1980s

In 1979, satellites began continuous measurement of Arctic sea ice for the first time, and the September extent they recorded across that opening era, 6.85 million square kilometers averaged from 1979 through 1992, became the baseline against which every subsequent measurement would be read, though at the time it was simply the amount of frozen ocean that survived each summer, a physical quantity requiring no interpretive frame because no frame had yet been built around it. At Mauna Loa Observatory, where Charles David Keeling had tracked atmospheric carbon dioxide since 1958, the concentration at the decade's start stood near 339 parts per million, rising at roughly 1.6 ppm per year, double the rate of the 1960s. By 1989 it would reach 353. Across a single decade the Keeling Curve's rise still looked gradual, its seasonal oscillations regular as breathing, each spring drawdown and autumn release fitting inside the one before.

Above Antarctica, the ozone column was thinning through thresholds no one had known existed. Total column ozone, never observed below 220 Dobson Units before 1979, dropped to 173 DU in 1982, 154 in 1983, 124 in 1985. When Farman, Gardiner, and Shanklin published their ground measurements in Nature on May 16, 1985, NASA went back to its own satellite archive and found the same collapse already there, years of it, sorted into an error bin. The algorithms had rejected the readings. The numbers fell outside the range the software recognized as physically possible. By the decade's end the hole was still growing, and the instruments kept recording what the system had not yet learned to believe.

1990s

On June 15, 1991, Mount Pinatubo ejected 20 million tons of sulfur dioxide into the stratosphere. Northern Hemisphere temperatures dropped 0.5 to 0.6°C. The aerosols dispersed. Warming resumed. By 1998, El Niño drove the first mass bleaching ever recorded on the Great Barrier Reef: symbiotic algae expelled from coral tissue, calcium carbonate skeletons exposed to open water, 16 percent of reef-building corals killed. Nothing in 500 years of growth record showed precedent. Arctic September ice averaged 6.46 million square kilometers. Down from 6.85. In 1992, the TOPEX/Poseidon satellite began measuring global sea level from orbit. Another baseline being set.

2000s

September 2007: Arctic ice fell to 4.28 million square kilometers, thirty-nine percent below average. The Northwest Passage opened. Greenland and Antarctica shed a combined 475 gigatons per year, accelerating. West Antarctic loss: sixfold since the early 1990s. Ocean pH down 0.1 units, 30 percent more acidic, the same calcium carbonate that builds reef skeletons now harder to form. CO₂ at Mauna Loa: 387 ppm.

2010s

Arctic ice: 3.39 million square kilometers, September 2012. Half the 1980s baseline. CO₂ passed 400 ppm. Sea level: 3.6 mm/year, two and a half times the twentieth-century rate. Great Barrier Reef bleached in 2016, again in 2017. Growth rate: 2.6 ppm/year.

2020s

423.9 ppm. Largest annual increase on record. Arctic winter maximum: record low, second consecutive year. Colorado snowpack: lowest since 1981. March 2026: 112°F at four Southwest stations, eight hundred times more likely. Warming accelerating since 2015. Plants absorbing less CO₂ than models assumed. The instruments keep recording.