The State Department’s top climate change diplomat says next week’s United Nations green development conference in Brazil is a high priority for U.S. officials even though President Obama isn’t showing up.

Heads of state from over 100 nations are slated to attend the June 20-22 United Nations Conference on Sustainable Development in Rio de Janeiro. Secretary of State Hillary Clinton, not Obama, is heading the U.S. team, disappointing some environmentalists.

But Todd Stern, the State Department’s special envoy for climate change, noted Friday that not every nation is sending its head-of-state.