How supermarket freezers are heating the planet, and how they could change

Climate-conscious shoppers may buy local food and try to cut packaging waste, but those efforts could be negated by potent greenhouse gases leaking from supermarket fridges.

Refrigerants called hydrofluorocarbons or HFCs are widely used to keep food cold or frozen at grocery stores and during transport. (They're also used for other refrigeration applications, like ice rinks and air conditioners).

They were originally brought in to replace ozone-depleting refrigerants called chlorofluorocarbons (CFCs), which were banned in a landmark 1987 agreement called the Montreal Protocol, in order to save the Earth's protective ozone layer.

But HFCs are themselves powerful greenhouse gases.

Typically, each tonne of HFCs can trap as much heat in the atmosphere as 1,400 to 4,000 tonnes of carbon dioxide over 100 years, depending on the type of HFC.

Here's a look at why that's happening, what the solutions are, and how ordinary shoppers could make a difference.

Supermarket fridges aren't like your fridge at home, which contains only about five kilograms of refrigerant in a sealed unit that's unlikely to leak, says Morgan Smith, spokesperson for the North American Sustainable Refrigeration Council.

Her non-profit group has partnered with industry to help enable the transition from HFCs to more climate-friendly refrigerants because the complexity of their systems make them prone to leaking significant amounts of HFCs. 

Beneath and behind the cases of vegetables, dairy and frozen foods at a typical supermarket are kilometres of piping with thousands of valves, containing literally a tonne of refrigerant. 

"It's so large and so complex, with so many different points of connection that those systems are inherently leaky, and so they leak about 25 per cent of their refrigerant charge every year," said Smith.

That's something another non-profit group called the Environmental Investigation Agency has captured on video using infrared cameras and HFC detectors in U.S. grocery stores. It also measured levels of HFCs in the store using chemical detectors.

It detected leaks at 55 per cent of the dozens of U.S. stores where it took measurements. On average, it found a single supermarket emits 875 pounds (400 kilograms) of HFCs a year, equivalent to carbon emissions from 300 cars. In the U.S. alone, it calculated supermarket HFC leaks cause as much global warming as burning 22 million tonnes of coal. 

HFCs are such a big problem for climate change that Canada and 196 other countries have signed an international agreement, the Kigali Amendment to the Montreal Protocol, to reduce HFC consumption 85 per cent by 2036, relative to 2011 to 2013.

Sheli Miller, a professor who studies the environmental impact of the food system at the University of Michigan, says emissions from refrigerants may be relatively small compared to the food system emissions overall and major categories such as food waste.