Burning fossil fuels and clearing forests have lifted the carbon dioxide (CO2) levels in the atmosphere to 35% higher than before industrialisation, and other "greenhouse gases" such as methane and nitrous oxide from agriculture are also increasing.
Scientists worry that these gases will raise global temperatures, increase sea levels and lead to more extreme weather events, and have said the risk to future generations justifies cutting the growth in emissions.
• 80% of the increased concentration in these gases has come from 20% of the world's population in developed countries such as New Zealand.
• NZ contributes only 0.2% of the global emissions, but has the 12th-highest level of emissions on a per-head basis, at 18 tonnes of CO2 equivalent.
• The United Nations' Kyoto Protocol to reduce global emissions requires 38 developed countries take steps in the first period, 2008 to 2012.
• NZ's target is to stabilise its emissions at 1990 levels but they are running at 23% above the 1990 level - one of the highest increases in the developed world - mainly due to growth in transport and electricity emissions.
• The nation's "clean, green" brand and access to affluent markets is at risk if NZ fails to make its share of cuts.
• The Government says its emissions trading scheme (ETS) can help make those cuts by encouraging the planting of trees, building renewable energy source rather than thermal power stations, and investing in energy-efficient technology.
• The ETS requires emitters such as fuel and power companies to buy emissions units from businesses which have cut emissions or can store carbon like foresters, and the cost is passed on to consumers buying fuel or electricity.
• Forestry has been in the scheme since 2008.
• Transport, electricity and industry come into the scheme on July 1 but emitters only have to pay for half their emissions through to the end of 2012.
• The ETS will add 1c/kWh to the cost of electricity - about 5% - and 3.1c/litre to the cost of petrol, 3.3c/litre to diesel, adding up to $165 a year or $3.17 a week per household.
• Inflation-indexed superannuation and benefits take account of the impact of ETS on prices.
• Money from the ETS is going to foresters who have planted trees since 1990, and to businesses which have invested in renewable technology and energy efficiency to reduce emissions.
• The Government says that for the period to 2012, it will take $955 million from businesses but pay out $1.775 billion, mainly to foresters, leaving an $820 million shortfall for the taxpayer to pick up.
• The ETS is expected to reduce emissions by an estimated 19 million tonnes by 2012.
• But NZ is still expected to be short a gross 69 million units - equivalent to $2 billion at $30/tonne.
• It can buy other nations' credits offshore, or purchase credits from emission-reducing projects overseas, or offset credits from the 92 million tonnes of carbon expected to be stored in trees by 2012.
• The projected net surplus is 9.6 million tonnes, 2% inside NZ's target for the first commitment period.
• But many of the forests providing those credits will be felled, potentially incurring deforestation costs in the post-Kyoto period and leaving NZ back at 69 million tonnes (22%) over its target.
• Post-Kyoto, NZ has set policy targets of reducing emissions to 10% to 20% below 1990 levels by 2020, with a 50% reduction by 2050.
Sources: UK Department of Energy and Climate Change; www.climatechange.govt.nz; The Carbon Challenge (G. Bertram and S. Terry).
