Okay, when the weather outside is frightful,   what’s a person gotta do to  get some delight up in here?

Well, that depends on where and when you live. We humans have harnessed imaginative ways   of heating and cooling our  homes throughout the ages.

For centuries, Korean houses stayed toasty  with built-in floor warmers. In ancient Persia,   cooling towers called wind-catchers made  the desert a bearable place to live. And today, here at Crash Course  Headquarters, comfort is as simple   as turning up the dial on a thermostat.

But that convenience comes at a price.   Heating and cooling homes and commercial buildings leads to  about 7% of all global carbon dioxide emissions   every year — which doesn’t sound like  that much until you realize that that   translates to more than 3.5 billion tons. And those surges of carbon dioxide   are cranking up the thermostat on our  planet at unprecedented rates. As temperatures soar outdoors, one  of our biggest challenges will be   rethinking how we manage temperatures  indoors—and making reliable, carbon-free   heating and cooling available to everyone.

Hi hi! I'm M Jackson and this is Crash Course Climate and Energy. [INTRO] When I pump up the heat in our studio,  I’m tapping into a resource hundreds of   millions of years in the making: natural gas. As a fossil fuel, it’s derived from decomposed   plants and creatures that lived before the  dinosaurs, like these cuties.

I like to imagine   I owe my piping-hot bubble bath to them. But natural gas consists mostly of methane,   one of the notorious greenhouse gases.  And our means of extracting methane   contributes to climate change, contaminates  water, and can even cause earthquakes. I’m talking about fracking.

No, not the PG-version of a cuss, hollered   when you stub your toe in front of your parents. Fracking is a way of extracting natural gas or   crude oil from deep below Earth’s surface.  It uses high-pressure drilling and fluid to   fracture underground rocks — hence the  “frack” — and releases the gas within. But it also has some big side-effects.

Notably, in 2003, a new fracking method   burst onto the scene, just as the U. S.  natural gas supply was declining. By using mostly water instead of expensive gels,  and drilling not just down but also horizontally,   this new method made it possible to  extract more natural gas than ever before,   and more cheaply, from rock called shale.

The fracking boom boosted the U. S. economy.   Extracting gas within U. S. borders instead of  importing it helped create 2.8 million jobs   and generate trillions of dollars in revenue.

Sounds like a net positive, right! Ah, if only. The downside is that extracting natural  gas from shale is messy.

Some methane   inevitably escapes into the atmosphere. It’d be like if whenever you sipped soda   from a straw, some of it came out the side  of your mouth. Except here that soda is methane.

This greenhouse gas traps 80 times  as much heat as carbon dioxide in its   first 20 years of entering the atmosphere. Global methane levels have spiked since 2007.   The fracking boom, which has since spread beyond  the U. S., is a prime suspect in that who-dun-it.

Another problem? Used-up fracking wells  keep releasing methane even if they don’t   get plugged up, which costs millions of  dollars, and doesn’t always happen. To make matters even worse, pipelines transporting  oil and natural gas from fracking sites leak,   which can threaten nearby communities.

For instance, the Standing Rock Sioux Tribe   protested the construction of the Dakota  Access pipeline which was built in 2017,   and today runs directly beneath one of  the Reservation’s main water sources. So, overall, natural gas is a major —  and majorly complicated — energy source.   But it will also likely play a big part  in decarbonizing energy worldwide. Burning natural gas actually  releases significantly less   carbon than burning other fossil  fuels.

And burning it to generate   electricity or heat makes less air  pollution than something like coal. It also releases fewer pollutants like  nitrogen and sulfur oxides — pollutants   that contribute to unhealthy air  quality, and form smog and acid rain. But not everybody has the luxury of  clean air and lower-pollution energy.

Billions of people in low-income countries  don’t have access to natural gas. So,  they depend on high-polluting, solid fuels to  heat their homes and cook dinner, such as coal   or biomass. Biomass includes materials such as  charcoal, or wood, or dung from livestock.

These solid fuels release harmful chemicals when  burned, including the nitrogen and sulfur oxides   that make smog. And they contribute to four  million indoor air pollution-related deaths   each year. Let’s head to the Thought Bubble… Take a wintertime stroll through Ulaanbaatar,   the capital city of Mongolia, and you’ll notice the  chill doesn’t just nip at your nose.

It mauls it,   with an average January temperature of -20 degrees  Celsius. Oooh, delightful. I love the cold.

But before your nose goes numb, you’ll notice  the sting in your throat. A thick smog hangs   over the city, trapped at ground level by  cold winter air and surrounding mountains. That smog is full of teeny-tiny   soot particles called PM2.5.

These tiniest  of polluting particles are 30 times smaller in   diameter than a single strand of human hair. But they pack a mean punch. When someone   breathes them in and these particles get  lodged deep in the lungs and bloodstream,   they can cause pneumonia and bronchitis.

And Ulaanbaatar’s air can carry 20 times   more of these particles than what’s  considered safe to breathe. Coal is to blame here—Mongolia’s main energy  source. For many households, directly burning   coal is the only way to survive winter.

And coal  fuels 85% of the country’s power production,   so even electricity runs on it. Ultimately, Ulaanbaatar finds   itself in a coal-reliant cycle. Demand for coal drives more coal mining,   which sucks up groundwater and  dries grasslands to a crisp.

As grasslands disappear, nomads  are pushed to the city. And there,   they join the masses dependent on coal to stay  warm—which drives more demand for more coal. Thanks Thought Bubble!

Stuck in a loop like this, breaking up with coal  won’t be easy. Even replacing coal stoves with   coal-fueled electricity just pushes the  problem farther up the hill. Like passing   a sizzling ember from one hand to another.

Ow. When it comes to reducing   carbon emissions and making our world a  cleaner place for everyone, the situation   is messy, and heating is no exception. Increasing access to natural gas might help   Ulaanbaatar and other cities like it, but  it’s still a very complicated solution.

And as long as electricity runs on coal, bringing  electric heaters to more people won’t be enough   to see cities like this out of the smog—or  to see our planet out of rising emissions. Renewable energy, like solar or wind power,  would definitely help with this. But there’s   still another side of the equation we  haven’t talked about yet: cooling.

Quick: guess what’s on track to be the most  energy-consuming appliance in my house?   Based on my current rate of waffle consumption,  it feels like it should be my waffle-maker. But actually, it’s my air conditioner.  Back to my love of frigid temperatures. Air conditioners are heavy electricity  consumers, and it’s mostly fossil   fuels powering that electricity. Air conditioners also have a nasty   way of releasing hydrofluorocarbons, one of the  greenhouse gases with the longest name and the   most powerful global warming abilities.

But we can’t just ditch the AC altogether:   As the climate warms, the need  for air-conditioning rises, too. Billions of people are facing global warming’s  deadliest effects, including more frequent,   severe heat waves. To some, air-conditioning  becomes a life-or-death necessity.

The problem is, it’s a necessity that millions of people can’t afford,   so it’s also an issue of justice and equity. And to make things more complicated,   the same air-conditioning that helps people  survive blazing heat also exacerbates those   conditions in the first place. But it doesn’t have to be that way.

One thing governments can do is raise the minimum  efficiency requirements for appliances, so that   any new AC unit has to meet a certain standard. Moving away from hydrofluorocarbons, and towards   refrigerants with lower greenhouse warming  potential, would also help reduce emissions. And in fact, almost 200 countries have  already pledged to decrease the amount   of hydrofluorocarbons they use 80% by 2047.

Besides improving existing air conditioner designs   and scaling up carbon-free electricity sources,  another option to cool our homes is to ditch AC units altogether and consider other technologies. And as a big bonus, these solutions could help us with decarbonizing heating, too, and  even help us move away from natural gas. Take the heat pump.

Heat pumps use the same  basic mechanism of an air conditioner. When it’s warm out, both heat pumps and AC units  use heat-absorbing liquids called refrigerants to   move heat outside, so your bedroom stays cool. But heat pumps can also do the opposite.

In the  winter, they can bring in heat from the  cold air outdoors to keep your home warm. That might sound weird: I know when I’m out  waiting for the bus in January, here in the   Northern Hemisphere, my first thought isn’t,  “Oh, there’s so much heat in the air right now.” But for as cold as winter is, the refrigerant  in a heat pump is even colder. It can get down   to -50 degrees Celsius depending on the model.

So, the refrigerant absorbs and concentrates the   little bit of heat lingering in the snowy air,  which turns it into a gas. This refrigerant gas   is then brought inside and pressurized into a  warmer gas so that it can transfer the sweet,   sweet warmth of the air in your house. When powered by carbon-free electricity,   heat pumps emit almost no greenhouse gases.

And they can even have a negative Green Premium.   That’s the cost difference  between an energy source   that releases carbon and one that doesn’t. A negative premium means that, in some places,   it’s already cheaper in the long run to install  a heat pump than to run a natural gas furnace. That said, one barrier to heat pumps is that AC  units and natural gas furnaces last a long time.

It’s up to individual homeowners and building  developers to install heat pumps in the first place. And if my very expensive furnace  was still kicking, it would be hard for   me to get excited about forking over the  cash to replace it with a heat pump. Government tax incentives and loosening  building codes could be one way of   encouraging more people to make the switch.

But a third path to decarbonization is to   work with the systems we’ve got—and  find new ways of powering them. And for heating in particular,  there are lots of options. My favorite?

Trash. Now, unless you’re me or  a raccoon, it might seem like not much good can   come out of a steaming pile of trash. But the trash heaps in our landfills   already release gas as they decompose.  And that gas can be captured, converted,   and become a low-emission replacement for  natural gas in our existing furnaces.

Renewable “drop-in” fuels can  also help taper off emissions. These are basically fossil fuel substitutes made  from renewable materials, and they can step in   for natural gas in our heating systems. For example, second-generation biofuels   can be made from non-edible crops that are  already being produced alongside our food,   such as straw and corn husks.

Meanwhile, electrofuels go a step   further by not requiring crops at all. They’re made by capturing carbon dioxide   and mixing it with the hydrogen from  water molecules to create some of   the same molecules found in fossil fuels. Since electrofuels are made of hydrocarbons   just like traditional fossil fuels, burning them  would release carbon dioxide.

But because that   carbon was just captured from the atmosphere or  from a fossil fuel power plant, we wouldn’t be   adding any new emissions to the atmosphere. Then there’s the challenge of that pesky Green Premium. These drop-in fuels can also carry a  high upfront cost compared to fossil fuel energy.

By offering a renewable alternative, they can  help us reduce emissions as we wean our heating   systems off the fuels they were built for. Humans have devised ingenious ways of keeping   warm and staying cool, everywhere from the Arctic  Circle to the Mojave Desert. Unfortunately,   some of those energy choices have helped bring  us to our current mess: the climate crisis.

But that same ingenuity can  help us tackle the road ahead. It won’t be easy to decarbonize heating  and cooling. It will involve reducing the   emissions of existing systems, while  also working to create better ones.

But in the long run, electrifying heating  and cooling will be critical to reducing air   pollution and lowering greenhouse gas emissions. Achieving carbon-free heating and cooling won’t be   the only challenge. It’ll also be critical to  make it available to everyone on the planet.

The way we manage the temperature  indoors matters a lot. And,   as we’ll find out next time, so does the way  we — and our stuff — get from place to place. Special thanks to Eric Prestemon,  this episode’s thermostat monitor.

Eric, thanks for keeping an eagle eye on that dial,  and always turning the heat down when we leave   the studio—very energy conscious of  you. And thanks for being a supporter on Patreon. Crash Course Climate and Energy is produced by  Complexly with support provided by Breakthrough Energy and Gates Ventures.

This episode  was filmed at the Castle Geraghty Studio   and was made with the help of all these  nice people. If you want to help keep   Crash Course free for everyone, forever,  you can join our community on Patreon.