Year	Kg per Square Metre
1980	23.3
1981	23.36
1982	23.42
1983	23.48
1984	23.53
1985	23.57
1986	23.61
1987	23.64
1988	23.69
1989	23.74
1990	23.8
1991	23.87
1992	23.94
1993	24.01
1994	24.07
1995	24.13
1996	24.21
1997	24.3
1998	24.4
1999	24.5
2000	24.58
2001	24.68
2002	24.77
2003	24.88
2004	25
2005	25.13
2006	25.24
2007	25.36
2008	25.5