This may be the way the world ends — not with a bang but with a temper tantrum.

O.K., a temporary government shutdown — which became almost inevitable after Sunday’s House vote to provide government funding only on unacceptable conditions — wouldn’t be the end of the world. But a U.S. government default, which will happen unless Congress raises the debt ceiling soon, might cause financial catastrophe. Unfortunately, many Republicans either don’t understand this or don’t care.

Let’s talk first about the economics.

After the government shutdowns of 1995 and 1996 many observers concluded that such events, while clearly bad, aren’t catastrophes: essential services continue, and the result is a major nuisance but no lasting harm. That’s still partly true, but it’s important to note that the Clinton-era shutdowns took place against the background of a booming economy. Today we have a weak economy, with falling government spending one main cause of that weakness. A shutdown would amount to a further economic hit, which could become a big deal if the shutdown went on for a long time.

Still, a government shutdown looks benign compared with the possibility that Congress might refuse to raise the debt ceiling.

First of all, hitting the ceiling would force a huge, immediate spending cut, almost surely pushing America back into recession. Beyond that, failure to raise the ceiling would mean missed payments on existing U.S. government debt. And that might have terrifying consequences.