As climate warms, melting mountain glaciers are likely to contribute significantly to sea level rise over the next decades, but how much they will contribute remains uncertain, as the total volume of Earth's mountain glaciers is not precisely known. Some studies have estimated the total volume of water stored in glaciers worldwide using statistical techniques, but these studies do not take into account features of individual glaciers such as surface geometry and local climate. Other studies have used physically based methods to calculate ice thickness for small numbers of glaciers, but a worldwide, physically based study has not been done until now.