As President Joe Biden moves quickly to reinstate the full slate of environmental policies weakened by former President Donald Trump, including the landmark Migratory Bird Treaty Act, he’s signaling that climate change and biodiversity loss are now major priorities for the US.

Earlier this month, the Interior Department also launched a campaign to conserve 30 percent of US land and water by 2030, joining more than 50 other countries that have committed to that goal. Biden is pursuing the target, known as 30 by 30, alongside a new and more ambitious commitment to cut carbon dioxide emissions.

Yet there’s one big problem with this post-Trump environmental renaissance: The US still hasn’t joined the most important international agreement to conserve biodiversity, known as the Convention on Biological Diversity (CBD). And it isn’t just a small, inconsequential treaty. Designed to protect species, ecosystems, and genetic diversity, the treaty has been ratified by every other country or territory aside from the Holy See. Among other achievements, CBD has pushed countries to create national biodiversity strategies and to expand their networks of protected areas.

Since the early 1990s — when CBD was drafted, with input from the US — Republican lawmakers have blocked […]