 However, air pollution remains a severe problem, especially in the industrialised north, reaching the tenth highest level worldwide of industrial carbon dioxide emissions in the 1990s.Italy is the twelfth largest carbon dioxide producer.Extensive traffic and congestion in the largest metropolitan areas continue to cause severe environmental and health issues, even if smog levels have decreased dramatically since the 1970s and 1980s, and the presence of smog is becoming an increasingly rarer phenomenon and levels of sulphur dioxide are decreasing.