"Near the moonscape summit of the Mauna Loa volcano in Hawaii, an infrared analyser will soon make history," reports Richard Monastersky in the international science journal, Nature.
"Sometime in the next month, it is expected to record a daily concentration of carbon dioxide in the atmosphere of more than 400 parts per million (p.p.m.), a value not reached at this key surveillance point for a few million years."
It's not as if anything earthshaking will happen. But it's nevertheless considered a point at which climate change will more or less have its own momentum.
"It will be a while, perhaps a few years, before the global CO2 concentration averaged over an entire year, passes 400 p.p.m.. But topping that value at Mauna Loa is significant because researchers have been monitoring the gas there since 1958, longer than any other spot," Monastersky writes in a fascinating article.