Lidar measurements of the worldwide movement of stratospheric aerosols produced by the 18 May 1930 eruption of Mount St. Helens are described. Ground-based and airborne measurements show that the layers below 20 km produced by this eruption moved in an easterly direction while those above 20 km moved in a westerly direction. The effluent at jet stream altitudes of 10-12 km circled the globe in about 16 days, and the effluent at 23 km (the highest altitude recorded) circled the globe in about 56 days. Mass calcu-lations, using backscatter-to-mass conversion models, indicate that approximately 0.5 x 106 metric tons of new stratospheric material was produced by this eruption. Even though this represents a 2008 increase in Northern Hemispheric aerosol, no significant long-term atmospheric temperature change should occur.