This autumn the dials on Goldman Sachs' forecasting machine are spinning in a startling manner. Last month, the US bank's leading composite indicator of economic growth surged at a record rate – suggesting that western economies will rebound sharply in the second half of this year.

More startling, Goldman's so-called “financial stress index”, which measures different elements of market health, has recently risen to levels not seen since before the near-failure of Bear Stearns in the spring of 2008.

“Looking at virtually everything we think is relevant as leading indicators, it looks good for the G20 area and asset markets,” Jim O' Neill, chief economist, told Goldman clients earlier this week in an e-mail, which likened this dramatic trajectory to a “Usain Bolt celebration”.