Shares in Carnival steamed ahead after the cruise operator posted strong earnings for the fourth quarter and issued a bullish update for 2011.The company, which operates P&O and other brands, was helped by a gradually recovering economy. Fourth quarter earnings rose to $31 a share from $0.24 in the same period the previous year. Revenues rose to $3.5bn from $3.3bn.Carnival posted full-year earnings of $2.47 a share, up from $2.24 the previous year. It expects to earn between $2.90 and $3.10 next year."Since last September, booking volumes continued to be strong and prices for those bookings are higher than last year," the company said.