New York University economist Nouriel Roubini earned the nickname "Dr. Doom" after he predicted much of the 2008 financial collapse.

He's hardly been optimistic since the financial crisis. He thinks 2013 will be trying for the global economy. Europe will be struggling with recession. China's economy is still soft, and he thinks U.S. economic growth will be modest at best.

But a perfect storm of four issues could make 2013 truly awful, Roubini said on an interview on Turkish television. Here they are:

The U.S. fiscal cliff issue doesn't get resolved. That means tax rates go up and government spending gets cut. The result, many economists believe, Roubini among them, will be another recession. We should note that President Obama and House and Senate leaders met Friday and swore they'd get the problem fixed. That was enough to turn a bad day for stocks into a winner.

The European recession gets nasty. This would occur if Greece runs out of cash (a real possibility) and leaves the euro currency in a messy way. Read that as this: Greece basically defaults on its debt and plunges global credit markets into chaos.

China's economy tanks. It's possible. Real estate in many Chinese markets has been overbuilt, and construction spending has slowed. The Shanghai Composite Index, the benchmark Chinese stock index, is down 34% since April 2011 and 67% since peaking in November 2007. Hong Kong's Hang Seng Index, however, suggests things aren't that bad. The index is up 15% this year.

War erupts in the Middle East. This assumes Israel and Iran somehow go to war, not a huge possibility by itself. But the rising tensions between Israel and Syria and Israel and Egypt over what Israeli forces might do in the Gaza Strip could cause major disruptions in crude oil markets, with crude oil pushing toward $200 a barrel with serious effects on the global economy.

So far, however, oil markets aren't in a panic mode.

Crude oil (-CL) for January delivery in New York settled up $1.05 to $86.92 a barrel Friday and was up 1% on the week. Brent crude, the better indicator to watch in this case, was up 97 cents to $108.98 a barrel and is down slightly for the week.

Wholesale gasoline futures for December delivery ended the day up 1.39 cents to $2.7101 a gallon.

AAA's national average retail price of gasoline was $3.43 a gallon Friday, down slightly from Thursday and down 9.4% this quarter.

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