You've seen the headlines about capturing carbon dioxide from smokestacks or the air. It feels like a win. But then a practical, nagging question hits: what do we actually *do* with it? Tucking it away isn't as simple as putting a box in the attic. The journey of captured carbon splits into two distinct, and sometimes competing, pathways: putting it to use, or putting it away for good. Most people don't realize that the choice between these paths defines the technology, cost, and ultimate climate impact. Let's trace that journey, from the capture point to its final destination, and cut through the hype to see what's working on the ground today.

The Fork in the Road: Use It or Store It?

Once CO2 is separated and purified, it faces its first major decision. This isn't just philosophical; it dictates the infrastructure, business model, and regulations for the next 50 years.

Utilization (Carbon Capture and Use - CCU) treats CO2 as a feedstock. The goal is to transform it into a product that has economic value. Think of it as recycling carbon. The big appeal here is creating a market—someone might pay for this CO2, offsetting the high cost of capture. The catch? If the product (like fuel) is burned later, the CO2 goes right back into the atmosphere. It's a delay, not a deletion, unless the carbon is locked into a durable material.

Sequestration or Storage (Carbon Capture and Storage - CCS) treats CO2 as waste. The goal is permanent isolation from the atmosphere. This is the climate mitigation heavyweight, responsible for the vast majority of captured carbon volumes today. There's no direct product revenue, so it often relies on government incentives, carbon taxes, or regulations to make financial sense. The peace of mind comes from permanence.

Path One: Giving Carbon a New Job (Utilization)

This is where chemistry gets creative. Not all uses are equal. We can categorize them by how long they keep the carbon out of the air.

Short-term Cycling (Months to a Few Years)

These uses typically involve re-releasing the CO2 soon after.

• Enhanced Oil Recovery (EOR): This is the elephant in the room. For decades, the largest market for captured CO2 has been pumping it into aging oil fields to squeeze out more crude. It's controversial because it enables more fossil fuel production, but it also provides a revenue stream that has funded much of the early CCS infrastructure. About 70-80 million tons of CO2 are used for EOR annually in the US alone, primarily from natural underground CO2 deposits, but increasingly from industrial capture.
• Production of Fuels and Chemicals: CO2 can be combined with green hydrogen (from renewable electricity) to make synthetic methane, methanol, or even aviation fuel. Companies like Carbon Engineering are piloting this. The problem is the staggering amount of clean energy needed. Making one barrel of synthetic jet fuel requires about as much electricity as an average US home uses in a month. It's not scalable without a massive, cheap surplus of renewables.

Long-term or Permanent Lock-up (Decades to Millennia)

These are the utilization champions for climate goals.

• Building Materials: This is the sleeper hit. CO2 can be mineralized and turned into a solid. Companies like CarbonCure inject liquefied CO2 into fresh concrete, where it reacts with calcium ions to form nano-sized limestone particles, strengthening the mix and permanently embedding the carbon. The CO2 becomes part of the building's foundation, bridge, or sidewalk for a century or more. Other companies make carbon-negative aggregates from waste CO2 and industrial by-products, replacing mined gravel.
• Polymers and Plastics: Some specialty plastics, like polycarbonates, can use CO2 as a building block. Covestro has a plant in Germany using CO2 to make foam for mattresses and upholstery. The volume is small but the value is high.

Path Two: Permanent Retirement (Sequestration)

This is the bedrock of climate scenarios from the International Energy Agency (IEA) and the IPCC. The logic is simple: put it back where it came from—geological formations deep underground.

Geological Storage: The Main Event

We're talking about injecting supercritical CO2 into porous rock layers over 1 km deep, capped by impermeable seal rocks (like shale or salt).

• Depleted Oil and Gas Reservoirs: These are well-understood. We know they held hydrocarbons for millions of years, so they should hold CO2. The infrastructure (wells, seismic data) is often already there. The Sleipner project in the Norwegian North Sea has been injecting about 1 million tons of CO2 per year into a saline aquifer since 1996, monitored as a global test case.
• Deep Saline Formations: These are vast, porous rock layers filled with salty water. They offer the largest potential storage capacity globally, by far. The Illinois Basin – Decatur Project in the US is a flagship example, storing CO2 from a biofuel plant.

Mineral Carbonation: Turning CO2 to Stone

This isn't just storage; it's transformation. The Carbfix project in Iceland dissolves captured CO2 in water and injects it into basaltic rock. The CO2 reacts with calcium and magnesium in the basalt to form solid carbonate minerals—literally turning to stone within two years. It's incredibly permanent but requires specific geology and water.

The Hidden Middle: Transport & The Logistics Nightmare

Nobody gets excited about pipelines and ships, but this is the make-or-break. Captured CO2 is compressed into a dense, supercritical fluid for efficient movement.

Pipelines are the workhorse. The US has over 5,000 miles of CO2 pipelines, mostly for EOR in the Permian Basin. Building new ones for dedicated storage faces massive NIMBY (“Not In My Backyard”) opposition and regulatory hurdles. A single lawsuit can delay a project for years.

Shipping is emerging for regions without pipeline networks. CO2 is chilled into a liquid and transported in insulated tanks, similar to LNG. This is key for countries like Japan or in Northern Europe looking to ship CO2 to offshore storage hubs in Norway or under the North Sea.

Here's a real struggle: if you're a small or medium-sized emitter (a cement plant, a bio-refinery), you can't afford to build a dedicated pipeline hundreds of miles to a storage site. You need a shared “CO2 highway” system, a collective infrastructure that doesn't fully exist yet. This “last-mile” problem is what keeps many industrial CEOs up at night when they consider carbon capture.

Your Top Questions on Captured Carbon, Answered

So, what happens to carbon after it's captured? Its journey is neither simple nor singular. It can become part of your future driveway, get locked away in ancient rock layers a mile below the seafloor, or, in many cases today, be used to extract more oil—a complex trade-off. The path it takes depends less on technology and more on cold, hard economics, evolving policy, and the difficult, unglamorous work of building infrastructure. The capture is just the first step. The real story is what comes after.