With regard to global warming, an understanding of past temperature changes is becoming increasingly important. Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are membrane lipids used globally to reconstruct lake water temperatures. In the Bale Mountains lakes, we find a unique composition of brGDGT isomers. We present a modified local calibration and a new high-altitude temperature reconstruction from the Horn of Africa spanning the last 12.5 kyr.