As a result, productivity gains will be instrumental in driving GDP growth. To sustain the recent growth trajectory, productivity will need to accelerate to nearly twice its historical rate. Simply maintaining the fifty-year historical rate of productivity growth over the coming fifty years will cut the global economic growth rate from 3.6 percent annually to 2.1 percent annually. Rather than expand sixfold, as it did in the past fifty years, the global economy would only expand threefold in the coming fifty years.