At the global biodiversity talks underway in Cali, Colombia, government officials from a single nation wear badges with a red streak along the bottom emblazoned with a small but jarring word: “non-party.”

Call it a diplomatic scarlet letter.

That country is the United States. The only other delegation with the same status is the Holy See. All the other country delegates saunter around the conference with badges that sport an inviting green line with the word “party,” granting them access to rooms where the most sensitive negotiations take place.

When I started covering biodiversity a few years ago, I was surprised to learn that the U.S. wasn’t a member of the treaty that underpins global agreements on the issue. The absence seemed especially significant given the scale of the problem: a decline in global biodiversity that’s unprecedented in human history, threatening not only countless species but the well-being of humans, too.

I quickly came to understand that the U.S. government does indeed participate in U.N. biodiversity talks, and in significant ways. It sends a delegation. It gives hundreds of millions of dollars in biodiversity funding to other countries. And, of course, it takes its own actions to conserve nature. But when decisions are being made at the global talks, the United States is relegated to the diplomatic sidelines along with other observers like advocacy and business groups.

“Of course we would love to have them as a party,” said Astrid Schomaker, executive secretary of the treaty, which is called the Convention on Biodiversity. “But the U.S. is here.”

It started differently. In the 1980s, the U.S. played a significant role in drafting and negotiating the biodiversity treaty. The first President George Bush declined to sign it, but President Bill Clinton did in 1993. The next step was ratification, which requires two-thirds approval by the Senate. Republicans, led by Jesse Helms and Bob Dole, opposed it amid concerns over national sovereignty and intellectual property. Democrats said those fears were unfounded, but U.S. ratification has been a long shot ever since.