The other greenhouse gases you don’t think about
During the United Nations climate change meeting in Durban last year, there was lots of talk about carbon dioxide, which has a bad rap for trapping heat in the atmosphere and so leading to global warming.
But what about the other greenhouse gases? How much do they contribute to climate change? Here’s a handy guide.
What’s global warming potential? It’s a measure of how much heat a gas traps in the atmosphere,
and depends on a number of things:
– It’s compared to carbon dioxide. For convenience, we assign one ton of carbon dioxide the
abstract value of 1.
– How long does the gas linger in the atmosphere? The longer it sticks around, the longer it can
do its thing.
– What wavelength(s) of radiation does it absorb?
Global warming potential (GWP for short) is typically calculated over a 20, 50 or 100-year
timeframe. For example, methane hangs around in the atmosphere for 12 years. (See page 212 of this IPCC 4th Assessment Report chapter for a chart of how much and how long.)
These are the ‘other’ greenhouse gases that the Kyoto Protocol recognises:
Methane (CH4): which comes from natural sources such as wetlands, and man-made sources such as cows (they’re anthropogenic thanks to our demand for beef), landfills and fossil fuel extraction.
Nitrous oxide (N2O): comes from natural and anthropogenic sources, but particularly fertiliser use and industrial processes
Hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs): industrial gases used as refrigerants, solvents, surfactants, etc.
Sulphur hexafluoride (SF6): This potent greenhouse gas is used as an electrical insulator in power distribution equipment
The potential ‘new’ greenhouse gas: Nitrogen trifluoride (NF3)
In new drafts of Kyoto Protocol documents last year, nitrogen trifluoride was added to the list of controlled greenhouse gases. It’s used in the microelectronics industry (that means you, Singapore!) to etch computer chips, and in the making of flat LCD screens.
It sticks around in the atmosphere for 550 years, and by some accounts is 17,000 times more effective a greenhouse gas per ton than carbon dioxide over a century.
The bad news is, as the demand for high-tech products continues to grow, the industrial use of NF3 will also continue to expand. The good news? Elemental fluorine has potential to be an alternative, and proper gas abatement processes may be able to control industrial NF3 emissions.
The IPCC 4th Assessment Report (5AR due out in a few years!)