The arguments for cutting subsidies are not new. But the I.M.F.’s exhaustive research makes the case even stronger and more timely. The fund calculates that by raising taxes on fossil fuels, basically eliminating the subsidies, nations would reduce premature deaths caused by air pollution by 55 percent. That would make a big dent in the 3.7 million premature deaths that the World Health Organization links to all outdoor air pollution for just 2012.