Global Warming: Potential Effects on National Parks in the Pacific Northwest Cliff Mass, Department of Atmospheric Sciences University of Washington

Global Warming and the Northwest National Parks Some potential impacts that have been mentioned: – More windstorms, with increased damage to forests and coastal zones – Heavier rain, with more flooding events. – Reduced snowpack, and earlier spring melt. – Reduction in number and extent of glaciers.

Questions Have we seen such impacts during the past few decades? What should we expect during the remainder of this century?

The Bottom Line Global warming is an extraordinarily serious global issue, but some areas will have lesser or greater effects. The Northwest may well be a location where GW effects are delayed and weaker than the global average. At this point in time, we are not able to demonstrate that global warming has produced measurable impacts on Northwest weather and climate.

The Bottom Line The impact of global warming over the Northwest during the next few decades is not clear. Impacts, specifically on snowpack and glacier extend, should be large by the middle to end of the century.

Floods The November 6, 2006 floods at Mount Rainier and the December 3, 2007 flooding of Chehalis and Centralia has sensitized us to this threat. The hand-waving argument is that warming temperatures will result in more water vapor in the atmosphere, heavier rain, and more floods. Reality is much more complicated.

What does the data show? Coastal Rainfall: The trend in the number of events greater than two inches over two days from California Oregon Washngton Canada Decreasing Trend Increasing Trend

Trend in the top 60 storms: 24h rainfall

High Resolution Global Warming Simulations: Looking to the Future

Its Not So Simple Flooding is associated patterns called “Atmospheric Rivers”….a.k.a. the Pineapple Express…which are closely associated with the the jet stream.

Another possibility Most most models suggest the jet stream will weaken and move poleward under global warming. Will the “hose”---the atmospheric rivers move with it? Is that is what is happening in Oregon? A lot of uncertainty exists.

What about other weather elements influencing the parks? Major Northwest windstorms…like the Columbus Day Storm or the Chanukah Eve Storm…are closely associated with the jet stream. Unlike hurricanes their energy source is horizontal temperature contrasts, not warm water. Climate models suggest that the jet stream…and associated temperature contrasts, will weaken and more northward. Implication: weaker and farther north storms in the midlatitudes Interestingly, the number of major windstorms in Oregon has apparently decreased.

Declining snowpack due to global warming? Major issue in the popular threat and among some politicians—some claiming we have already lost 50%! From Mote et al 2006

Washington-wide snowpack since 1950, Relative to normal Snowpack in usual maximum month

Washington-wide snowpack period of record, Relative to normal Snowpack in usual maximum month

Stoelinga et al Time series of elevation quartile (EQ)-averaged 1 April SWE (in mm) measured at snow course during the period Elevation ranges for the four quartiles are: (1) m; (2) m; (3) m; and (4) m. Dashed lines show best-fit lines for each EQ. Also listed are the trends for each EQ (as percent of the mean). EQ1 EQ2 EQ3 EQ Trends in 1 Apr SWE for Elevation Quartiles (EQs): EQ4: +7.1% EQ3: +9.4% EQ2: +7.8% EQ1: +6.4% Cascade Snowpack has INCREASED during the past 30 yrs Low High

Pacific Decadal Oscillation (PDO) PDO is thought to be a natural mode of atmospheric variability Negative phase of PDO associated with greater snowpack in NW.

A Favored Area? The Northwest is downwind of the eastern Pacific and thus our snowpack is controlled by the Pacific temperatures. The eastern Pacific has not warmed up during the past 30 years. Global climate models suggest the eastern Pacific will warm more slowly than most locations.

Change in Surface Air Temperature (°C) from Air Temperature Trend ( )

Climate Model Output for 2100

Stoelinga, Albright and Mass 2008 Predicted linear trend of November-March mean temperature for 2000 to 2025 (°C), as predicted by the ensemble of climate models used in the IPCC AR4 report. Shown are the ensemble means of (a) sea-surface temperature, (b) surface air temperature, and (c) 850-hPa temperature. (a) SST(b) T sfc (c) T °C Averaging a collection of the best climate models over the Pacific Suggests the Same Thing for the Future SST850 mb Air Temp

Summary Global warming is certain, the question is its magnitude and regional effects. The magnitudes of the changes will vary geographically, and the Northwest may see weakened and delayed effects, because of our location downstream of the Pacific, and the nature of our storms. Global warming is a serious, but complicated issue, and some of the ideas being thrown around by the popular press and well-intentioned but misinformed people are not necessarily correct. Little concrete evidence at this time of any major global warming threats to the region or the parks during the next several decades