Year	Kg per Square Metre
1980	19.86
1981	19.9
1982	19.94
1983	19.98
1984	20.03
1985	20.08
1986	20.13
1987	20.18
1988	20.23
1989	20.29
1990	20.35
1991	20.42
1992	20.5
1993	20.58
1994	20.67
1995	20.76
1996	20.86
1997	20.95
1998	21.01
1999	21.08
2000	21.15
2001	21.22
2002	21.3
2003	21.38
2004	21.46
2005	21.55
2006	21.65
2007	21.75
2008	21.86