Hoping to kick-start European economies, the European Central Bank took the extraordinary step two years ago of lowering one of its key interest rates to below zero. The idea was to discourage banks from stashing their money in the central bank by charging them a modest rate for doing so. Since the banks would lose money rather than earn interest on their deposits, it was hoped they would be prompted instead to make more loans at lower rates to businesses and consumers.

It hasn’t worked very well. As many experts predicted at the time, the policy has had only a modest impact on growth. It is also increasingly clear that pushing rates down further wouldn’t help much and could, in fact, increase risks to the global financial system.

The European Central Bank, or E.C.B., sets monetary policy for the 19 countries that use the euro. In June 2014 it became the world’s first major central bank to adopt so-called negative interest rates. Monetary officials in Denmark, Switzerland and Sweden adopted similar policies in the following months; the Bank of Japan joined them in January.

Negative rates have helped to push down the cost of borrowing, but that has not provided a big lift to the euro area. The E.C.B. expects growth of 1.6 percent this year, about the same as last year. This is not surprising, because lower rates don’t address the real economic problems of many European countries: weak consumer demand and weak business investment. Companies are less likely to borrow for new investments when demand for their goods and services is not increasing — even if the cost of borrowing is cheaper than ever.