Sea-level rise is governed by three factors: melting of permanent snow cover and mountain glaciers, the thermal expansion component of sea level, and decreases in the size of permanent ice sheets, the last of which is the least well constrained. The measurements proposed for ICESat-II directly address the contribution of changing terrestrial ice cover to global sea level. Thus, they are key to projecting the effects of sea-level change on growing populations and infrastructure along almost all coastal regions.

Canopy-depth measurements made from ICESat-II will address changes in terrestrial biomass, which stores a substantial amount of carbon. Many factors influence the character of the vegetation, including climate, land-use, and fertilization by increased CO₂. Measurement of the vegetation-canopy depth will contribute to the ability to assess those influences and therefore better understand the carbon balance and future climate change.

Background: Space-borne lidar is a demonstrated technology for obtaining highly accurate topographic measurements of glaciers, ice sheets, and sea ice. Repeated observations of the polar ice caps by NASA’s