On the eve of the 1972 United Nations Conference on the Human Environment in Stockholm, a group of 2,200 scientists signed a letter — now known as the Menton Message — to their (then) 3.5 billion neighbours on Earth. In one of the earliest examples of researchers collectively calling for societal change, they sounded the alarm on the ongoing environmental crisis, the nuclear arms race and the possibility of the extinction of life on Earth. As the Stockholm+50 summit gets under way this week — the UN conference’s 50th anniversary — the International Science Council, Future Earth and the Stockholm Environment Institute have convened an expert group of natural scientists, social scientists, engineers and humanities scholars to modernize and extend that historical call. Writing as co-chairs of that group, we invite readers to sign our open letter at https://science4stockholm50.world.