The world economy could have its worst year since the Great Depression, the World Bank has warned. Even if the European crisis gets no worse, the world is headed for another year of weak growth, says the prestigious bank. And if Europe goes down, it takes the world with it: the Bank expects a shock as bad or worse as the 2008-2009 downturn.Last summer the World Bank was forecasting global growth at 3.6 percent in 2012; the latest forecast scales that back to 2.5 percent — slower than in 2011. The Bank now expects a recession in Europe, tepid growth in the US, and sharply slowed growth in the developing world and emerging markets.And that is assuming Europe doesn’t melt down. If Europe goes, we are back to the darkest days of 2008-09, and things could be worse this time around.The Bank’s forecasters, like all economic forecasters, are often wrong. Let’s hope this is another case. The US economy in particular has been showing real signs of recovery and 2012 could still turn out better than expected. But thoughtful investors will be watching global data with apprehensive eyes; the World Bank warning is not what they wanted to hear.