Climate models can’t read the story of Rainier

Global climate models agree that temperatures will rise in the Pacific Northwest through the 21st century.

But making specific and accurate predictions for an area as small and unusual as Mount Rainier National Park is beyond the scope of current climate knowledge and computing power.

The park is essentially a square that measures about 20 miles on a side, with a mountain in the middle. Global climate models — mathematical representations expressed in computer code — are broad overviews that offer projections on scales many times that size and don’t address such local aberrations.

Climate scientists are refining global models to smaller scales, but the complexities in Washington are enormous. Mountain ranges complicate things, and so do the Pacific Ocean and Puget Sound.

Washington’s weather varies widely by year — and even by decade — because of the influence of heat circulation patterns in and above the Pacific Ocean, which are not fully understood.

Temperature and precipitation patterns flip back and forth on a fairly regular basis because of natural sea-surface temperature shifts called the El Nino-Southern Oscillation and the Pacific Decadal Oscillation.

Making predictions for Mount Rainier is especially difficult because of its great height. At 14,411 feet, the mountain creates its own weather.

Climbing from the bottom of the mountain to the top is the climate equivalent of traveling from Washington to the Arctic Circle.

So far at least, models can’t resolve the park’s topography with enough detail to predict how the climate of different places within it might change.

Rainfall and temperatures on the mountain vary widely from top to bottom and even from one valley to the next, depending on terrain and sun exposure.

Paradise, at an elevation of 5,400 feet, gets an average of 126 inches of rain a year. Longmire at 2,761 feet, gets just 87 inches.

The eastern side of the mountain is much drier than the western side, making average temperatures for the park as a whole of little use.

Downscaled climate models can be crosschecked for accuracy by using historical records, but Mount Rainier’s records don’t go back very far.

Eleven weather stations gather data in the park, but only the station at Longmire has been operating long enough (since 1909) to show trends that climatologists say are significant.

Data from high elevations is especially scarce.

Generally, though, the evidence indicates Mount Rainier will warm along with the rest of the Northwest, with average warming of between 3 and 6 degrees by the end of the century.

Some models, but not all, indicate that for the Northwest generally, the amount of precipitation is likely to increase and that more of it will fall as rain and less as snow.

That might not be the case for everywhere at Mount Rainier, however.

Cliff Mass, atmospheric science professor at the University of Washington, says that while climate change will push the freezing level higher on Mount Rainier, its upper reaches could very likely get more snow, not less.

“Because of its height, snowfall on the upper slopes could increase since precipitation will increase and those slopes will remain cold enough for snow,” Mass said. “The snow level on its lower slopes will rise, as with the rest of Cascades.”

Some models but, again, not all, predict more “extreme” weather events — heavy downpours and violent storms.

They also predict the number of freeze-free days each year will increase and that less rain will fall in summer months. The number of consecutive days without rain is likely to increase.

All models do agree on this: The amount of change will depend to a large extent on the rate at which humans continue to put greenhouse gases into the atmosphere.

According to the Intergovernmental Panel on Climate Change, if all human-generated greenhouse gas emissions ended immediately, about half of the carbon dioxide would be removed from the atmosphere within 30 years. The rest will stay for centuries.

Analyzing how Mount Rainier might react to climate change differently than the rest of the Northwest is a mostly unexplored area.

However, according to a draft report prepared this year for the National Park Service by the University of Washington’s Climate Impacts Group, the historical record contains some surprises.

As a whole, the Pacific Northwest warmed by 1.4 degrees between 1920 and 2000. Longmire warmed, too, but only .5 degree.

More surprising, while maximum temperatures climbed at Longmire, minimum cold temperatures fell. That was a big surprise to climate scientists, who expected just the opposite, based on models.

Evidence of a long-term warming trend at Mount Rainier is obscured by recent periods of lower temperatures and higher than usual snowfall.

While Longmire records show a slight warming trend over the past century, records at Paradise show the average temperature dropped — about 1 degree during that time.

The park’s weather stations show no significant trends in either precipitation or snow depth since 1970.

Many of Mount Rainier’s glaciers either stopped retreating or advanced between the early 1950s and the mid-1980s.

In the 1970s, spectacularly high snowfalls on the mountain set two new world records.

Eighty-five feet of snow fell at Paradise in 1971. The next winter set a new record of more than 94 feet. Another spectacular snowfall occurred in 1974, with more than 90 feet.

In 2010 and 2011, when weather at the park was influenced by strong La Nina conditions, the Nisqually and Emmons glaciers grew in volume. In 2011, mountain lakes stayed frozen longer than in the previous six years of record keeping.

Climate scientists say those conditions were short-term aberrations that are part of natural climate variation and do not change long-term warming trends.

Still, they’re enough to provide footholds for those who deny that global warming is a reality.

There’s no denying that Mount Rainier’s glaciers are receding over the long term and that very small changes in the climate have big effects on the ice.

“Ice volume has been declining since the end of the Little Ice Age (about 1850),” said Thomas Sisson, a U.S. Geological Survey scientist who has studied Rainier’s glaciers. “But there were periods of stasis or modest advance that appear to correlate with strong cool phases of the Pacific Decadal Oscillation.

“The glaciers are getting smaller,” Sisson said, “so it looks like near-average temperature and near-average snowfall are insufficient to maintain ice volume.”