Listen to West Regional Pre-release Briefing
Key passages from report released April 16 (North America Chapter)
Key passages from report released April 6 (Impacts)
Key passages from report released February 2 (Science)
North America Chapter of the IPCC's WGII Technical Report:
"Climate Change 2007: Impacts, Adaptation and Vulnerability"
Issued April 16
On April 16, 2007, the Intergovernmental Panel on Climate Change (IPCC) released the North America chapter of the Working Group II technical report in Washington, D.C. This new chapter details the North American findings summarized in the global Summary for Policymakers released on April 6.
Future Impacts and Vulnerabilities
"For most combinations of model, scenario, season, and region, warming in the 2010-2039 time slice will be in the range of 1-3 degrees C. Late in the century, projected annual warming is likely to be 2-3°C across the western, southern, and eastern continental edges, but more than 5 degrees C at high latitudes. The projected warming is greatest in the winter at high latitudes and greatest in the summer in the Southwest U.S. Warm extremes across North America are projected to become both more frequent and longer."
"Warming, and changes in the form, timing, and amount of precipitation will very likely lead to earlier melting and significant reductions in snowpack in the western mountains by the middle of the 21st century [high confidence] In projections for mountain snowmelt-dominated watersheds, snowmelt runoff advances, winter and early spring flows increase (raising flooding potential), and summer flows decrease substantially. Heavily-utilized water systems of the western U.S. and Canada, such as the Columbia River, that rely on capturing snowmelt runoff will be especially vulnerable."
"Heavily utilized groundwater-based systems in the southwest U.S. are likely to experience additional stress from climate change that leads to decreased recharge [high confidence]."
"In the Ogallala aquifer region, projected natural groundwater recharge decreases more than 20% in all simulations with warming of 2.5°C or greater."
"Higher stream temperatures affect fish access, survival and spawning (e.g., west coast salmon)."
Climate change adds challenges to managing the Columbia River system
"Current management of water in the Columbia River basin involves balancing complex often competing demands for hydropower, navigation, flood control, irrigation, municipal uses, and maintenance of several populations of threatened and endangered species (e.g., salmon). Current and projected needs for these uses over-commit existing supplies. Water management in the basin operates in a complex institutional setting, involving two sovereign nations (Columbia River Treaty, ratified in 1964), aboriginal populations with defined treaty rights ("Boldt decision" in U.S. vs. Washington in 1974), and numerous federal, state, provincial, and local government agencies. Pollution (mainly non-point source) is an important issue in many tributaries. The first-in-time first-in-right provisions of western water law in the U.S. portion of the basin complicate management and reduce water available to junior water users. Complexities extend to different jurisdictional responsibilities when flows are high and when they are low, or when protected species are in tributaries, the main stem, or ocean.
"With climate change, projected annual Columbia River flow changes little, but seasonal flows shift markedly toward larger winter and spring flows and smaller summer and fall flows. These changes in flows will likely coincide with increased water demand, principally from regional growth but also induced by climate change. For example, a 2°C warming in the 2040s would increase demand for water in Portland, Oregon by 5.7 million m3/yr with an additional demand of 20.8 million m3/yr due to population growth, while decreasing supply by 4.9 million m3/yr. Long-lead climate forecasts are increasingly considered in the management of the river but in a limited way. Each of 43 sub-basins of the system has its own sub-basin management plan for fish and wildlife, none of which comprehensively addresses reduced summertime flows under climate change.
"The challenges of managing water in the Columbia River basin will likely expand with climate change due to changes in snowpack and seasonal flows The ability of managers to meet operating goals (reliability) will likely drop substantially under climate change. Reliability losses are projected to reach 25% by the end of the 21st century and interact with operational rule requirements. For example, "fish-first" rules would reduce firm power reliability by 10% under present climate and 17% in years during the warm phase of the Pacific Decadal Oscillation. Adaptive measures have the potential to moderate the decrease in April snowpack, but lead to 10-20% losses of firm hydropower and lower than current summer flows for fish. Integration of climate change adaptation into regional planning processes is in the early stages of development."
Agriculture, forestry and fisheries
"Crops that are currently near climate thresholds (e.g., wine grapes in California) are likely to suffer decreases in yields, quality, or both, with even modest warming [medium confidence]."
"Water access is the major factor limiting agriculture in southeast Arizona, but farmers in the region perceive that technologies and adaptations such as crop insurance have recently decreased vulnerability."
"Cold-water fisheries will likely be negatively affected by climate change; warm-water fisheries will generally gain; and the results for cool-water fisheries will be mixed, with gains in the northern and losses in the southern portions of ranges [high confidence]. Salmonids, which prefer cold, clear water, are likely to experience the most negative impacts."
"Late in the century. the projected number of heat wave days in Los Angeles increases from 12 to 44-95."
"U.S. water managers anticipate local, regional, or state-wide water shortages during the next ten years. Threats to reliable supply are complicated by the high population growth rates in western states where many water resources are at or approaching full utilization."
Tourism and recreation
"Early studies of the impact of climate change on the ski industry did not account for snowmaking, which substantially lowers the vulnerability of ski areas in eastern North America for modest (B2) but not severe (A1) warming (5 GCMs, 2050s). Without snowmaking, the ski season in western North America will likely shorten substantially, with projected losses of 3-6 weeks (2050s) and 7-15 weeks (2080s) in the Sierra Nevada of California. The North American snowmobiling industry (US$27 billion) is more vulnerable to climate change because it relies on natural snowfall. By the 2050s, a reliable snowmobile season disappears from most regions of eastern North America that currently have developed trail networks."
"For a 2-3°C warming in the Columbia River Basin and British Columbia Hydro service areas, the hydroelectric supply under worst-case water conditions for winter peak demand will likely increase [high confidence]. However, generating power in summer will likely conflict with summer instream flow targets and salmon restoration goals established under the Endangered Species Act. This conclusion is supported by accumulating evidence of a changing hydrologic regime in the western U.S. and Canada. Similarly, Colorado River hydropower yields likely will decrease significantly [medium confidence]."
Accelerating wildfire and ecosystem disturbance dynamics
"Since 1980, an average of 22,000 km2/yr has burned in U.S. wildfires, almost twice the 1920-1980 average of 13,000 km2/yr (Schoennagel et al., 2004). The forested area burned in the western U.S. from 1987-2003 is 6.7 times the area burned from 1970-1986... Human vulnerability to wildfires has also increased, with a rising population in the wildland-urban interface."
"A warming climate encourages wildfires through a longer summer period that dries fuels, promoting easier ignition and faster spread. Westerling et al. (2006) found that, in the last three decades, the wildfire season in the western U.S. has increased by 78 days, and burn durations of fires >1000 ha have increased from 7.5 to 37.1 days, in response to a spring-summer warming of 0.87°C. Earlier spring snowmelt has led to longer growing seasons and drought, especially at higher elevations, where the increase in wildfire activity has been greatest. In the south-western U.S., fire activity is correlated with ENSO positive phases, and higher Palmer Drought Severity Indices."
"Insects and diseases are a natural part of ecosystems. In forests, periodic insect epidemics kill trees over large regions, providing dead, desiccated fuels for large wildfires. These epidemics are related to aspects of insect life cycles that are climate sensitive."
North American cities
"Since most large North American cities are on tidewater, rivers or both, effects of climate change will likely include sea level rise (SLR) and/or riverine flooding. The largest impacts are expected when SLR, heavy river flows, high tides, and storms coincide."
"In southern California, additional summer electricity demand will intensify inherent conflicts between state-wide hydropower and flood-control objectives."
"By the 2020s, 41% of the supply to southern California is likely to be vulnerable to warming from loss of Sierra Nevada and Colorado River basin snowpack."
"Annual precipitation has increased for most of North America with large increases in northern Canada, but with decreases in the southwest U.S., the Canadian Prairies, and the eastern Arctic."
"Streamflow in the eastern U.S. has increased 25% in the last 60 years, but over the last century has decreased by about 2%/decade in the central Rocky Mountain region. Since 1950, stream discharge in both the Colorado and Columbia river basins has decreased, at the same time annual evapotranspiration (ET) from the conterminous U.S. increased by 55 mm."
"The fraction of annual precipitation falling as rain (rather than snow) increased at 74% of the weather stations studied in the western mountains of the U.S. from 1949-2004."
"April 1 snow water equivalent (SWE) has declined 15-30% since 1950 in the western mountains of North America, particularly at lower elevations and primarily due to warming rather than changes in precipitation."
"Streamflow peaks in the snowmelt-dominated western mountains of the U.S. occurred 1-4 weeks earlier in 2002 than in 1948."
"Relative sea level is rising in many areas, yet coastal residents are often unaware of the trends and their impacts on coastal retreat and flooding."
"Many coastal areas in North America are potentially exposed to storm-surge flooding."
"Under El Niņo conditions, high water levels combined with changes in winter storms along the Pacific coast have produced severe coastal flooding and storm impacts. At San Francisco, 140 years of tide-gauge data suggest an increase in severe winter storms since 1950 and some studies have detected accelerated coastal erosion."
Agriculture, forestry, and fisheries
"In California, warmer nights have enhanced the production of high-quality wine grapes, but additional warming may not result in similar increases. For twelve major crops in California, climate fluctuations over the last 20 years have not had large effects on yield, though they have been a positive factor for oranges and walnuts but negative for avocados and cotton."
"In semi-arid forests of the south-western U.S., growth rates have decreased since 1895, correlated with drought from warming temperatures. Relationships between tree-ring growth and climate from 1895-1991 had complex topographic influences in sub-alpine forests in the Pacific Northwest. On high elevation north-facing slopes, growth of sub-alpine fir and mountain hemlock was negatively correlated with spring snowpack depth and positively correlated with summer temperatures, indicating growing season temperature limitations. On lower elevation sites, however, growth was negatively correlated with summer temperature, suggesting water limitations. In Colorado, aspen have advanced into the more cold-tolerant spruce-fir forests over the past 100 years."
"Cold- and cool-water fisheries, especially salmonids, have been declining as warmer/drier conditions reduce their habitat. The sea-run salmon stocks are in steep decline throughout much of North America. Evidence for impacts of recent climate change is rapidly accumulating. Pacific salmon have been appearing in Arctic rivers. Salmonid species have been affected by warming in U.S. streams."
Infrastructure and extreme events
"Flood hazards are not limited to the coastal zone. River basins with a history of major floods (e.g., the Sacramento, the Fraser, the Red River, the upper Mississippi), illustrate the sensitivity of riverine flooding to extreme events and highlight the critical importance of infrastructure design standards, land use planning, and weather/flood forecasts."
Tourism and recreation
"Wildfires in Colorado (2002)... caused tens of millions of dollars in tourism losses by reducing visitation and destroying infrastructure. Similar economic losses were caused by drought-affected water levels in rivers and reservoirs in the western U.S...."[top of page]
The IPCC's "Climate Change 2007: Impacts, Adaptation and Vulnerability"
Issued April 6
Working Group II of the Intergovernmental Panel on Climate Change released this part of the IPCC's Fourth Assessment Report on April 6.
"Climate Change 2007: Impacts, Adaptation and Vulnerability" summarizes current knowledge about impacts of climate change that have already been observed. It also projects future impacts, based on scenarios in which no explicit actions are taken to address global warming and activity continues on a business-as-usual path. That is, the projections assume that climate change impacts are not mitigated by actions such as cuts in greenhouse gases nor by policies that would enhance adaptability to global warming.
The report includes these statements about continent-scale and global-scale changes that relate to issues of concern in the Western United States.
"Drought-affected areas will likely increase in extent. Heavy precipitation events, which are very likely to increase in frequency, will augment flood risk [high confidence]."
"In the course of the century, water supplies stored in glaciers and snow cover are projected to decline, reducing water availability in regions supplied by meltwater from major mountain ranges, where more than one-sixth of the world population currently lives [high confidence]."
"Coasts are projected to be exposed to increasing risks, including coastal erosion, due to climate change and sea-level rise and the effect will be exacerbated by increasing human-induced pressures on coastal areas [very high confidence]."
"The most vulnerable industries, settlements and societies are generally those in coastal and river flood plains, those whose economies are closely linked with climate-sensitive resources, and those in areas prone to extreme weather events, especially where rapid urbanisation is occurring [high confidence]."
[Following passages from the report's North America section:]
"Moderate climate change in the early decades of the century is projected to increase aggregate yields of rain-fed agriculture by 5-20%, but with important variability among regions. Major challenges are projected for crops that are near the warm end of their suitable range or depend on highly utilised water resources [high confidence]."
"Warming in western mountains is projected to cause decreased snowpack, more winter flooding, and reduced summer flows, exacerbating competition for over-allocated water resources [very high confidence]."
"Disturbances from pests, diseases, and fire are projected to have increasing impacts on forests, with an extended period of high fire risk and large increases in area burned [very high confidence]."
"Cities that currently experience heat waves are expected to be further challenged by an increased number, intensity and duration of heat waves during the course of the century, with potential for adverse health impacts. The growing number of the elderly population is most at risk [very high confidence]."
"Coastal communities and habitats will be increasingly stressed by climate change impacts interacting with development and pollution. Population growth and the rising value of infrastructure in coastal areas increase vulnerability to climate variability and future climate change, with losses projected to increase if the intensity of tropical storms increases. Current adaptation is uneven and readiness for increased exposure is low [very high confidence]."[top of page]
The IPCC's "Climate Change 2007: The Physical Science Basis"
Issued Feb. 2
The IPCC's new report includes these statements about global-scale changes that relate to issues of concern in the West, such as weather extremes and sea level rise. The summary issued Feb. 2 does not have region-level projections for the U.S.
"The frequency of heavy precipitation events has increased over most land areas, consistent with warming and observed increases of atmospheric water vapour."
"Widespread changes in extreme temperatures have been observed over the last 50 years. Cold days, cold nights and frost have become less frequent, while hot days, hot nights, and heat waves have become more frequent."
"More intense and longer droughts have been observed over wider areas since the 1970s, particularly in the tropics and subtropics. Increased drying linked with higher temperatures and decreased precipitation have contributed to changes in drought. Changes in sea surface temperatures (SST), wind patterns, and decreased snowpack and snow cover have also been linked to droughts."
"It is very likely that hot extremes, heat waves, and heavy precipitation events will continue to become more frequent." (In IPCC terminology, "very likely" means a probability greater than 90 percent.)
"Snow cover is projected to contract. Widespread increases in thaw depth are projected over most permafrost regions."
For more IPCC excerpts see Extreme Weather.
Sea level rise
"Both past and future anthropogenic carbon dioxide emissions will continue to contribute to warming and sea level rise for more than a millennium, due to the timescales required for removal of this gas from the atmosphere."
For more IPCC excerpts see Hurricanes and Sea Level Rise.[top of page]
Washington, Oregon, Idaho and the Columbia River Basin
Climate Impacts Group (http://www.cses.washington.edu/cig/), "an interdisciplinary research group studying the impacts of natural climate variability and global climate change ("global warming") on the U.S. Pacific Northwest."
Colorado, Utah, Wyoming
Western Water Assessment (http://wwa.colorado.edu/index.html), which works "to identify and characterize regional vulnerabilities to climate variability and change" in the Intermountain West.
New Mexico, Arizona
CLIMAS: Climate Assessment for the Southwest (http://www.ispe.arizona.edu/climas/), "established to assess the impacts of climate variability and longer-term climate change on human and natural systems in the Southwest."
"Heat Invades Cool Heights Over Arizona Desert"
New York Times, March 27, 2007
The California Climate Change Portal (http://www.climatechange.ca.gov/), an entryway to a variety of information sources, including the 2006 report, "Our Changing Climate: Assessing the Risks to California."
The U.S. Environmental Protection Agency produced individual information sheets in 1998, presenting the agency's then-current assessment of past and possible future impacts of climate change in each state. PDF files can be downloaded here:
The U.S. National Assessment of the Potential Consequences of Climate
Variability and Change was published by the federal government in 2001. It included information for 19 regions and nine mega-regions of the country. Those regional reports can be downloaded here:
Climate and Farming.org, a website produced by Cornell University, the University of Vermont and other partners about climate change and Northeast agriculture, provides resources and links relevant to agriculture in other regions, too.
"Heat - The Number One Non-Severe Weather Related Killer in the United States"
provides detailed background information on heat waves. The article was published in
2006 in the National Oceanic and Atmospheric Administration's NOAA Magazine.
Examples of region-related research
Trends in Snowfall versus Rainfall in the Western United States
Knowles, N., et al. (2006)
Click here to download PDF: http://tenaya.ucsd.edu/~dettinge/jclim_rain_v_snow.pdf
Excerpt: "If warming continues and raises the mean winter wet-day minimum temperatures in more of the West above about -5C, snowfall declines (and rainfall increases), combined with earlier melting of the remaining accumulations of snowpack, will diminish the West's natural freshwater storage capacity. The shift from snowfall to rainfall also may be expected to increase risks of winter and spring flooding in many settings."
Declining Mountain Snowpack in Western North America
Mote, P., et al. (2005)
Click here to download PDF:
Excerpt: "It is becoming ever clearer that these projected declines in SWE (snow water equivalent), which are already well underway, will have profound consequences for water use in a region already contending with the clash between rising demands and increasing allocations of water for endangered fish and wildlife."
Warming and Earlier Spring Increase Western U.S. Wildfire Activity
Westerling, A., et al. (2006)
Excerpt: "We show that large wildfire activity increased suddenly and markedly in the mid-1980s, with higher large-wildfire frequency, longer wildfire durations, and longer wildfire seasons. The greatest increases occurred in mid-elevation, Northern Rockies forests, where land-use histories have relatively little effect on fire risks and are strongly associated with increased spring and summer temperatures and an earlier spring snowmelt."
A Semi-Empirical Approach to Projecting Future Sea-Level Rise
Rahmstorf, S. (2006)
Abstract available here: http://www.sciencemag.org/cgi/content/abstract/315/5810/368
BBC News: "Current sea level rise projections could be under-estimating the impact of
human-induced climate change on the world's oceans, scientists suggest. By plotting
global mean surface temperatures against sea level rise, the team found that levels could
rise by 59% more than current forecasts."
CALIFORNIA [top of page]
Dr. Peter H. Gleick
President, co-Founder, Pacific Institute
climate change, water resources, adaptation, impacts on California
Professor Burton Richter
Senior Fellow, Freeman Spogli Institute for International Studies
Paul Pigott Professor Emeritus in the Physical Sciences
Nobel Laureate, Physics, 1976
Ph: 650-926-2601 (office hours are 8:30-15:30, PDT, M-F)
Please cc: firstname.lastname@example.org
Terry L. Root
Senior Fellow (University Faculty), Woods Inst. for the Environment
Professor by courtesy, Biological Sciences
Robert C. Wilkinson
Director, Water Policy Program
Bren School of Environmental Science and Management
University of California, Santa Barbara
805 569 2590
California impacts, water policy
Department of Global Ecology
(650) 462 1047 x 201
COLORADO [top of page]
"Wilting under the heat: Global warming blamed for deaths of trees in area"
Durango Herald, Oct. 15, 2005
Susanne C. Moser, Ph.D.
Institute for the Study of Society and Environment (ISSE)
National Center for Atmospheric Research
MONTANA [top of page]
Steven W. Running
Director, Numerical Terradynamic Simulation Group
Dept. of Ecosystem Sciences
University of Montana
Terrestrial carbon cycles
OREGON [top of page]
Director, Climate Change Science
The Nature Conservancy
Cell: (206) 604-5549
(available April 1)
UTAH [top of page]
"Hotter Utah - not all bad?"
Deseret News, March 18, 2007
"Governor's panel hears global warming warning"
The Salt Lake Tribune, March 15, 2007
WASHINGTON [top of page]
Edward Miles, Ph.D.
Professor of Marine Studies and Public Affairs
Co-Director, Center for Science in the Earth System
Principal, Climate Impacts Group
University of Washington
Peter B. Rhines, Ph.D.
Professor of Oceanography and Atmospheric Sciences
University of Washington
Climate dynamics; high altitude climate
Nickels' watershed view: City's supply OK for now
Seattle Times, March 29, 2007
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