NOTES: World greenhouse gas emissions from human activities, mainly burning fossil fuels, totalled about 40 billion tonnes in 2000. The table assumes that prices for emitting carbon dioxide, the main greenhouse gas, stay below US$100 a tonne.

CURBS FROM EXISTING TECHNOLOGIES

-- ENERGY SUPPLY: more efficient supply and distribution, combined heat and power, switching from high-polluting coal to cleaner gas, nuclear power and renewable energies such as hydropower, solar, wind, geothermal and bio energy. Can also include some early applications of carbon capture and storage.

-- TRANSPORT: more fuel-efficient vehicles, hybrids, cleaner diesel, better public transport, bicycles.

-- BUILDINGS: efficient lighting, more effective insulation and ventilation, passive solar design for heating, cooling and ventilation, more efficient electrical appliances and heating and cooling devices, alternative refrigerants, better recycling.

-- INDUSTRY: Efficient electrical equipment, heat and power reuse, material recycling, control of non carbon dioxide gases.

-- AGRICULTURE: Improved management of crop and grazing land to improve soil carbon storage, restoration of degraded lands, better rice cultivation. Improved management of livestock and manure to reduce methane emissions. Better use of fertilisers, bio-energy crops to replace fossil fuels.

-- FORESTRY: Planting more trees, slowing rates of deforestation and land degradation, use of wood for bio-energy to replace fossil fuels.

-- WASTE: Tapping methane from landfills, incineration of waste with use of the energy, composting of organic waste, recycling and minimising waste.

CURBS FROM FUTURE TECHNOLOGIES

-- ENERGY SUPPLY: Carbon capture and storage for gas, biomass or coal-fired power plants, advanced nuclear power and renewable energies.

-- TRANSPORT: Hydrogen-powered fuel cell vehicles, second generation biofuels, more efficient aircraft, advanced electric and hybrid vehicles with better batteries.

-- BUILDINGS: Integrated solar photovoltaic electricity supplies, smart metering and intelligent control.

-- INDUSTRY: Advanced energy efficiency, carbon capture and storage for cement, ammonia, fertiliser and steel production, inert electrodes for aluminium manufacture.

-- AGRICULTURE: Genetic technologies to improve energy crops