State Senate workshop on climate change
Impacts of climate change on Washington's forests, salmon, coasts, and human health
Philip Mote
March 26, 1999

Ruby and Alan provided you with a brief summary of the impacts climate change is likely to have on the region's water resources, and Ruby mentioned some of the impacts on agriculture. I will touch briefly on the impacts it could have on the region's forests, salmon, coasts, and human health.

Forests

For forests, a number of factors in future climate may be important. First, higher levels of carbon dioxide may increase the growth of plants in the short term, according to some studies. However, many other studies have shown that in the long run, elevated CO2 may reduce production. Of course, other changes may not be beneficial, and the changes suggested by climate models are likely to diminish forest productivity and forested area.

Most of the climate scenarios I described earlier had warmer summers with a decrease or at most a small increase in rainfall, which suggests that the soil would be drier and the trees would lose moisture more rapidly. Drought is bad for trees in a number of ways: it increases susceptibility to insect attack, and increases the risk of forest fires both by killing parts of trees and by drying existing fuel. Increases in winter temperature allow insects and pathogens to survive.

One recent study of the forests in Washington State indicated the changes in species that could occur if the temperature rose 2.5oC or 5.0oC. Tree species have preferred climatic conditions under which they thrive. If conditions change, big trees can survive long after the conditions are no longer optimal, but it is the seedlings that suffer: they cannot get started in the wrong climate conditions. Slow attrition results. With a slow change in climate, species could migrate up the mountainsides or northward, following climate conditions, but these migrations take far longer than unnatural climate change is occurring; furthermore, species migrating up find themselves restricted to smaller areas. In the past, changes in temperature and precipitation smaller than those projected by the climate models have caused major shifts in species ranges and relative abundances.

The figure shows the possible impacts that increases in temperature would have on the eastern slopes of the Cascades. The boxes above the zero line indicate alpine and forest zones, and below the line are savanna and steppe zones. A warming of 2.5oC (about 5oF, projected to occur by about 2050) could reduce the forested area by half, converting once commercially valuable forests into brush-covered steppe. With a warming of 5oC (9oF), Mountain Hemlock and alpine ecosystems all but disappear, and forested area diminishes to 20% of its current area. Changes in the Olympics and West of the Cascades would not be as dramatic because these are wetter climates, but could still be significant, especially if a long drought led to really big fires.

But there's more to the story than changes in temperature. Reduction in snow cover could have a variety of effects, some positive and some negative. Different climatic zones have different limiting factors. In areas of deep snow (the western Cascades, Olympics, and high elevations of the region's other mountains), a reduction in snowpack lengthens the growing season, giving seedlings a better chance at establishment. In dry areas (the eastern Cascades and the Blue Mountains) soil moisture is the limiting factor, and a reduction in snowpack would probably reduce springtime soil moisture, making it more difficult for seedlings to get established. Of course, these are not just trees we're talking about, but the livelihoods of thousands of people too.

Salmon

Salmon are very much on everyone's minds these days. But how will climate change affect salmon? The answer is even more difficult than for forests, partly because salmon are harder to study than trees; they don't stay in one place very long, and they spend much of their lives out at sea. So we don't have a clear picture of just how climate affects salmon, but some important clues are emerging.

Salmon are sensitive to a variety of different climate variables at different times in their complex life cycle. The eggs are vulnerable to fall and winter floods, which can scour the river bed and damage or destroy the eggs. Adults must survive in the ocean. The migrating smolts, or juveniles, are apparently the most vulnerable to climate, as they undergo physical changes in response to the change from fresh water to salt water while learning to find food in their new environment. The timing of their arrival in the coastal waters may play a big role in their survival. For example, if they arrive before the summer northerly winds begin, which bring up nutrient-rich bottom water, the migrating smolts will not have enough food. If the smolts arrive too late, the best food may already be gone.

Salmon throughout the North Pacific show clear sensitivity to a slow climate variation called the Pacific Decadal Oscillation, or PDO. The PDO tends to stay in one pattern for 20-30 years, then switch to the other pattern for 20-30 years. Switches have occurred in 1925, 1945, and 1977. One of the key findings of our research group at UW was the connection between the PDO and salmon production. Bad years for salmon production in Washington tend to be good years for salmon production in Alaska, and vice versa. In particular, the period from 1945-76 was relatively good for our chinook and coho, but bad for Alaskan sockeye and pink salmon. Since 1977, though, salmon here have been on the decline while salmon in Alaska have been more abundant. There is strong evidence that climate has played a role in determining salmon abundance.

A number of factors about the PDO may be important in influencing our salmon, and these are important analogies to use in thinking about climate change. First, salmon are temperature-sensitive. The 1945-76 period was one of slightly cooler ocean and land temperatures in Washington. Second, smolts arriving in the ocean appear to do better when they arrive to find a ready food supply, which depends partly on when the summer northerlies begin; in the cool-phase PDO, the conditions on their arrival appear to be better. It is not clear from the GCMs whether this will be a characteristic of future climate, but from what we can tell, it seems unlikely.

Third, salmon have evolved to take advantage of the natural rhythm of streamflow. Having disturbed that rhythm by building dams, and now managing those dams differently to account for the needs of salmon, we will find that climate change further disturbs that rhythm. For example, out-migrating smolts of some runs rely on the spring snowmelt for a quick trip down the river. If that occurs a month or two earlier, as Alan showed, climate change could pose a further hardship.

In summary, to the extent that we understand the ways in which climate affects salmon, the changes in climate that are projected to occur in the Northwest would be mostly bad news for salmon. Increased winter flooding, decreased summer and fall streamflows, increased temperatures in the streams and the ocean, and possible reduction in upwelling of nutrient-rich water all would take their toll on salmon. Of course, these are not just salmon we're talking about, but the livelihoods of thousands of people too.

Coasts

The third aspect of climate change impacts that I will discuss is Washington's coasts. Current projections of global sea level rise by 2100 are 8-36 inches, compared to 4-10 inches observed during the last century. Because of vertical land movements, any given location may experience very different sea level changes. For example, the Olympic Peninsula is rising at a rate of about 12 inches per century so that sea levels are presently decreasing, while southern Puget Sound (including Olympia) is sinking at 8-16 inches per century, exacerbating sea level rises. Olympia is perhaps the most vulnerable place in the Puget Sound area to sea level rises. Large areas of downtown would be inundated by 2100 under current projections of sea-level rise without substantial investment in building dikes.

Sea-level rises are not the only factor with the potential to affect coastal areas. In low-lying areas, the frequency of storm surges may be more significant than sea-level rise alone. Landslides are caused by a variety of factors in different places, but one common cause of landslides is a long period of above-normal rainfall, leading to saturated soils, followed by a heavy rainfall. The heavier winter rainfall projected by the models suggests an increase in saturated soils and landslides. During the wet winter of 1996-97, and again this winter, a number of homes were damaged or destroyed in the Puget Sound area by mudslides.

Human health

Finally, let me discuss briefly the possible impacts of climate change on human health in the Northwest. This is the area of research in which our group has the farthest to go, and at this point we can only speculate. Increases in temperature would reduce cold-related deaths and injuries, but would increase heat-related deaths and injuries especially in Eastern Washington. Warmer coastal waters have already been linked to increases in shellfish poisoning, and other kinds of food poisoning are more common in warmer climates. Diseases characteristic of warmer climates, like malaria, might become more common here. Other aspects of human health may be more subtle: for instance, the secondary role that climate may play in our levels of stress if it increases population growth as people leave hotter areas to the south, or the possible connection between climate and levels of stress and suicide. Most people I have talked to about the climate change scenarios projected by the models react to the news of wetter winters with the words, ``That's depressing.''

Summary

In summary, climate change could have a wide range of impacts on Washington state and on a wide range of activities and resources. Ecosystems, human activities, and human infrastructure are all built around the assumption that the future will be like the past. For example, we account for flood histories, temperature extremes, and snow loads when constructing buildings or locating infrastructure. But what happens if the hundred-year flood becomes the five-year flood? It might not be prudent to build there. Or what happens if the five-year flood becomes the hundred-year flood? It might not be prudent to spend as much money building protective structures.

You make decisions every session on issues concerning the state's natural resources and infrastructure. We hope you will consider how climate change might affect these issues.