Paul Krugman is a very well rounded and balanced economist, he knows when the invisible hand works and when it does not, but he, as many economists, believe that growth is not part of the environmental problem. I suggest you invite some ecological economist like Herman Daly or Giogios Kalis. Regarding the "productivity stagnation", I think someone should consider the open source economy, as many of the current value is for free and hence not considered in GDP, hence giving the impression of stagnation. The numbers of hours works are going down, and this should be explained greatly by AI.