Year	Kg per Square Metre
1980	20.33
1981	20.4
1982	20.44
1983	20.48
1984	20.52
1985	20.58
1986	20.63
1987	20.67
1988	20.75
1989	20.84
1990	20.93
1991	21.02
1992	21.1
1993	21.15
1994	21.25
1995	21.35
1996	21.45
1997	21.55
1998	21.66
1999	21.76
2000	21.86
2001	21.97
2002	22.07
2003	22.19
2004	22.3
2005	22.4
2006	22.52
2007	22.63
2008	22.74