The GWP (Global Warming Potential) is an index, specific to each gas, which expresses its climatic warming potential relative to that of carbon dioxide, which by convention is set at 1. It enables to compare the impacts of emissions and reductions of different greenhouse gases. According to the IPCC, GWPs typically have an uncertainty of ±35 percent.
The GWP is actually calculated in terms of the 100 year warming potential of a kilogram (kg) of a gas relative to that of a kilogram of CO2.
Because the decay of CO2 in the atmosphere follows a different pathway than the other Greenhouse Gases (see figure), the time horizon plays a role in the GWP values. The parties to the UNFCCC have also agreed to use GWPs based upon a 100 year time horizon.
On its own however, GWP cannot describe the climate impact of a Greenhouse Gas, as explained in the next section.
The longer a greenhouse gas stays in the atmosphere, the more its cumulative heating effect. Although the GWPS are calculated on a 100 years basis, lifetime becomes an important parameter for the longer term.
Actually, CO2 has a very long lifetime: it remains in the atmosphere for several thousand years and after 100 years has developed less than one quarter of its impact.
In contrast, HFCs are quickly removed from the atmosphere due to their relatively short atmospheric lifetimes, and their lifetimes are decades or less.
The long lifetime of CO2 means a significant commitment for climate change long into the future. Compared to CO2, HFCs are quickly removed from the atmosphere due to their relatively short atmospheric lifetimes.
The GWP has to be put into perspective. The total quantity released is as important as the GWP in calculating the real environmental impact.
IMPACT= INDEX x QUANTITY
Clearly GWP as a measure does not satisfactorily describe the climate impact of a greenhouse gas.
Despite the low GWP of CO2, the enormous quantities emitted and its long lifetime means that it has a far greater impact on climate than HFCs. Currently, CO2 emissions contribute 64% of the total greenhouse gas emissions and are rising.
In contrast the Summary for Policymakers (SROC) has concluded that the HFC radiative forcing (cumulative contribution to global warming) will remain below 1% of the estimated radiative forcing of all greenhouse gases in 2015, and, in terms of yearly emissions, they will account for 2 % of greenhouse gas emissions.
The atmosphere naturally contains greenhouse gases such as CO2,methane and water vapour that have maintained a mean terrestrial temperature around 15°C. Humans are adding carbon dioxide into the atmosphere by burning fossil fuels for power, transportation and industry. Agriculture also leads to methane emissions.
These sharp increases in greenhouse gases change the climate balance. When considering impacts, the relative quantities of greenhouse gases emitted to the atmosphere must be taken into account; HFCs are emitted in tiny quantities compared to CO2 or methane (table 2).
A recent publication ‘Releases of refrigerant gases to the atmosphere’ (Atmosph.Envir, 2003) concluded that significantly less HFC are used to replace the same amount of CFCs for refrigeration and air conditioning.
In reaching its conclusions, the report raised three important points :
So far only about 30 per cent of uses have been so substituted but the cooling carried out by CFCs, and to an extent HCFCs, is now being replaced by a whole range of technologies, including HFCs, ammonia and hydrocarbons. This is why the resulting emissions from the use of HFCs were about 0.5 per cent of total global GHG emissions in 2002 and the global contribution of all HFC emissions is likely to remain at or below a maximum of 2 per cent by the middle of the century.
Thanks to the Fluorocarbons (and SF6) energy efficiency, considerable energy savings can be obtained :
Verified LCA (Life Cycle Analysis) have been released and published and can be downloaded from this site or requested in written.
For building insulation, their excellent thermal effectiveness as blowing agents is an asset for reducing the energy demand for heating and for cooling. (for ex in warm climates).
Industry response to the CFC issue by A. McCulloch - University of Bristol
Symposium, 7 May 2010 honouring Joe Farman and celebrating 25 years ince publication of the Ozone Hole Paper in Nature – High and Low lights.