So surprisingly, the best hope for clean, green ethanol right now is to ship it in diesel-powered trucks.

FORBES: Ethanol: Getting There Is None Of The Fun

"During regularly scheduled testing of the ship's emergency diesel generator, a malfunction occurred, " Carnival said in a statement.

CNN: STORY HIGHLIGHTS

Carnival said the ship's emergency diesel generator failed, but the cruise line disputed notions of a widespread system failure.

CNN: STORY HIGHLIGHTS

In a statement, Carnival said the ship's emergency diesel generator failed.

CNN: STORY HIGHLIGHTS

Last month, the MS Nordkapp cruise ship hit rocks near Deception Island, off the Antarctic Peninsula, spilling diesel oil into the bay.

CNN: Antarctica: March of the tourists