Bacterial tetraether membrane lipids in peat and coal: Testing the MBT-CBT temperature proxy for climate reconstruction

► Temperature reconstructed from peat bogs might be higher than measured temperature. ► Branched tetraether membrane lipids in a peat core are dominantly fossil species. ► Branched tetraethers are well preserved in immature lignite. ► Branched tetraethers disappear in coal with vitrinite reflectance >0.32%. ► There is potential for the MBT-CBT proxy but more work is needed to improve accuracy.