Reports of the IPCC

The Intergovernmental Panel on Climate Change was established in 1988 by UNEP and WMO – World-Meteorological Organisation. It publishes reports on the status of the man-made climate changes in intervals, called Assessment Report, short AR4 or AR6, as base for political decisions. In this context the calculation methods for the impact and climate simulation models are developed. As the knowledge is developing, the calculation models and their results are adjusted. This leads a.o. to changes in values for GWP of refrigerants in every new report.

Sources: Deutsche IPCC-Koordinierungsstelle

IPCC Report 4

The GWP values of report AR4 of the year 2007 are base for the calculation of emission amounts and the limit values for application bans in the EU F-Gas Regulation 517/2014 and the Kigali Amendmend of 2016 of the Montreal Protocol.

Sources: Fourth IPCC-Status report – AR4

IPCC Report 6

The different parts of the report AR6 were published in 2021 and 2022. Important for refrigeration are some changes in values for GWP. As example, R32 goes from 675 in AR4 to 771 and thus above the often used limit value of 750. R152a moves from 124 to 164 and thus above the often used limit of 150, which also is seen in several application bans. Hydrocarbons, like propane and isobutane are now below 1, like many unsaturated partly fluorinated substances, e.g. R1234yf or R1234ze(E).

As the limit values were fixed with IPCC 4 values as a base, this report and its values will stay as base in many regulations.

Sources: Sixth IPCC report – AR6

Time horizon and values for GWP

The global warming potential GWP is a value accumulating the impact of a substance in the atmosphere over a given time. The value is calculated in direct comparison to the impact of carbon dioxide (CO₂). During the first years of discussions on the global warming, time horizons of 20 or 500 years were common. The short horizon allows better evaluation of the change impact of short time large scale emissions, while the longer horizon gives a better impression of the long term effects and additionally is closer to the atmospheric lifetime of important refrigerants used widely in the late 1980es, especially highly fluorinated compounds.

As the atmospheric life time of the reference fluid carbon dioxide at that time was estimated to approximately 120 .. 130 years and many partly fluorinated substances came to similar values, the time horizon of 100 years was established as standard value. The other values are also calculated and are included in the detail evaluations of the IPCC. At present, the atmospheric life time of carbon dioxide is stated as 5 .. 200 years. Unfortunately, the mechanisms for removal of the chosen reference fluid from the atmosphere are basically very different from the other substances to be evaluated in comparisons. With improvements in the understanding of the behaviour of refrigerants and especially of carbon dioxide in the atmosphere, the GWP values of the other substances will change.