In turn, this means that other sectors would need to reduce their pollution even further (at higher cost), or that Australia would need to rely more heavily on buying pollution reduction from overseas through international carbon markets. In addition, the Carbon Farming Initiative is estimated to drive emissions reductions in agriculture and forestry. Figure 3.2: Emissions reduction by sector with a carbon price Source: Treasury modelling, 2011 (core policy scenario). The coverage arrangements are summarised below and detailed in Appendix A, Table 4. Gases The carbon pricing mechanism will cover four of the six greenhouse gases counted under the Kyoto Protocol -- carbon dioxide, methane, nitrous oxide and per fluorocarbon emissions from the aluminium sector. The remaining greenhouse gases counted under the Kyoto Protocol (hydrofluorocarbons and sulphur hexafluoride) will face an equivalent carbon price, which will be applied through existing synthetic greenhouse gas legislation. Large polluters It is important to ensure that the carbon pricing mechanism is practical and minimises costs to business. For this reason, only firms that release over a certain amount of carbon pollution a year, or are large suppliers of natural gas, will pay the carbon price. Facilities that have direct greenhouse gas emissions of 25,000 tonnes of CO 2 -e a year or more (excluding emissions from transport fuels and some synthetic greenhouse gases) will be covered. There will be a lower threshold for certain landfill facilities. Retailers of natural gas will be liable for carbon pollution from the use of the fuels they supply