World leaders converged at United Nations headquarters in New York on Friday — Earth Day — to sign the historic Paris climate accord.

The U.S. and China, which together account for nearly 40% of global emissions, have said they intend to formally join the agreement this year, according to the Associated Press. Both nations' leaders signed the document Friday.

"The United States is looking forward to joining the Paris Agreement this year, and we invite our partners to do the same," said U.S. Secretary of State John Kerry, who held his young granddaughter as he inked his name on the pact.

The Paris Agreement is certainly a treaty. I reviewed enough treaties during my time in the Senate where I served on the Foreign Relations Committee to know. But don't take my word for it. The State Department's internal guidelines make clear that the Paris Agreement is a treaty.

Those guidelines, known as the Circular 175T procedure, demonstrate that the Paris Agreement is a treaty. For example, the Agreement makes environmental commitments that affect the U.S. as a whole. The Agreement is formal and complex rather than informal and routine. The Agreement is open-ended and requires the U.S. to deliver untold billions of dollars to a "Green Climate Fund" for redistribution around the world to pay for "green projects" in foreign countries. These all indicate that the Agreement is a treaty and not a mere executive agreement, as the president claims.