The response of the Greenland Ice Sheet (GIS) to changes in temperature during the twentieth century remains contentious1, largely owing to difficulties in estimating the spatial and temporal distribution of ice mass changes before 1992, when Greenland-wide observations first became available2. The only previous estimates of change during the twentieth century are based on empirical modelling3, 4, 5 and energy balance modelling6, 7.

In 2002, Munk defined an important enigma of 20th century global mean sea-level (GMSL) rise that has yet to be resolved.

Intensification of the hydrologic cycle is a key dimension of climate change, with substantial impacts on human and natural systems1, 2. A basic measure of hydrologic cycle intensification is the increase in global-mean precipitation per unit surface warming, which varies by a factor of three in current-generation climate models (about 1–3 per cent per kelvin)3, 4, 5. Part of the uncertainty may originate from atmosphere–radiation interactions. As the climate warms, increases in shortwave absorption from atmospheric moistening will suppress the precipitation increase.

Plant photosynthesis and respiration are the largest carbon fluxes between the terrestrial biosphere and the atmosphere, and their parameterizations represent large sources of uncertainty in projections of land carbon uptake in Earth system models (ESMs). The incorporation of temperature acclimation of photosynthesis and foliar respiration, commonly observed processes, into ESMs has been proposed as a way to reduce this uncertainty.

Small glaciers and ice caps respond rapidly to climate variations, and records of their past extent provide information on the natural envelope of past climate variability. Millennial-scale trends in Holocene glacier size are well documented and correspond with changes in Northern Hemisphere summer insolation.

Recent work has suggested that sections of the West Antarctic ice sheet are already rapidly retreating, raising concerns about increased sea-level rise; now, an ice-sheet model is used to simulate the mass loss from the entire Antarctic ice sheet to 2200, suggesting that it could contribute up to 30 cm of sea-level rise by 2100 and 72 cm by 2200, but is unlikely to contribute more.

Methane (CH4) is one of the most important greenhouse gases, and an important energy carrier in biogas and natural gas. Its large-scale emission patterns have been unpredictable and the source and sink distributions are poorly constrained. Remote assessment of CH4 with high sensitivity at a m2 spatial resolution would allow detailed mapping of the near-ground distribution and anthropogenic sources in landscapes but has hitherto not been possible.