Global stock markets tumbled on Wednesday after ratings agency Fitch downgraded the United States' long-term credit rating — but top economists say there is nothing to worry about. U.S. stock futures were sharply lower after the downgrade, pointing to a fall of almost 300 points for the Dow Jones Industrial Average at the Wednesday open on Wall Street. Current Treasury Secretary Janet Yellen described the downgrade as "outdated." Phillips said the downgrade "should have little direct impact on financial markets as it is unlikely there are major holders of Treasury securities who would be forced to sell based on the ratings change." Harvey noted that, ahead of the 2011 S&P downgrade, stocks were in correction territory, credit spreads were widening, rates were falling, and the global financial crisis "was still in the market's collective conscience" — whereas the conditions today are "almost the opposite."

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Persons: Fitch, Larry Summers, Mohamed El, Erian, Summers, Janet Yellen, Goldman Sachs, Alec Phillips, Phillips, Wells, Chris Harvey, Harvey, Mark Mobius, they've, CNBC's Organizations: United, AAA, Dow Jones, U.S ., Allianz Chief, Treasury, Wells Fargo Securities Head, Equity, CNBC, ., Mobius Capital Partners Locations: United States, London, Asia, Pacific, Wells Fargo, U.S