Global mean sea level here is the Church & White (CSIRO) tide-gauge reconstruction, anchored near zero around 1900. It is a reconstruction, not a single instrument, so early decades carry wider uncertainty; satellite altimetry since 1993 shows the rise has accelerated. This series is seed-only — no faithful public live feed is wired yet.

Ocean heat content is NOAA NCEI’s estimate (Levitus et al.) of the heat stored in the upper 700 m of the ocean, in units of 10²² joules relative to the 1955–2006 mean — the clearest single measure of global warming, since the ocean absorbs over 90% of the excess heat. The numbers are abstract but the trend is not: it has climbed from roughly −3 to +23 since 1955.

Sea surface temperature is the Met Office Hadley Centre’s HadSST anomaly — the temperature of the ocean SKIN, vs the 1961–1990 mean. It is a different thing from the heat content above (surface vs the whole upper ocean) and from the land+ocean global anomaly on the Climate page; here it isolates the surface, now warmer (~+1.1 °C) than at any point in the instrumental record. The current year is preliminary.

Arctic sea ice is the September monthly-mean extent from the NSIDC Sea Ice Index (passive-microwave satellites, continuous since 1979). September is the annual minimum — the clearest measure of how much multi-year ice survives the melt season. (This is floating SEA ice; melting it does not itself raise sea level.)

Antarctic sea ice is the annual MINIMUM (February) extent from the same NSIDC record (via OWID). For decades it drifted sideways or even grew slightly, confounding expectations — until 2023, when the summer minimum collapsed to the lowest in the satellite era and has stayed near those lows since. Like the Arctic, this is floating sea ice; its loss removes a bright, reflective surface and exposes dark, heat-absorbing ocean.

Mountain glacier mass is the cumulative mass balance of the WGMS reference glaciers — the ~40 best-monitored glaciers worldwide with 30+ unbroken years of direct field measurement — in metres of water equivalent, served via the Met Office Climate Dashboard. Around 1970 the running balance crossed zero; by 2025 it had fallen to about −28 m w.e., and the recent slope is the steepest in the record. Mountain glaciers matter beyond sea level: roughly two billion people depend on glacier-fed rivers for water.

The Greenland and Antarctica ice-sheet masses are from NASA’s GRACE and GRACE-FO satellites (via OWID), which weigh the ice by sensing its gravity. We show the cumulative change in gigatonnes since 2002 — about −4,900 Gt for Greenland and −2,700 Gt for Antarctica by 2020. Unlike sea ice, this is LAND ice: every tonne that melts adds directly to sea-level rise, and Antarctica holds by far the most.

Ocean pH is surface seawater measured at Station ALOHA in the North Pacific (Hawaii Ocean Time-series, via OWID) — one of the longest open-ocean chemistry records. As the sea absorbs CO₂ it forms carbonic acid; pH has fallen from ~8.11 to ~8.04 since the late 1980s (a pH scale is logarithmic, so that is a ~18% rise in acidity). It is one station, not a global mean, but it tracks the basin-wide trend closely.

All of these are downstream of emissions — warming for sea level and ice, dissolved CO₂ for acidity — so the actions that bend them are the same ones that bend the climate curves.