Year	Kg per Square Metre
1980	28.07
1981	28.13
1982	28.18
1983	28.24
1984	28.32
1985	28.38
1986	28.45
1987	28.52
1988	28.6
1989	28.7
1990	28.69
1991	28.73
1992	28.85
1993	29.03
1994	29.2
1995	29.38
1996	29.56
1997	29.71
1998	29.86
1999	30
2000	30.14
2001	30.26
2002	30.34
2003	30.45
2004	30.57
2005	30.72
2006	30.87
2007	31.01
2008	31.16