His argument is that sometime in the next 275 years we have to make some change to our economic system, unless economic growth decouples from energy use growth during that time.
What he doesn't say is that it has been decoupling for decades even before he wrote that post, and, by an equally valid extrapolation argument, economic growth will become completely decoupled from energy use globally in another 50 years:
https://ourworldindata.org/grapher/energy-intensity-of-econo...