In the waning days of the 2020 election, President Trump ran ads that centered on "fracking." Trump asserted that if Joe Biden won, he would ban the practice—a claim that Biden denied.

What is fracking? The word is short for "hydraulic fracturing," a process by which liquids are pumped deep underground at high pressure so as to break apart rock beds break, releasing oil and gas.

Trump's ads aimed to win over swing-state voters in Pennsylvania, which is second only to Texas in the amount of natural gas extracted. It's not clear how effective a strategy this was, though; some polls suggest that a slim majority of Pennsylvanians might oppose fracking. (In case you somehow missed it, Trump lost the state, and also the election.)

Critics say fracking is a nasty practice that should be banned; proponents suggest it's actually helped fight global warming. So what's the truth? Here's the full scoop.

How does fracking work?

Fracking targets "unconventional reservoirs" of oil and gas, which is an industry phrase used to describe supplies that earlier technologies could not tap. There are various such reservoirs, often distinguished by the kind of surrounding rocks. Shale gas—which, as the name implies, is natural gas trapped inside shale rock—is among the most common.

The idea is to drill downwards—sometimes as deep as a mile—to create a well, into which liquid is injected. The liquid is at a high-enough pressure to break open fractures in underground rocks, which allows trapped gases and liquids to pour into the well. This is why the techniques is called "hydraulic fracturing," which is often shortened to fracking.

This is actually an old technique—first conducted experimentally in 1947 and applied commercially within a few years. But it has been updated along the way, first by using larger volumes of liquid. A major breakthrough came in the 1980s: horizontal drilling, in which the drill is turned ninety degrees once it hits a reservoir. Since rock layers generally lay in horizontal layers, this allows the drilled hole to access more deposits.

Fracking targets otherwise-hard-to-reach deposits of oil and gas, breaking apart rocks that would otherwise trap the fuel.

The liquids used have changed, too. (And vary from place to place today, since different rock beds have different properties, and require different treatment.) Often, the liquid now consists of "slickwater," or water mixed with sand and  chemicals. The sand (which is sometimes replaced with a synthetic solid of similar size) is called the "proppant," and wedges into existing fractures, forcing them to open into wider cracks. The chemicals are intended to decrease friction, helping create fractures further away from the well bore.

What is its status today?

For decades after hydraulic fracturing was invented, the technique contributed little to the world's fuel supplies. Then, in the early 2000s, fracking took off, in part thanks to small oil firms tinkering, seeking a way to compete with larger companies. Fracking now accounts for the vast majority of oil and gas recovered in the U.S.

That helped the U.S. set records for fossil fuel production in 2018 and 2019. The country now leads the world in the production of both oil and gas. At this point, in fact, there is so much gas that prices have plummeted, which is hurting some fracking companies. The fracking boom is also fueling the rise of plastics, which are produced from petroleum. Over the next decade, plastic production is predicted to increase by 40 percent.

A "play" in the world of oil and gas is a group of reservoirs in a single region that share the same geological conditions. The major U.S. fracking play is the Permian Basin in Texas. The state produces 41% of U.S. crude oil and 24% of U.S. natural gas. The Marcellus Shale in Appalachia is another major play, and is the largest single source of natural gas. This is the formation that Pennsylvania wells target.

New York banned new fracking wells in 2010, though natural gas is still produced from wells that had been drilled before the ban went into effect. In 2017, Maryland also banned fracking. (Vermont and Washington also have bans, but these are largely symbolic, since neither state has deposits that could be accessed through fracking.)

The U.S. has been the innovator when it comes to fracking, and remains the clear leader. But other regions are pursuing this technology, too, including Canada and, increasingly, China. In Europe, meanwhile, many countries have banned the practice over concerns about its environmental impact.

Why do people like fracking?

Fracking's big appeal comes down to money. One study found that the boom in fracking helped to create more than 700,000 jobs in the late 2000s and early 2010s, and perhaps millions more in supporting industries. The fuel produced has also kept prices for gasoline and electricity low in the U.S.

The economic impact of fracking is undeniable, at least for the moment.

It's not just money, though: The increase in fuel production gives the U.S. political power, too, as it can apply sanctions against countries (like Iran or Venezuela) from whom it might otherwise need to import fuels.

Why are people opposed to fracking?

Though fracking brings in a lot of money, it does a lot of damage, too. A single well can require as much as 16 million gallons of water—what a city of 50,000 people might use in a day. Some of that water, tainted with chemicals, can leak back to into freshwater supplies. Three million gallons leaked into a creek in North Dakota, for example, and the EPA has struggled to quantify the full extent of this problem.

Fracking has also been blamed for a surge in earthquakes, especially in Oklahoma and Ohio. When it comes to earthquakes, the biggest problem is not the drilling itself, but rather the storage of waste waster. Often, it's pumped underground, which causes pressure changes that lead to shifts along fault lines.

As the fracking boom took off, Oklahoma began to see as many or more M3 earthquakes than California, a typically much more seismic state. (A magnitude 3 earthquake is large enough to feel.)

In addition, many people find fracking operations to be, well, ugly. There are pipelines and lights; endless noises and flaring towers. (And the gases released cause air pollution problems: studies suggest fracking has led to low birth weights in nearby communities). The jobs produced by fracking don't always last; eventually the oil or gas is tapped and the industry moves on—turning former "boomtowns" into ghost towns.

What is its impact on the climate?

Many people also worry that fracked fuels are contributing to climate change.

Fracking proponents, though, claim the opposite. As oil companies turned to fracking in the 2000s, U.S. emissions—which are higher per capita than anywhere besides China—began to decrease. And some of this fall can be credited to fracking. As natural gas production picked up, the price dropped, making it a much more appealing fuel source than coal. Per unit energy, gas has half the emissions of coal.

Natural gas has another asset, too: It is very easy to turn on or off the flow into a plant. That means gas-fueled power plants can be quickly powered up or down. This may prove quite useful in a world that relies on extensive solar and wind power, resources that are inconsistent.

Natural gas plants may help make up the difference when the sun is down or the wind is calm. Some analysts believe the two technologies have grown hand in hand: that the rise of fracking has helped bring down the price of renewable energy. That said, there may be other, greener options for this niche. Perhaps a new generation of nuclear plants will work to steady out renewables; perhaps we will develop effective forms of battery storage. (Even if if natural gas plants are outfitted to capture emissions, leaking pipelines is a major and under-examined source of emissions.)

Natural gas can supplement renewable energy, though emerging solutions may offer a lower-emissions replacement for this role.

Since fracking's great asset is the way it's brought down fuel prices, we should note the built-in downside: Cheap fuel makes it easier for us to use more and more energy—and not just electricity. Transportation is now a larger source of U.S. emissions than electricity, and the price of gasoline—also kept low by abundant fracked petroleum—gives us no reason to stop driving.

Analysts have found that if we burn through all of the oil and gas that we've identified, there will be no way to keep global warming below 1.5°C. Natural gas is far from a zero-carbon resource: Half the emissions is not the same as none. And at this point, the goal has to be none.