Many chemical compounds found in the Earth’s atmosphere act as greenhouse gases (GHG). These gases allow sunlight to enter the atmosphere freely. When sunlight strikes the Earth’s surface, some of it is reflected back towards space as infrared radiation (heat). GHG absorb this infrared radiation and trap the heat in the atmosphere, in other words they act like a greenhouse. Over time, the amount of energy sent from the sun to the Earth’s surface should be about the same as the amount of energy radiated back into space, leaving the temperature of the Earth’s surface roughly constant. Many gases exhibit these "greenhouse" properties.
The most significant greenhouse gases are:
carbon dioxide (CO2)
nitrous oxide (N2O)
sulphur hexafluoride (SF6).
The New Zealand Situation:
In December 2002 New Zealand ratified the Kyoto Protocol. If it enters into force, this will legally bind New Zealand to reduce greenhouse gas emissions over the Protocol’s first commitment period, 2008–12, to 1990 levels. New Zealand will be required to take responsibility for any excess emissions if this is not achieved. Recent analysis of New Zealand’s GHG emissions shows that CO2 has overtaken CH4 as our most significant GHG, making up 45% of total emissions in 2001, with CH4 contributing 38%. Nitrous oxide contributes about 17%, and emissions of HFCs, PFCs, and SF6 make up less than 1% of the national total.
A very good summary of GHG can be found at this US Government site.
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