Year	million ton-km
1970	0.400000006
1971	0.400000006
1972	0.5
1973	0.5
1974	0.6000000238
1975	2
1976	1.3999999762
1977	1.5
1978	1.6000000238
1979	1.7999999523
1980	2.5
1981	2.9000000954
1982	2.7000000477
1983	3.9000000954
1984	4.5999999046
1985	6.6999998093
1986	6.1999998093
1987	5.9000000954
1988	27.8999996185
1989	10.5
1990	11.1999998093
1991	23.8999996185
1992	13.8000001907
1993	18.2999992371
1994	16
1995	16.8999996185
1996	17.8999996185
1997	17.8999996185
1998	15.6000003815
1999	16
2000	16.997
2001	16.178
2002	5.477
2003	5.751
2004	6.73
2005	6.936
2006	7.212
2007	7.643000000000001
2008	7.233
2009	6.282
2010	6.463516539
2011	6.48656488020303
2012	5.76237493105865
2013	5.759868
2014	4.5996
2015	4.536371616
2016	4.895080058
2017	4.5668399023
2018	8.84572
2019	5.847551
2020	13.689186
2021	17.307683