Pacific Northwest 

-- An overview prepared by Phil Mote, Ph.D. (University of Washington) and Blair Henry (Northwest Council of Climate Change) --
 

Climate and changes in it – regardless of their cause – matter to people, communities and businesses. Global warming is likely to bring many changes to the nation. The United States as a whole is in a strong economic position to adapt to many of these changes, but adaptation is often expensive, not always possible or successful, and during transitions ecosystems, communities, and individuals could suffer. Moreover, national impact summaries disguise local dislocations and disruptions to the ways we live, work and recreate. Climate change adds a serious stress to our already threatened resources and treasured places. Overall impact statements also mask significant opportunities. To minimize the negative changes and make the most of the positive changes we need to take a close look at how climate change will affect each region. How will the Pacific Northwest experience the effects of global warming? And how can we respond?

Climate change and the Pacific Northwest

Despite its reputation for rain, the Pacific Northwest (PNW) experiences dry summers, and irrigated agriculture, urban users, and ecosystems rely on snowmelt for summer water.  This fact is critical in understanding how the region responds to climate.

Year-to-year and decade-to-decade variations in PNW climate are influenced by two patterns of Pacific climate variability: El Niño-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). ENSO and PDO each tend to push PNW climate toward one of two main patterns: cool-wet or warm-dry. 

Impacts of climate variations (ENSO, PDO – see text) on the Northwest.  The top panel shows the impacts of sea surface temperature (SST) conditions over the North Pacific associated with the warm phase of ENSO or PDO, and the bottom panel shows the impacts of the cool phase.

The warm-dry winters have thinner snowpack and lower spring and summer streamflow, with generally negative impacts on salmon and forests.  The cool-wet winters have the opposite effects.  Even though the annual temperature and precipitation fluctuations associated with the PDO (Figure 2) are fairly small, these small changes in climate have large impacts on the region’s natural resources. 

Natural Columbia River flow at present (dashed), and in 2050 as simulated under future climate conditions from four climate models.

During the past 100 years, the PNW has become warmer and wetter.  The region’s average temperature has increased 1.5°F, and average precipitation has increased about 3” (15%).  Scientists cannot be sure what has caused these increases, but the increases are consistent with trends generated by climate models using observed increases in carbon dioxide.  Climate models project continued increases in temperature and winter precipitation.  Summer precipitation could go up or down.

What effects will these climatic changes have? 

For the PNW, the most significant consequence of climate change is likely to be the reduction in all-important summer water supply.  As the climate warms, snowpack will shrink and summer streamflow will drop considerably.  This and other climate changes will have a wide range of consequences, most of them negative, for humans and ecosystems.

Water resources
The benefits to dryland agriculture of a longer growing season and greater precipitation may be offset by the losses to irrigated, high-dollar-value crops. Past experience offers some lessons: In the dry Yakima Valley of Washington, a string of years with below-average snowpack (1991-1994) led to selective water shortages and economic losses that reached $140 million in 1994.  Even though water will become less plentiful in summer, higher winter precipitation (as occurred during the winter of 1998-99) will probably also increase wintertime flooding in many rivers. 

Salmon
Climate variations have clearly played a role in PNW salmon history (Figure 2), with low summer streamflow and warm coastal ocean temperatures tending to reduce salmon production.  Unfortunately, these conditions are likely to become more common in a warming climate, adding to the already long list of human-caused problems that now threaten the survival of salmon in the PNW.

Forests
Some types of  trees grow better with more carbon dioxide in the air, but for most Northwestern coniferous forests, growth tends to be lower (and forest fires more extensive) during warmer, drier years (Figures 1 and 2).  It is not yet clear how forests will change in the future, but some changes in forest composition, area, and density are likely.

Coasts
Both the physical landscape and the ecosystems of the coasts will be affected by climate change and rising sea level.  Changes in wave direction may increase coastal erosion, as often happens during El Niño events.  Increased winter precipitation will probably lead to more frequent landslides; recent wet winters have shown that thousands of homes are at risk from landslides around Puget Sound and on the Oregon coast, and climate models consistently project wetter winters. 

What would we have to do to prepare for a changing climate?
 

Climate scientists agree that further climate change may be inevitable and will therefore require adaptation, although most scientists also think that the pace of climate change can be slowed by substantially reducing greenhouse gas emissions. This would give governments, businesses, and ecosystems around the world more time to respond and adapt to climate change as well as reducing the overall severity of climate change-related impacts, thereby buying "insurance" for an uncertain future.  Another way to buy insurance now is to incorporate climate change into all long-term decisions about natural resources, thereby providing greater resilience.

Climate change is sure to occur in some form.  Though the details are not yet clear, we know enough already to begin planning.  With few exceptions, natural resources are managed as if climate were constant. Recent experience with year-to-year climate variations, like those associated with El Niño, provides some practice at dealing with years when climate is different from “normal.”  In years ahead we will see a change in the definition of “normal.”  The single most important thing that the region can do to prepare for a changing climate is to develop a dialogue between scientists and decision-makers.  An increased awareness of how climate affects the region will increase resilience to climate variations and change. In addition, we can reduce local pressures on our resources and ecosystems.

Water resources
Three basic strategies should be examined: to increase supply, to decrease demand, and to increase institutional flexibility.

Salmon and forests
Ecosystems are more resilient to climate variations and change when they include a high degree of biodiversity, that is, a wide range of different habitats, species, and genetically different types within the same species.  For salmon, ensuring biodiversity mostly means increasing available healthy and connected habitat while continuing to control harvests.  For forests, ensuring biodiversity means avoiding single-species plantations.

Coasts
A wide range of coastal problems could be dealt with by changing land-use controls, construction setbacks, and zoning.  Public funds could be better spent in ways other than subsidizing coastal development (especially re-development after damage) in obviously hazardous places.

Additional information

For more information on the potential impacts of global warming on the Pacific North West, several experts are available to answer your questions:

Philip Mote, Ph.D., University of Washington, Climate Impacts Group
 Tel.: (206) 616-5346  Fax.: (206) 616-5775  Email: philip@atmos.washington.edu

Blair Henry, Northwest Council on Climate Change
 Tel. (206) 547-3871    Fax.: (206) 634-3192   Email: blairhenry@msn.com