models project that northern areas in the U.S. will generally become wetter, and southern areas, especially the southwest, will generally become drier (USGCRP 2009). In northern areas, a greater proportion of annual precipitation is expected in the winter and spring, and may fall as rain rather than snow due to warmer temperatures. In the southwest, increased evaporation due to higher temperatures may increase stress on water resources (USGCRP 2009). Across all areas of the United States, the amount of heavy precipitation is expected to increase, especially in the Midwest and northeast, following observed trends from 1958 to present day (Figure 8). Although modeled precipitation projections are improving, there is still a high degree of uncertainty and specific regional patterns could differ substantially from these general trends.
Effects on Ecosystems and Ecosystem Processes
The climate changes expected over the next century will have huge consequences for ecosystems and the benefits they provide, including the provision of wood and fuel, food, temperature and flood regulation, erosion control, recreational and aesthetic value, and species habitat, among others.
Climate changes are likely to affect important ecological processes that will in turn affect key natural resources. For example, temperature and precipitation changes have strong implications for water resources and hydrologic cycling. In addition, disturbances such as insects, wildfire, invasive plants, and forest diseases will become more frequent in some areas of the country. The emissions that cause climate change also lead to air quality problems that put additional stress on trees.
Coupled with altered hydrology and increased disturbance and stress, climate change will affect how vegetation is distributed within the U.S., and will cause changes for aquatic ecosystems, wildlife species and soils. How these resources are affected will have broad implications for maintaining ecosystem services, including biodiversity and the carbon storage capabilities of forests. Each impact on one aspect of an ecosystem can affect a variety of others, producing a series of cumulative effects that can make it difficult for ecosystems to adapt.
Meeting the diverse challenges that climate change is imposing on Earth's environments requires many approaches, and specific responses will depend heavily on the management goals for a particular resource. Scientists are currently working to understand the risks posed to ecosystems, through examining characteristics and changes in landscapes and conducting assessments on impacts and ecosystem vulnerabilities. Public lands, private lands, wilderness areas, and urban neighborhoods will all be affected, and each will require different management considerations. Specific management practices such as silviculture are potentially valuable tools for helping forests respond to a changing climate.
For those charged with managing ecosystems, climate change can seem like a daunting challenge. Fortunately, a range of management options exist to help ecosystems adapt to climate changes, and to contribute to climate change mitigation by reducing the amount of greenhouse gases in the atmosphere. These options are often complementary to actions that land managers employ regularly.
The majority of the CCRC is dedicated describing ecosystem responses to climate change, and how natural resource management may be able to respond to those changes. Please follow the links in the text, or explore the rest of the website for further information.
Need more information?
See the following primers and resources for more introductory information on climate change.
Climate Change Resource Center:
United States Global Change Research Program:
Global Climate Change Impacts in the United States
The US EPA
Climate Change Science Facts
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