By "Clean Air" are you referring to the "Clean Power Plan"?
To make it clear, Obama came up with a set of regulations he called the "Clean Power Plan." But they were only regulations, not a law. And to be valid regulations, they have to be based on an underlying law. In this case, the underlying law on which they were supposedly based was the Clean Air Act. The Supreme Court rejected that, and said that Obama's Clean Power Plan exceeded the EPA's authority under the Clean Air Act. The President can sign whatever Agreements he wants -- the Constitution doesn't prevent that. In fact, there is a pretty long history of U.S. President's signing international agreements without the consent or approval of the Senate. The Treaty of Versailles, for example. President signed it, Senate never ratified it, so it was never U.S. law.. Same with the Kyoto Protocol. Clinton signed it, Senate didn't ratify it, so it was unenforceable.
Obama just did the same with the Paris Agreement, which even by its own terms has no enforceable provisions even if ratified. The joke is that countries realized they'd have a hard time getting the agreement of their people/legislatures, so they deliberately designed the Paris Agreement to not be a treaty anyway.
So, the Agreement that Obama signed has no direct relationship at all with the Supreme Court's hold on the Clean Power Plan. If someone says it does, they don't know what they're talking about.
Sounds like I asked the right person! Thank you for straightening that out for me. I did find it rather curious that such an action as described by the author of that article could have happened without causing a “ripple”. You have sorted it out for me and I can now stop dwelling on it.