Six degrees of... devastation?

For once the headline on the press release actually understated the story beneath. "Projected snowpack decline could mean drastic changes for region," read the announcement about a paper presented June 4th by two University of Washington scientists to a meeting of the American Geophysical Society (read the paper). But the research by Dennis Lettenmaier and Alan Hamlet of the U's Civil and Environmental Engineering Department wasn't just bad news for ski-area owners. It also bodes big changes for the rest of the 12 million people who dwell in the Pacific Northwest.

Based on sophisticated computer climate models from England and Germany, the UW study predicts what's likely to happen to snowpacks and stream flows in three states and one Canadian province over the next 100 years, and its results are expressed in charts and graphs hard for an average reader to decipher. But it's clear at least that Northwest residents and transients, too, like salmon returning home to spawn, will no longer be able to take for granted that water will be there when and where they need it.

Another model, devised at a lab closer to home, goes farther and spells out just what we're likely to be in for climate-wise. According to Ruby Leung and her colleagues at the Department of Energy's Pacific Northwest National Laboratory in Richland, by the year 2080 the state of Washington will be experiencing:

* Average summer temperatures two degrees higher than at present,
* Average winter temperatures three to five degrees warmer,
* A rise in the average snow line from around 3,000 to over 4,000 feet, with a consequent
* 50 percent decrease in total average winter snow cover statewide, with a
* 50 to 90 percent decrease in the mountain snowpack below 4,000 feet.

At first glance, that doesn't seem like such hot stuff: bad news for winter sports fans, sure, but how much impact could a couple of degrees of warming have down here on the flatlands? An awful lot, unfortunately. You don't notice five degrees one way or the other when the temperature's in the 50s or 60s or even 70s. But the difference between 85 and 90 or 29 and 34 is not just noticeable, it changes the ground rules for life in these parts, threatening signature ecosystems (the Olympic rain forest) and key industries (the Skagit delta's bulb farms, Eastern Washington's orchards) while encouraging species we're currently happy to do without (mosquitoes, disease-bearing ticks).

People are flexible by nature. Other animals and plants are downright cranky about what conditions they prefer. A shift of a couple of degrees can make it too hot for a tree or plant to germinate properly, or for the bug which pollinates it to reproduce. That doesn't mean that all the hemlock trees or honey bees suddenly drop dead; it does mean that they shift their favored base of operations. Deciduous trees penetrate further up the mountain slopes, while conifers move in on rocks where previously only lichens grew. Ponds dry up. Sage moves in on meadowlands.

Thanks to generations of botanists like the UW's Estella Leopold collecting and cataloging the pollen of long-departed vegetation from lakes and bogs, we know a lot about what kind of vegetation flourished where and when in the ancient Northwest. The sparse grass and scrubby shrubs of glacial-age Puget Sound indicate that when human beings first moved into the neighborhood some 12,000 years ago, conditions were not only a lot colder but considerably drier as well. As things warmed up over the next 5,000 years or so, rainfall increased, too. Both reached peaks about 4000 BC, when winters were colder and summers warmer than today, then fell gradually as temperature extremes narrowed toward present temperate conditions.

The trouble with predicting the effect of the warming Leung's model suggests is that it has no precedent—at least since the Eocene era some 50,000,000 years ago, when, geologically, the Northwest was only just rising from the sea. But you don't need precedents to see where the predicted climate change will first impact the human ecology of the Northwest.

Since hunter-gatherers squatted beside the rapids waiting for the salmon, people in this part of the world have lived their lives in accord with the delicate balance between each winter's snowfall and the next summer's run-off. Every Northwest river has its own typical annual high- and low-water curve, but all exhibit the same general pattern: low stream flow in February, when cold locks up most precipitation in snow and ice, rising to a sharp peak in early June, when up to six times as much water fills their beds. Since early in this century we've invested incalculable billions of dollars in the form of dams to exploit this pattern—to generate hydroelectric power, support irrigated agriculture, quench the thirst of factories and cities.

Unfortunately, according to Leung's results, the pattern is almost certain to change. Even assuming that "global" part of "global warming" doesn't impact total precipitation over the region—the models aren't yet advanced enough to say much about that—warmer winters mean lower snowpacks and more rapid winter runoff, leaving less total contribution for stream flows in summer. The whole curve flattens out, and peak runoff comes earlier in the year. Our present system, elaborate as it is, still depends on mountaintops more than reservoirs for storage. "If you lose the snow storage, you need storage from somewhere else," Lettenmaier told his Boston audience. "But from an environmental standpoint, no one is ready to run out and build more dams."