Lakes occur across the globe and are sensitive to climatic change. Analysing the sediments that have accumulated at the bottom of lakes over time can help us to reconstruct past environmental change. Here, we focus specifically on the use of oxygen isotopes from lake sediments to reconstruct climate change (Fig.1). What are isotopes? Isotopes are variations of a particular chemical element. It is all to do with the number of neutrons. Oxygen has two main isotopes: 18O which has 10 neutrons and 8 protons; and 16O which has 8 neutrons and 8 protons. Although these variants have a different number of neutrons (and therefore a different atomic mass),...