Right now, 20% of the world’s  electricity goes into refrigeration, the technology behind air conditioning,  and keeping food and other goods cold.

What’s more, refrigeration  is responsible for about 8% of all global greenhouse gas emissions. And as the climate crisis continues,  we’re not going to need less cooling.

But we might be able to totally reinvent it. Here’s how. [♪ INTRO] There are two problems with refrigeration. One, the electricity that keeps us  cool in a warming world is of course causing emissions that make the problem worse.

But the chemicals that make the process work are themselves greenhouse gases, too. Problem is, we’ve been using the  same so-called vapor-compression cooling systems since the 19th century,  and it’s been a hard habit to break. Vapor compression works by using  a chemical called a refrigerant to pull heat out of where you don’t  want it, and dump it somewhere else.

When you get right down to it, heat  is just the movement of molecules. Something whose molecules are jiggling around is warmer than something where they’re more still. And the difference between phases  of matter, like liquid and gas, tends to involve a big jump in molecular motion.

Basically, you can absorb a bunch of heat by making something change  phase from liquid to gas. And if it takes that heat from the  air in your fridge (or your home) that air is going to get correspondingly colder. You could do this with water if you really wanted, but it needs to be 100 degrees  to change to gas phase.

So… fine, if you like your  apartment real tropical. Which brings us to vapor-compression refrigerants. When they’re pumped into  your fridge at low pressure, they will easily turn into  gas at a low temperature.

That means they’ll absorb some  of the heat from the fridge, even if it was cool to begin with. Outside the fridge, the gas is compressed  to pack its molecules tighter again, and it gives away heat as  it turns back into a liquid. Pump that liquid into the fridge, and  the refrigeration cycle can start again, keeping things cool as long  as the cycle continues.

In the 1930s, the refrigerants  known as Freons came into use. They were great at this  vapor-compression heat exchange. They had conveniently low boiling points, and were less unpleasant to use than  other known refrigerants, like ammonia.

However, decades later, it was  discovered that these chemicals were also great at stripping our  planet’s protective ozone layer. In 1987, almost all of the countries of  the world signed the Montreal Protocol, which laid out a path to phase out Freons. As a result, cooling systems  started switching over to a different class of chemicals:  hydrofluorocarbons, or HFCs.

They were also effective refrigerants,  and didn’t react with the ozone layer. But fast-forward a few more  decades, and it turned out that the ozone-friendly HFCs were still  causing trouble in the atmosphere. As a greenhouse gas, they can be up to almost two thousand times  more potent than CO2.

Oops. That discovery led to the Kigali Amendment, added to the Montreal Protocol in 2016. That Amendment says that by 2047, signatories will need to cut HFC use by over 80%.

Which creates a pretty strong  incentive to find new refrigerants. Annoyingly, though, the  alternatives proposed so far are pretty much all toxic,  inefficient, or flammable. But there’s another way.

We can ditch vapor compression altogether. Some modern green refrigeration technologies use something called the caloric effect. Many of these use solid refrigerants, which can’t leak and escape into the atmosphere.

When you apply an external force to  certain types of solid materials, that force causes their molecules  to move around in some fashion, and the material heats up. Remove that force, and the  molecules shuffle again, meaning the material cools down and is ready to absorb heat from the environment. It creates a totally different  kind of refrigeration cycle.

One example of this green cooling technology is called magnetocaloric refrigeration. It uses a magnetic field to  activate its solid refrigerant. And it does that pretty well.

The efficiency of any refrigeration  technology is measured against the so-called Carnot cycle,  which is a theoretical, ideal cycle of refrigeration with 100% efficiency. And in the lab, magnetocaloric  cooling reaches up to 60% efficiency. That’s better than most of the  good ol’ vapor-compression fridges.

But this technology needs  powerful magnetic fields, and it runs on rare-earth elements, like the expensive materials in your smartphone. So magnetocaloric cooling is a very costly option. Another green technology,  called elastocaloric cooling, is all about pushing and  pulling on a shape memory alloy.

Shape memory alloys do pretty  much what it says on the tin. You can mangle them as much  as you want when they're cold, and they'll return to their  previous shape when heated. A bit of rough handling modifies the  internal structure of shape memory alloys efficiently enough that the  molecular reshuffling releases heat.

Let go, and they’ll return to their original  structure, able to absorb heat once more. In the lab, elastocaloric cooling can  be as efficient as vapor compression, and it’s also more cost-effective than a  lot of other green refrigeration systems. But there's only so much brute  force a shape memory alloy can take, so researchers are looking  for ways to optimize them and make them resilient enough  for real-life refrigeration.

Then there’s ionocaloric  cooling, which works similarly to salting an icy road… and then un-salting it. See, when a salt dissolves  in water or other solvents, that lowers the freezing point of the solution. We’re talking chemical salts  here, so not just table salt, but any substance held together by ionic bonds.

Instead of freezing at zero  degrees, the salty water will stay liquid down to minus 10. And your drive to work is a little more slip-free. In ionocaloric cooling, a frozen  solvent is mixed with a salt.

The first version, published in 2022, used ethylene carbonate for the  solvent and sodium iodide for the salt. Just like ice on a road, this  concoction will now start to melt. Of course, that needs heat energy from somewhere.

But because it’s part solid, part  liquid, the heat from the liquid-y parts can help to break the bonds in the solid-y parts. But, and this is the clever part, breaking bonds absorbs heat without an increase in temperature. Effectively, that decreases the  overall amount of molecular motion and works out to the solvent cooling itself.

Afterwards, that salty slurry  is pumped away to ditch any heat it picked up from  the environment while melting. Once that’s done, electricity pulls  the salt ions out of the solvent; since ions are charged, this is easy to do. Without the salt, the solvent  will now easily freeze again, and give away the heat it needed to melt.

Ionocaloric refrigeration  is pretty energy-thrifty. You mostly need additional power to  pump the self-cooling slush around, and then filter the salt out. Unfortunately, so far, the actual  efficiency of ionocaloric cooling is only around 30%, plus the self-cooling  process itself takes a while, making it too slow for practical use right now.

But this technology is just a baby, so we’re likely to see a lot of improvement in the future. And even if your new fridge is not  going to run on salt anytime soon, we don’t have that much time to ditch vapor-compression cooling for something greener. So whether it’s magnets, elastics or ions, one of these days, your fridge  is going to have to stop vaping.

Thanks for watching this episode of SciShow, which was brought to you  with the help of our patrons. I really can’t stress enough that your  support makes these videos possible, and everyone can watch them,  so that’s darn nice of you. If you’d like to join our community, you  can get started at patreon.com/scishow. [♪ OUTRO]