Beef cattle contribute about 7% of national greenhouse gas emissions through the release of methane into the atmosphere. Cattle in northern Australia produce more methane per unit of beef produced because of tropical (C4) grasses and slower average growth rates. In this paper the level of emissions from different herds and some strategies to reduce emissions are modelled. The results indicate that few options exist to reduce methane emissions without reducing beef production. The opportunity costs of reducing methane emissions by reducing stocking rates are estimated at one Central Queensland location at $35 per ton of CO2 equivalent. Opportunity costs of destocking in northern Australia are estimated to lie between $50 and $75 per ton of CO2 equivalent.