I watched it live the other day, and I knew Mr Grantham is considered a 'perma-bear' by many, but the interview was pretty depressing for the long term from my POV - appropriate thread title ha.
He did say they don't see any short term issues with the US/global economy or markets.
At the same time, some of his major longer term concerns seem well founded if we (globally) don't change our ways. Without some changes in human behavior and/or some technological breakthroughs, we could get into trouble with population, climate change, food, energy, water, etc. That said, technological breakthroughs have prevented past issues over and over (as Charlie Rose pointed out), and we'd all like to believe it will happen again and again, as it has in the past.
But when Jeremy Grantham starts talking about bubbles again, his timing may be off, but his track record seeing them coming appears to be pretty good. Might be worth considering when he gets alarmed again. Stay tuned?