Year	Kg per Square Metre
1980	24.62
1981	24.67
1982	24.71
1983	24.76
1984	24.81
1985	24.86
1986	24.89
1987	24.93
1988	24.97
1989	25
1990	25.02
1991	25
1992	24.93
1993	24.83
1994	24.73
1995	24.65
1996	24.61
1997	24.59
1998	24.6
1999	24.62
2000	24.66
2001	24.72
2002	24.8
2003	24.91
2004	25.02
2005	25.16
2006	25.28
2007	25.41
2008	25.55