Glaciers of the Olympic Mountains, Washington—The Past and Future 100 Years

Fountain, A. G., C. Gray, B. Glenn, B. Menounos, J. Pflug, and J. L. Riedel (2022), Glaciers of the Olympic Mountains, Washington—The Past and Future 100 Years, J. Geophys. Res..

In 2015, the Olympic Mountains contained 255 glaciers and perennial snowfields totaling 25.34 ± 0.27 km 2, half of the area in 1900, and about 0.75 ± 0.19 km 3 of ice. Since 1980, glaciers shrank at a rate of −0.59 km 2 yr −1 during which time 35 glaciers and 16 perennial snowfields disappeared. Area changes of Blue Glacier, the largest glacier in the study region, was a good proxy for glacier change of the entire region. Modeled glacier mass balance, based on monthly air temperature and precipitation, correlates with glacier area change. The mass balance is highly sensitive to changes in air temperature rather than precipitation, typical of maritime glaciers. In addition to increasing summer melt, warmer winter temperatures changed the phase of precipitation from snow to rain, reducing snow accumulation. Changes in glacier mass balance are highly correlated with the Pacific North American index, a proxy for atmospheric circulation patterns and controls air temperatures along the Pacific Coast of North America. Regime shifts of sea surface temperatures in the North Pacific, reflected in the Pacific Decadal Oscillation (PDO), trigger shifts in the trend of glacier mass balance. Negative (“cool”) phases of the PDO are associated with glacier stability or slight mass gain whereas positive (“warm”) phases are associated with mass loss and glacier retreat. Over the past century the overall retreat is due to warming air temperatures, +0.7°C in winter and +0.3°C in summer. The glaciers in the Olympic Mountains are expected to largely disappear by 2070. Plain Language Summary The Olympic Mountains in Washington State contain 255 glaciers and perennial snowfields as of 2015. Their total area is 25.34 ± 0.27 km 2, about half of the ice-covered area in 1900. Since 1980, yearly glacier area loss averaged −0.59 km 2 yr −1 and 35 glaciers and 16 perennial snowfields have disappeared. Warming winter temperatures are particularly important to the glacier shrinkage. Because the Olympic Mountains are close to the Pacific Ocean winters are mild and air temperatures are close to freezing. Warming winters causes more precipitation to fall as rain rather than snow, which does not nourish the glaciers. With warmer summers causing more ice melt and warmer winters causing less snowfall, the glaciers are being hammered in both seasons. Local air temperatures, and therefore the glaciers, are strongly affected by surface temperature of the nearby ocean. The future of these glaciers is dire, modeling using climate projections suggests that the glaciers will largely disappear by 2070.