Freezing Level Height in the Western Equatorial Pacific over the Last 200 Years: Glacier Evidence from Mt. Jayawijaya, Papua Province, Indonesia

The temperature and moisture history of the equatorial lower free troposphere over the last few hundred years is important for evaluating and predicting global warming. New evidence constrains the freezing level height (FLH) in the western equatorial Pacific over the last 200 years using the snow-line altitude (ELA) on glaciers at elevations of 4000 to 5000 m (600 hPa) on Mt. Jayawijaya, Papua Province, Indonesia (4oS, 136oE). The ELA of these wet tropical glaciers is closely coupled to the mean annual 0oC isotherm. The areal recession of the Jayawijaya glaciers continued to May 2011 by which time 95 percent of the ice cover that existed between 1936 and 1942 disappeared; 1 km2 remained. For the periods 2000-2006 and 2006-2011, the ELA was above 4950 m above sea level (asl). Revised reconstructions of the glaciers from 1936 to 1942 based on aerial photographs indicate that the concurrent ELA was at 4610 ± 10 m asl. The glaciers were interpreted to be in mass balance equilibrium between 1936 and 1942 because no appreciable areal change was detected and the glacier fronts had steep profiles. We assumed an accumulation area ratio of 0.8, typical of tropical glaciers. Extensive, fresh moraines downvalley from the 1936 ice margin indicate that the glaciers were more extensive and had lower ELAs in recent centuries. We define the most extensive, fresh moraine system of the Jayawijaya glaciers as representing the local Little Ice Age (LLIA) maximum and, following previous work, assign its age as ~1850. Our reconstruction of the Jayawijaya glaciers at the LLIA maximum based on moraines and current topographic divides indicates that they covered an area of 30 km2, considerably more than previous estimates. A concurrent ELA at ~4450 m asl was calculated assuming an accumulation area ratio of 0.8. The moraines indicate that the glaciers were in equilibrium. Taken together, glacier ELAs on Mt. Jayawijaya, approximating the FLH, have risen 500 m since the LLIA maximum. The average ELA and FLH rose at ~100 m/decade from 1972 to 2005, after which they exceeded 4950 m. For 125 years before 1972, the ELA rose on average at less than 20 m/decade. We seek a link between the rise in FLH, atmospheric warming, and western Pacific sea-surface temperature change.