The message from this week’s sell off in global stock markets could not be clearer: The summer time rally, fueled by optimism over central bank stimulus measures, is now over and it’s time to brace for a period of renewed volatility and uncertainty, analysts say.

The S&P 500 index on Tuesday suffered its worst day in three months, while Asian stocks slumped on Wednesday, with Japan’s benchmark Nikkei stock index down 1.7 percent in early trade. The sharp sell-off and renewed concerns about Spain’s economy are likely to set the tone for European markets on Wednesday.