The Shifted Baseline

Scientists measure temperature anomalies: the gap between what's happening and a historical average. The baseline. The zero line on the chart. The definition of normal against which abnormal gets measured.

Here's the problem with baselines: they move.

The World Meteorological Organization updates its reference period every thirty years. Currently we compare against 1991–2020. Before that, 1981–2010. Each update incorporates newer, warmer years. The reference point rises. The anomaly appears smaller. The underlying reality stays in the same absolute place; the perception of it drifts.

What was once a catastrophic anomaly becomes the floor. The next record is measured against the previous record. The math quietly normalizes the abnormal.

June 2023: ocean surfaces at 0.9°C above the 1991–2020 average. Except that 1991–2020 average was already warmer than the 1961–1990 average. Which was already warmer than the pre-industrial world. The anomaly is an anomaly inside an anomaly.

The chart looks comprehensible. The underlying situation is not.

This is shifting baseline syndrome, applied in real time. The term comes from fisheries science: each generation of researchers accepted the fish stocks of their own youth as the natural state, and so the collapse never looked like a collapse — just a series of small adjustments to normal. The ocean is now running the same experiment on all of us, at planetary scale, with a thirty-year refresh cycle.

The instruments are honest. The framing is not. A 0.9°C anomaly against a moving reference sounds manageable; the same water measured against the world the instruments were built in does not. Nothing in the data hides this — you can chain the reference periods back and recover the full displacement. But nobody reads charts that way. We read the anomaly, nod at the zero line, and the zero line was redrawn while we were not looking.

June 2023 was not an aberration that passed. It was the month the floor moved up to meet the spike — and the next record will be measured from there.

The baseline shifted. The water did not ask which average we were using.