Paleoclimatic evidence that can be used to indirectly infer or estimate some aspect of the paleoenvironment, such as precipitation or temperature. Temperature proxies such as tree ring widths and ice core layering are used by paleoclimatologists to create a past temperature record. Tree ring widths can also be used to infer precipitation changes. Isotopic variations in ice cores can be used to infer temperature changes and ice sheet volume. Beryllium 10 variations can be used to infer past solar irradiance .