Sustainability has become center stage in the minds of many investors around the world. Perhaps the most important issue facing the world related to sustainability is how sustainable the current world order is.

Right now, the U.S. national debt is estimated to be about $22 trillion. With a population of approximately 326.8 million, that equates to roughly $77,526 per capita — for a family of four, $310,104 per family. That’s equivalent to 5.49 times the median U.S. household income of $56,516.

The growth in the debt has been staggering. In 1929, on the eve of the Great Depression, the national debt hovered around $17 billion and accounted for 17 percent of GDP.

By the time the United States entered World War II in 1941, it had nearly tripled, to $49 billion, roughly 45 percent of GDP.

By the year I was born, in 1951, it had grown fivefold to $255 billion, or 74 percent of GDP.

By the time I turned 50, it had doubled again to $580 billion, or 55