Bank of England Governor Mark Carney says easier monetary policy may be needed to help a slowing economy in the wake of the U.K.'s vote to leave the European Union. This response is straight from the handbook of modern central banking—a favorite with the Federal Reserve, the Bank of Japan, and just about every other central bank. But it might be the wrong reaction.

I argued last month that ever-lower interest rates might be destroying whatever faith businesses and consumers have left in the economic outlook. Cheap money keeps zombie companies alive, trapping capital in unproductive endeavors that would otherwise die. And negative interest rates are unprecedented, and look a lot like allowing doctors to experiment on their patients. The feedback I got suggested another compelling reason that higher rates might be a better approach: demographics.

If you look at the age balance of the global population between old and young people, the over-65s account for almost 9 percent of the total, a figure that's been rising steadily and has doubled since the start of the last decade. For the euro region, this cohort accounts for closer to 18 percent; in the U.S., more than 15 percent of the population is past standard retirement age, up from 12.5 percent a decade ago.