Land ice tracker: glaciers, Greenland and Antarctica

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Interpretation

The GRACE (2002–2017) and GRACE Follow-On (since 2018) satellites measure tiny changes in Earth's gravity; less ice means slightly less pull. The values are mass changes in gigatons (1 Gt = 1 billion metric tons, about 1 km³ of water), shown here relative to the first 12 months of the record. Between the two missions there is a gap of about a year (mid-2017 to mid-2018). Sea-level equivalent: 362 Gt of ice spread over the world's oceans raises sea level by about 1 mm. Gaps: the original GRACE satellites lost battery capacity from 2011, so they were switched off for a month or two every few months to save power; the mission ended in 2017 and its successor, GRACE-FO, started delivering data in mid-2018, with a few more months missing in its first months. Lines are broken across gaps of more than about three months. Yearly change = the average of one year minus the average of the year before; for this, gaps of up to three months are filled by straight-line interpolation, and only years with at least ten months count. Glaciers (all glaciers outside the two ice sheets, mostly in mountains and the Arctic): yearly mass change per hydrological year (October to September in the north; labeled by the year it ends in), from the World Glacier Monitoring Service's gridded product on the Copernicus Climate Data Store, which combines field measurements with satellite elevation changes (doi:10.24381/cds.ba597449). Its uncertainty is shown in the tooltip. In the sea-level chart, glaciers are added up from 2002–03 onwards and the ice sheets are read off at the end of each September, so all three start at about the same time. GRACE measures the whole of Greenland and Antarctica, including the separate glaciers around their edges, so in that chart those glaciers count with Greenland and Antarctica, and the glacier bar shows only the other glaciers; otherwise they would be counted twice. Data: NASA JPL GRACE/GRACE-FO mascon time series, release 06.3 version 04: Greenland (doi:10.5067/TEMSC-GT634) and Antarctica (doi:10.5067/TEMSC-AT634).

Greenland's summit over 4,000 years

Summit is the highest point of the Greenland ice sheet, about 3,200 m up; the GISP2 ice core was drilled 30 km to its west. Temperatures here are far below zero all year. Blue line: snow temperature at the drill site reconstructed by Kobashi et al. (2011) from argon and nitrogen isotopes in the air bubbles trapped in the ice; these respond to temperature changes at the surface, and the method gives one value a year, smoothed over a decade or more. Shaded: its 1-sigma uncertainty. The record ends in 1950. Red: measured since 1940, ERA5 yearly mean air temperature 2 m above the snow in the 2-degree grid cell that contains Summit (dots: single years; line: 10-year average). Air and snow temperature are not the same, and ERA5's grid cell is a little lower and warmer than the summit, so the red series is shifted to the ice-core scale: by °C, so that its 2001–2010 average equals the −29.9 °C that Kobashi et al. give for the drill site for that decade. Only the ups and downs of ERA5 are used, not its level. Over the years where both exist (1940–1950) the two differ by °C on average; ERA5's early decades over the middle of the ice sheet are less certain, because there were hardly any measurements to feed it. Second chart: the oxygen-isotope temperature record of Alley (2000) from the same core, as published; its ages count back from 1950, and the youngest value is about 95 years before 1950. Data: Kobashi, T., et al., 2011, High variability of Greenland surface temperature over the past 4000 years estimated from trapped air in an ice core, Geophys. Res. Lett. 38, L21501 (doi:10.1029/2011GL049444); Alley, R.B., 2000, The Younger Dryas cold interval as viewed from central Greenland, Quat. Sci. Rev. 19, 213–226 (doi:10.1016/S0277-3791(99)00062-1); both via NOAA's World Data Service for Paleoclimatology (Kobashi, Alley). ERA5: Copernicus Climate Change Service, monthly averaged data on single levels (doi:10.24381/cds.f17050d7), yearly averages calculated by this site.