Year	million ton-km
1970	0.1000000015
1971	0.1000000015
1972	0.200000003
1973	0.200000003
1974	0.200000003
1975	0.200000003
1976	0.200000003
1977	0.3000000119
1978	0.3000000119
1979	0.400000006
1980	0.5
1981	3.4000000954
1982	4.0999999046
1983	3.9000000954
1984	3.9000000954
1985	3.2999999523
1986	3.5
1987	3.9000000954
1988	4.4000000954
1989	7.9000000954
1990	8.6999998093
1991	5
2010	0
2011	1.52106019
2012	1.275841047
2013	1.440588
2014	1.363692
2018	0
2019	0