October 14, 2016

expert reaction to international efforts to curb hydrofluorocarbon (HFC) gases

The US secretary of state John Kerry has said that there are international efforts to cut hydrofluorocarbon (HFC) greenhouse gases such as those used in air conditioners and refrigerators.

Prof. Keith Shine, Professor of Physical Meteorology at the University of Reading, said:

“One aspect that is important is that we should give a vote of thanks to the HFCs. Switching from these to CFCs helped mend the ozone layer, and stop the destruction getting worse, and although HFCs are greenhouse gases, they are less powerful than the CFCs they replaced, and this has actually helped reduce global warming. So, yes, it is good that they are being phased out, but to quote Dylan, ‘they helped us out of a jam I guess’.”

Dr Andrea Sella, Professor of Inorganic Chemistry at UCL, said:

“It is one of the ironies that HFCs are not harmful in the sense of being ‘toxic’ to people. It is their very safety and lack of flammability that makes them so suitable are refrigerants, just as CFCs and HCFCs have been in the past.

“The problem with them is two-fold. The first is that they are extremely robust molecules. Wrapping the central carbon atoms with fluorine makes them rather teflon-like. It gives the molecule a kind of chemical carapace that means that until they are hit by ultraviolet light nothing will really damage them – that means that they are not harmful to people beyond potentially acting as anaesthetics. It also means that they are destroyed very very slowly. But the presence of CF bonds means that these are extremely strong absorbers of infrared radiation, far far stronger than CO2. While CO2 is eventually scrubbed out of the atmosphere by dissolving into the oceans, HFCs will just linger in the atmosphere for thousands of years, continuing to absorb and contributing to the greenhouse effect. This is the reason for the huge concern about them.

“There are alternatives, however. Increasingly, refrigerators are being manufactured with hydrocarbon refrigerants (butane and pentane). While these are flammable the risk is sufficiently manageable as not to be a big problem. But there are also alternative refrigerants for air conditioning with global warming potentials (GWP) that are very close to zero. These are again fluorinated molecules, but ones that are constructed with a kind of Achilles heel that causes the molecule to break down when exposed to light and moisture. That said, they don’t just disappear and there is a concern that the breakdown products such as trifluoroacetic acid might eventually cause environmental concern.

“Another alternative is to use CO2 itself as the refrigerant and this is starting to be used ever more widely. However, CO2 requires much higher pressures than conventional refrigerants and that makes the engineering more complex and more expensive.

“But it’s worth mentioning that in some ways air conditioning is trying to put a sticking plaster onto a problem of a very different order. On the one hand we have rising temperature extremes that are the result primarily of CO2 emissions into the atmosphere. So addressing CO2 emissions is critical. But on top of that, putting in more air conditioning is likely to exacerbate the problems of extreme temperatures in cities due to the urban island effect, driving demand even higher. The need for air conditioning is also driven by poor building construction. I am not an expert in this area but the use of passive methods to control temperatures in buildings has to be a key strategy for the future to reduce the energy demand of buildings and cities generally. Better insulation, increasing thermal mass/inertia, reducing solar gain, improving ventilation/evaporative cooling, etc. will be needed to reduce the exponential rise of air conditioning in hot countries.”

Declared interests

None declared