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The first Rio Earth Summit in 1992 marked a heady period for environmentalists – Mother Earth had been declared TIME’s Person of Year, and the largest gathering of heads of state ever in the Earth’s history converged on Rio to put their signatures on new treaties to protect biodiversity and control climate change, and to draft global guidelines for forest conservation and human development. I had just helped to start Conservation International after leading The Nature Conservancy’s international program. There was a sense that we’d arrived. Finally, finally, after decades toiling in our rabbit holes, pushing for change on a global scale, we were taking a giant leap forward. I left the conference buoyed.

But what I remember just as vividly now was a moment near the end of the summit when I found myself next to then-Sen. Albert Gore. Could we live up to these bold promises back home? I asked him.  “I don’t think so,” he said.

He was right, of course. The last two decades have seen the United States abdicating leadership on climate change, and the world hurtling toward dangerous and chaotic environmental tipping points.