Year	Kg per Square Metre
1980	26.41
1981	26.56
1982	26.71
1983	26.83
1984	26.98
1985	27.14
1986	27.29
1987	27.45
1988	27.61
1989	27.76
1990	27.9
1991	28.03
1992	28.15
1993	28.28
1994	28.42
1995	28.57
1996	28.73
1997	28.89
1998	29.03
1999	29.19
2000	29.36
2001	29.51
2002	29.66
2003	29.79
2004	29.94
2005	30.08
2006	30.21
2007	30.36
2008	30.51