The quiet arithmetic of a warming year.
On reading the small numbers that, when summed, become a planetary signal.
Every climatology begins with a column of numbers. Not a photograph of a melting glacier, not a satellite mosaic of a burning forest — a column. Each row is a year, each cell a deviation from some agreed-upon mean, and the apparatus of modern climate science is, at base, the patient accumulation of these deviations until a pattern declines to be ignored1.
By April of 2024, the column had grown long enough to read as prose. The previous twelve months registered the warmest interval in the instrumental record, surpassing 2016 by a margin large enough that the statisticians no longer quibble2.
The interesting question is no longer whether the planet is warming but where the heat is travelling. In the North Atlantic, sea-surface temperatures held three standard deviations above the climatological mean for the better part of a year — a deviation whose probability, under stationary assumptions, is so small as to be effectively a refutation of stationarity itself3.
South of the Sahel, the rains were both fewer and more violent. The Horn of Africa, after five failed wet seasons, received in March the rainfall of a usual year, much of it within seventy-two hours.
There is a temptation, in writing of these matters, to reach for adjectives. The data does not require them. A river that has lost a third of its discharge has lost a third of its discharge; the word unprecedented adds nothing the number had not already supplied.
And yet the reader is owed, occasionally, an image — not as ornament, but as referent. The photograph at right was taken in the lower Tigris basin in September, sixty kilometers from a town whose well failed in July.
Precipitation, the second of our two indicators, behaves less politely than temperature. Its anomalies are noisier, its trends slower to certify. Still, the regional small multiples on the preceding page repay a moment of close reading. Note the synchronous downturn across the Mediterranean basin and the Iberian peninsula; note the equally striking surplus across maritime South-east Asia.
The mean global precipitation has, of course, not changed; water is conserved. What has changed is its distribution — and distribution, not total, is what agriculture is built upon4.
We end, as we began, with a column. The reader who has followed this issue carefully will have absorbed perhaps forty small numbers. That, in the present discipline, is more than most editorials offer in a year — and considerably more, we suspect, than is comfortable. The discomfort is the point.
— E.M.