Important interest rates in Europe and Japan have been negative for several years.The moves, however, could provide a warning about what happenswhen central banks' efforts to support growth create problems instead.That is the idea expressed last week by finance officials and othersat the Reuters Global Investment Outlook 2020 Summit.They argue that the effects of below-zero interest rates are long-lasting and harmful.Interest rates are negative when lenders – not borrowers – must pay interest.Critics say negative rates punish people who save money, cause problems for big banksand lead people to take bigger risks to get a small amount of interest.About $12.5 trillion of the world's bonds,about 30 percent of the debt of countries in the developed world, pay negative interest.The Bank of Japan and the European Central Bank want economic growthand a small amount of inflation, so they have cut their interest rates to below zero.However, a negative interest rate policyhelps keep other interest rates, like the ones banks pay savers, low.That means older people saving for retirement or in retirementare losing money, explained a recent blog post by BlackRock.Blackrock and other investors say the U.S. Federal Reserveunder Chairman Jerome Powell has been closely watching the situation in Europe and Japan.They say Powell wants to avoid negative rates in the United States."When you listen to Powell and other representatives of the Fed,they don't want to takes rates negative," said Dan Ivascyn.He is an investment officer at bond seller Pacific Investment Management Co."It will be well down the list of the tools that they will use," he said.The moves by Europe and Japan's central bankshave raised a question about what tools others,such as the U.S. Federal Reserve, have to fight a slowing economy.The U.S. central bank last month cut its overnight lending rateby a fourth of a percentage pointto a target somewhere between 1.5 percent and 1.75 percent.U.S. President Donald Trump has suggested that the Federal Reservepush interest rates into negative numbers as a wayto permit the U.S. government to refinance its $22 trillion in debt.That is unlikely to happen, some of the financial experts at the meetings said."Never say never, but there is a real hesitancy herein the U.S. to take rates below (zero)," said Greg Peters.He is with the investment company, PGIM Fixed Income."I think the U.S. has had the benefitof seeing the (effects) of negative rates elsewhere," he added.Negative interest rates do not always leadto an increase in lending and growing business investment.Negative rates can cause financial organizations to earn less.If their profits are affected they might stop lending altogetherand that would hurt the economy.Anne Mathias supervises investing at Vanguard.She is an expert in worldwide interest rates.She said negative interest rates are unlikely."If we go into a recession...we will just go back to quantitative easingand expand the balance sheet again," she said.Andrew Hsu is a manager of the DoubleLine Total Return Bond Fund.He warned about the effects of negative rates."If we had negative rates for the next 10-20 years...no one in this room will be able to retire," he said.