Year	Kg per Square Metre
1980	18.68
1981	18.71
1982	18.74
1983	18.77
1984	18.81
1985	18.87
1986	18.93
1987	18.99
1988	19.06
1989	19.14
1990	19.22
1991	19.29
1992	19.36
1993	19.43
1994	19.5
1995	19.58
1996	19.65
1997	19.73
1998	19.81
1999	19.9
2000	19.98
2001	20.08
2002	20.16
2003	20.25
2004	20.35
2005	20.44
2006	20.54
2007	20.63
2008	20.73