U.S. President Barack Obama put on a cheerful face before he climbed aboard Air Force One to go home from the Group of 20 summit in Brisbane. He chortled that the summit "wasn't just a good old chin wag, I really love that expression." He listed achievements on the economy and trade, climate change and Ebola, and boasted that the meeting had promoted "historic steps toward a cleaner and healthier planet."

Far be it from me to accuse the president of the most powerful country on Earth of wishful thinking, but he is stretching the facts and ignoring some difficult home truths — which are that this battered and fragile planet needs something better than an alphabet soup of summits to sustain it. We are in more perilous times than Obama or any other leader admits or has solutions for. Underneath the claims to have agreed on 800 measures to inject $2.1 trillion to global growth by 2018 and to clean up the planet, disagreements among leaders about the way to go imperil all our futures.

The G-20 claims to "represent over 85 percent of the global economy". But real power lies — dangerously — with national government heads who could hardly give a damn about the rest of the world. Look what happened at Brisbane. The city's pleasant center became a "red zone" and locked down, "zombiefied" as one local commentator put it. At the University of Queensland, where Obama made a speech, police declared a special security zone with invitation-only guests were banned from wearing masks or carrying eggs.