Production of tobacco leaf increased by 40% between 1971, when 4.2 million tons of leaf were produced, and 1997, when 5.9 million tons of leaf were produced. According to the Food and Agriculture organization of the UN, tobacco leaf production was expected to hit 7.1 million tons by 2010. This number is a bit lower than the record-high production of 1992, when 7.5 million tons of leaf were produced. The production growth was almost entirely due to increased productivity by developing nations, where production increased by 128%. During that same time, production in developed countries actually decreased. Chinas increase in tobacco production was the single biggest factor in the increase in world production. Chinas share of the world market increased from 17% in 1971 to 47% in 1997. This growth can be partially explained by the existence of a high import tariff on foreign tobacco entering China. While this tariff has been reduced from 64% in 1999 to 10% in 2004, it still has led to local, Chinese cigarettes being preferred over foreign cigarettes because of their lower cost.
Question: How many more million tons of tobacco leaf were produced in 1997 compared to 1971?
Answer: 1.7