In an op-ed for the Financial Times, Nouriel Roubini calls S&P's decision to downgrade the US credit rating "misguided," and he worries that it is making an already dangerous economic situation worse.  Between the US economy's inability to add jobs, and the economic stagnation and debt struggles in Europe, Roubini is expecting another global recession. And he fears that this one might be significantly worse than the last.

So can we avoid another severe recession? It might simply be mission impossible. The best bet is for those countries that have not lost market access - the US, UK, Japan, and Germany - to introduce new short-term fiscal stimulus while committing to medium-term fiscal austerity. The US downgrade will hasten demands for fiscal reduction, but America in particular should commit to look for significant cuts in the medium term, not an immediate fiscal drag that will worsen growth and deficits.

Most western central banks should also introduce further QE, even though its effect will be limited. The European Central Bank should not just stop rate hiking: it should cut rates to zero and make big purchases of government bonds to prevent Italy or Spain losing market access - the outcome of which would be a truly major crisis, requiring doubling (or tripling) of bail-out resources, or debt workouts and a eurozone break-up.

Read Mission impossible: stop another recession here.