Thomas Oatley and Kindred Winecoff try to calm us down:
Further economic and financial deterioration in Greece would certainly have negative impacts there and might adversely affect Greece's southern European neighbors, who are facing similar circumstances. But financial weakness in Greece is unlikely to spark a global crisis analogous to the one triggered by Lehman Brothers' collapse in September 2008 — even if economic woes eventually force Greece to exit the monetary union.
Instead, the global consequences of southern Europe's debt crisis are more likely to resemble the Latin American sovereign debt crises of the early 1980s, the East Asian crises of 1997-1998, and Argentina's crisis at the turn of the millennium. Each of these had significant local effects — widespread bank failures, sharp increases in unemployment, large exchange-rate devaluations, deep recessions — that were not transmitted globally.