The persistent European debt crisis, the messy U.S. fiscal situation, and the slowing Chinese economy all continue to pose threats to the global economy in 2012.

Lately, sentiment has turned more positive driven in large part by the ECB's long term refinancing operation (LTRO). Also, U.S. data has improved on driven by a dip in household savings, monetary easing, and an unseasonably warm winter.

But the current optimism is "only a temporary bright spell," write SocGen's economists in a new research note. They argue that the problems of plaguing the global economy can't be fixed through balance sheet expansion.