The National Park Service, United States Geological Survey (USGS) and glaciologists such as Mauri S. Pelto, who has led the North Cascades Glacier Climate Project since 1984, have continued research on North Cascade glaciers. Since 1993, the National Park Service has conducted rigorous studies on four park glaciers: Noisy Creek, Silver, North Klawatti and Sandalee Glaciers. The National Park Service research indicated that these four glaciers experienced rapid decrease in volumes between 1993 and 2011. In 1998, a National Park Service and Portland State University aerial photographic inventory showed a 13 percent loss in park-wide glacial volume since Austin Post's inventory in 1971. The NPS stated that in the last 150 years since the end of the Little Ice Age, a period of several centuries in which the earth experienced a cooling phase, glacial ice volumes in the North Cascades have been reduced by 40 percent. This loss of glacial ice has contributed to decreased melt in the summer. In a paper published in 2016, it was reported that since 1959 the Skagit River watershed has seen a 25 percent reduction in the summertime streamflow.