Year	Kg per Square Metre
1980	21.71
1981	21.89
1982	22.05
1983	22.26
1984	22.51
1985	22.76
1986	22.97
1987	23.16
1988	23.36
1989	23.51
1990	23.61
1991	23.71
1992	23.86
1993	24.05
1994	24.25
1995	24.4
1996	24.56
1997	24.71
1998	24.88
1999	25.07
2000	25.24
2001	25.4
2002	25.56
2003	25.7
2004	25.82
2005	25.95
2006	26.1
2007	26.26
2008	26.41