Year	U.S. dollars (Units)
1980	479.601
1981	501.744
1982	552.581
1983	469.374
1984	539.979
1985	450.535
1986	330.043
1987	281.362
1988	451.564
1989	405.247
1990	219.455
1991	261.748
1992	228.231
1993	259.186
1994	308.752
1995	295.710
1996	318.646
1997	286.074
1998	223.939
1999	218.906
2000	205.251
2001	228.033
2002	251.704
2003	265.323
2004	264.775
2005	285.106
2006	323.259
2007	360.425
2008	409.443
2009	391.213
2010	401.835
2011	448.324
2012	566.370
2013	716.148
2014	713.530
2015	592.903
2016	525.948
2017	495.812
2018	533.972
2019	521.396
2020	508.812
2021	509.482
2022	492.796
2023	460.598
2024	526.587
2025	520.125
2026	520.184
2027	533.541
2028	552.159
2029	572.058