Thirty years ago, as the atmosphere’s protective ozone layer was dwindling at alarming rates, we were serving proudly under President Ronald Reagan. We remember his leading role in negotiating the Montreal Protocol, which continues to protect and restore the delicate ozone layer. Today the world faces a similar challenge: the threat of climate change.

Just as in the 1980s, there is mounting evidence of problems with the atmosphere that are growing too compelling to ignore. And, once again, there is uncertainty about what lies...