Governments of emerging market economies will fail in their attempts to stem the appreciation of their currencies, Brown Brothers Harriman has forecast.Speaking to Bloomberg in New York, Win Thin, a senior currency strategist at the investment house, said countries such as South Korea and Brazil may be able to stem the rise in their respective currencies, but will be unable to halt or reverse it.Brazil's real has been the best-performing currency in 2009, with a 34 per cent rise witnessed since the beginning of the year. Earlier this week, the government declared it would impose a tax to iron out a "distortion" that had developed since the introduction of a levy on foreign purchases of bonds and stocks last month.Other emerging-market nations such as India, South Korea, Indonesia and Kazakhstan have also expressed an intention to introduce such measures."The strengthening of the currencies we're seeing in many emerging markets is caused by very solid growth expectations, improvement of credit fundamentals and stock exchange gains. I don't think they can totally stop the appreciation," commented an analyst at RBC in Toronto.