From the evaporation of lakes and rivers to the extinction of rare species in its ravaged forests, the extent of environmental damage in Iran could, if left unchecked, pose a threat to the country arguably greater than that of any external adversary. Problems are particularly severe in urban areas, where vehicle emissions and industrial pollution are causing thousands of deaths from respiratory and heart disease each year. The capital Tehran, where 4.2m cars a day pump exhaust fumes into the haze above the city, bears most of the toll; in 2013, the health ministry said that more than 4,500 residents of the city of almost 9m had died as a result of air pollution that year.