Sea Change- Mountains, oddly, are the reason most of us have learned to think of the level of the sea as a stable point, a baseline, an unmoving benchmark against which one might reasonably measure the height of great peaks.

In 2019, a plaque was erected to commemorate the first glacier in Iceland to shrink so much that it could no longer be considered a glacier. Like the tsunami stones of the past, the plaque carried a message for the future, a warning to believe in changes that might at first seem implausible. It also carried a recognition of responsibility. “In the next 200 years all our glaciers are expected to follow the same path,” the plaque reads. “This monument is to acknowledge that we know what is happening and what needs to be done. Only you know if we did it.”

- By Brooke Jarvis - Illustration by Alexander Glandier

In the mid-fifteen-hundreds, a Swedish peasant named Nils lived on an island called Iggön in the Baltic Sea. He was known to his neighbors as Rich Nils, apparently because of the plenitude of fish in the waters near his home and, even more lucrative, the seals that showed up to hunt them. There was one rock in particular where seals liked to haul themselves out of the ocean to rest and bask in the sun. Nils, for his part, liked to visit this rock with his harpoon.

Eventually, though, Nils noticed that the seals had begun gathering on a lower part of the rock, rather than on the high point, as they once did. It seemed that the water level no longer gave them access to the very top. This was a troubling development for Rich Nils’s income: the high point now obstructed the path of his harpoon when he approached the rock from the shore. Nils used fire to weaken the rock, chipping away at it until he’d not only removed the high point but also lowered the over-all height of the rock, so that seals would be able to rest on it even when the sea reached its lowest level of the year.

Some hundred and eighty years later, the Swedish physicist and mathematician Anders Celsius went looking for Rich Nils’s rock. Celsius was known for his obsession with quantifying the world around him; he tried to calculate the distance between the Earth and the sun, was involved in the long quest to use meridian measurements to determine the size and shape of the Earth, and famously proposed a new scale for gauging temperature. Now he was once again in search of a way to measure what had previously been unmeasurable.