Standard & Poor's has lowered Japan's credit rating outlook from "stable" to "negative," citing the economic effects of last month's combined earthquake, tsunami, and nuclear-reactor disasters. But markets took the news calmly. CNBC reports that 5-year and 10-year government bond yields were unchanged, and the Nikkei 225 index "actually gained 1.4 percent."

A trader at a U.S. brokerage, as quoted by Reuters, explained the situation thusly: "In February, Moody's warned on Japan's sovereign debt rating, so this is not news." Reuters adds that "market participants" considered a move like S&P's "inevitable considering Japan's fiscal situation."

This isn't to say that Japanese leaders can afford to be sanguine: Bloomberg notes that "today's decision adds to pressure on Prime Minister Naoto Kan, who has yet to detail how the rebuilding will be paid for and how he plans to rein in longer-term fiscal deficits." Still, Japan's reaction stands in marked contrast to that of the U.S., where a similar "negative" outlook from S&P earlier this month sent everybody into a panic.

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