Key-features:

• Carbon dioxide (CO₂) is the most important greenhouse gas now and will increase in importance over this century, both absolutely and relative to the other greenhouse gases. As a consequence, energy efficiency remains of paramount importance.
  
• Greenhouse gases whose emissions are controlled under the Kyoto Protocol comprise carbon dioxide, methane, nitrous oxide and the fluorinated gases - HFCs, PFCs and SF₆.
  
• The relative position of HFCs, PFCs and SF₆ has remained about the same. Even after taking into account their high Global Warming Potentials (GWPs) (2).
  
• They are currently very minor contributors to climate change (their total effect is a small fraction of a percent) and
  
• Their combined contributions are predicted to reach only two or three percent of the total "radiative forcing" from all greenhouse gases by the end of this century.
  
• By far the largest "halocarbon" contribution comes from the CFCs present in the atmosphere. The concentrations of these will decline as a consequence of the Montreal Protocol.
  
• The GWPs of greenhouse gases have not changed markedly between the SAR and the TAR. For example, the value assigned to HFC-134a, the fluorocarbon refrigerant most widely used, has remained at 1300. For the most abundant PFC, carbon tetrafluoride emitted principally from aluminium smelting, the value has fallen from 6500 to 5700 and for SF₆, the reduction is from 23900 to 22200.
  
• None of these changes is significant; uncertainty in GWP is stated to be ±35% (for both the SAR and TAR values), which covers the range of changes more than adequately. The TAR carries a more complete listing on pages 388-391.
  
• A table of GWPs of some of the more common greenhouse gases is attached. For the purposes of the Kyoto Protocol, the GWPs given in the Second Assessment Report must be used.

(April 2003)