A Global Meteoric Water Line (GMWL) is used to measure how much water is in the atmosphere around the world. The GMWL is a line that goes around the world and connects all the locations where scientists measure the amount of water in the atmosphere. This line is important because it helps scientists understand how much water is in different parts of the world. It also helps them understand how much water is changing over time. Scientists use the GMWL to learn about climate change and how much moisture is in the air, which is important for predicting weather patterns.