Year	Kg per Square Metre
1980	22.57
1981	22.63
1982	22.7
1983	22.76
1984	22.83
1985	22.88
1986	22.94
1987	23
1988	23.06
1989	23.13
1990	23.2
1991	23.27
1992	23.33
1993	23.4
1994	23.47
1995	23.54
1996	23.6
1997	23.66
1998	23.7
1999	23.73
2000	23.76
2001	23.78
2002	23.78
2003	23.79
2004	23.8
2005	23.81
2006	23.82
2007	23.83
2008	23.84