Good explanations please

Q13. [E] Low real rates. As the graph below (reproduced from the Wall Street Journal?) shows, real interest rates have been trending downwards for some decades now. How would you explain this? Down Down Down Lower real natural interest rates have held down the federal-funds rate, leading some economists to call for letting inflation drift higher. 20% 15 10 Fed's target* 5 Annual inflation 0 Federal- funds rate Real natural -5 rate 1975 80 |2000 10 * The Fed formally adopted a 2%% inflation target in 2012. Note: Inflation is measured using the personal-consumption expenditures price index. Real natural rate is measured using the Laubach and Williams framework Sources: Commerce Department (inflation); Federal Reserve (federal-funds rate); Thomas Laubach and John Williams, Federal Reserve Bank of San Francisco (real natural interest rate) THE WALL STREET JOURNAL