HEADLINES FROM 1942: Young woman visiting Paris receives number tattooed on arm: “Why I left the Paris Climate Summit with an activist tattoo.”

I never imagined I would get a tattoo during the U.N. Climate Summit in Paris. Yet here it is, newly healed and permanently inked on the inside of my right wrist.

The tattoo is three numbers and a symbol: “355<” in 25-point font, styled as if from a typewriter. It’s my commitment to the people of the climate movement, to listening to and sharing their stories of climate justice.

When I was born in October 1991, the concentration of carbon dioxide — the primary greenhouse gas emitted by human activity — in our atmosphere was 355 parts per million. In the early 20th century, we topped 300 ppm for the first time in 800,000 years, beginning the destabilization of our climate and society through rising planetary temperatures.

I never knew these exact numbers before, but now that they’re printed on my wrist, I will never forget.

Huh — in the past, a lot of people with numbers tattooed on their arms uttered those last two words.