Mass balance loss of Mount Baker, Washington glaciers 1990–2010

Abstract Mount Baker, North Cascades, WA, has a current glacierized area of 38.6 km 2 . From 1984 to 2010, the North Cascade Glacier Climate Project has monitored the annual mass balance (Ba), accumulation area ratio (AAR), terminus behaviour and longitudinal profiles of Mount Baker glaciers. The Ba on Rainbow, Easton and Sholes Glaciers from 1990 to 2010 averaged −0.52 m w.e. a −1 (m a −1 ). Terminus observations on nine principal Mount Baker glaciers, 1984–2009, indicate retreat ranging from 240 to 520 m, with a mean of 370 m or 14 m a −1 . AAR observations on Rainbow, Sholes and Easton Glaciers for 1990–2010 indicate a mean AAR of 0.55 and a steady state AAR of 0.65. A comparison of Ba and AAR on these three glaciers yields a relationship that is used in combination with AAR observations made on all Mount Baker glaciers during 7 years to assess Mount Baker glacier mass balance. Utilizing the AAR–Ba relationship for the three glaciers yields a mean Ba of −0.55 m a −1 for the 1990–2010 period, 0.03 m a −1 higher than the measured mean Ba. The mean Ba based on the AAR–Ba relationship for the entire mountain from 1990 to 2010 is −0.57 m a −1 . The product of the mean observed mass balance gradient determined from 11 000 surface mass balance measurements and glacier area in each 100‐m elevation band on Mount Baker yields a Ba of −0.50 m a −1 from 1990–2010 for the entire mountain. The median altitude of the three index glaciers is lower than that of all Mount Baker glaciers. Adjusting the balance gradient for this difference yields a mean Ba of −0.77 m a −1 from 1990 to 2010. All but one estimate converge on a loss of −0.5 m a −1 for Mount Baker from 1990 to 2010. This equates to an 11‐m loss in glacier thickness, 12–20% of the entire 1990 volume of glaciers on Mount Baker. Copyright © 2012 John Wiley & Sons, Ltd.