Amplified temperature change at high elevation in the tropics during the LGM

Mountainous regions are currently experiencing warming at a faster rate than the global average. Evidence for how these regions changed during the past is essential for calibrating models and predicting future changes. Here we present temperature reconstructions for high-elevation regions in tropical East Africa during the LGM from two independent proxies. One temperature reconstruction is based on well-dated past glacial extents combined with glacial modeling to estimate a range of climate conditions in the Rwenzori Mountains. The other is based on measurements of brGDGTs in lake sediments from the Rwenzori Mountains and Mt. Kenya. Results from both proxies indicate cold conditions during the LGM in these high-elevation regions. Modeling of Rwenzori glaciers requires a lapse rate steeper than modern in order to reproduce LGM glacial extents, assuming reasonable temperature and precipitation values. A new temperature reconstruction from Lake Mahoma in the Rwenzori Mountains agrees well with that from a similar-elevation lake on Mt. Kenya, supporting the interpretation of a steepened LGM lapse rate (Loomis et al., 2017). These new data reinforce prior work indicating a mismatch between data-model comparisons of high-elevation tropical temperatures during the LGM, specifically that modeling efforts (e.g., CMIP5/PMIP3) underestimate the temperature change and, thus, the lapse rate. The results presented here provide important targets for LGM climate conditions in the tropics and have implications for projecting future changes in these mountainous regions.