Year	metric tons
1981	5
1982	5
1983	5
1984	7
1985	7
1986	10
1987	9
1988	10
1989	4
1990	10
1991	9.86
1992	9.88
1993	9.91
1994	9.94
1995	10
1996	10.1
1997	10.23
1998	10.36
1999	10.62
2000	11
2001	12
2002	10
2003	10
2004	9.95
2005	9
2006	10
2007	10.96
2008	12.12
2009	13.12
2010	14.06
2011	14.97
2012	16
2013	16
2014	16.46
2015	17.92
2016	16.79
2017	16.75
2018	16.73
2019	17.57
2020	17.82
2021	17.37
2022	18.27