It will never be established for sure whether what’s happened with China’s stock market gyrations would have had larger impact on the global economy than Grexit, although conjectures have certainly been offered suggesting that.
It’s useful to have some historical perspective on those fluctuations. A graphic on the Shanghai Stock Composite Index by Jan Zilinsky (PIIE, 10 July 2015) does this perfectly:
The blue line shows the Shanghai market experiencing a four-year (2009-2012) period of relative stability – thus showing calm is not impossible. The grey line indicates the four-year period (2005-2008), reflecting the more general worldwide bull market ending with the 2008 Global Financial Crisis: No exceptionalism and triumphalism warranted here, certainly.
And the most recent period (2013-) that is still incomplete in this 4-year window? That’s the red line. The decline has, of course, been sharp since the market peaked on 12 June 2015. Many people lost a lot of money. China’s government responded hastily and probably a bit too excitedly.
But this recent experience is a fluctuation that, in the cold light of recent historical experience, registers as far from dramatic.