Year	constant 2015 US$
1973	390000
1974	32040000
1975	33880000
1976	27530000
1977	13740000
1978	10510000
1979	5440000
1980	18880000
1981	26320000
1982	18980000
1983	15900000
1984	13160000
1985	16480000
1986	22910000
1987	18790000
1988	27970000
1989	28030000
1990	17110000
1991	31120000
1992	34390000
1993	32740000
1994	41290000
1995	56760000
1996	44370000
1997	31750000
1998	8240000
1999	30350000
2000	11940000
2001	24550000
2002	43290000
2003	17810000
2004	-19410000
2005	11180000
2006	19390000
2007	18260000
2008	14290000
2009	35090000
2010	37290000
2011	29920000
2012	23870000
2013	22320000
2014	17300000
2015	14080000
2016	15230000
2017	12500000