Carbon vacuum solves CO2 removal and warming.

The world has moved so slowly over the last 40 years to rein in greenhouse gases that scientists are now finding that cutting the use of fossil fuels alone may not be enough to stave off the worst effects of climate change. The world is on track for increasingly destructive heat waves, floods and storms. That means heat-trapping gases may also need to be pulled out of the atmosphere.

It's known as "carbon dioxide removal." In the latest international climate assessment, scientists found that using it will be "unavoidable" if countries are going to meet their pledges to keep average global temperatures from rising to ever-harmful levels.

Much of the technology to soak up carbon is still in its infancy. Some techniques can have significant impacts on the land. Some climate activists argue it's a risky distraction and that it would give the fossil fuel industry a free pass to keep operating.

Still, scientists running the numbers say the world has reached a point where every possible strategy is needed. Global emissions are still going the wrong direction. In 2021, they reached the highest level ever.

Why scientists say carbon removal is needed

To stave off extreme climate change impacts that could displace millions of people, scientific data shows that greenhouse gas emissions need to fall fast. Emissions need to drop 43% by 2030 and then fall to net-zero by midcentury, in order to limit warming to 1.5 degrees Celsius (2.7 degrees Fahrenheit).

Some solutions to cut emissions, like using renewable energy, are already widespread and cost-effective. But some emissions will be trickier to tackle. Farming produces emissions both from disturbing the soil and from the use of fertilizers, which provide food for soil microbes that release heat-trapping gases. The technology to create aircraft and oceangoing shipping vessels that don't produce emissions is still experimental. Some industrial processes, like steelmaking, require fuels that create extremely high heat.

How does carbon removal work?

Simply put, the idea is to absorb carbon dioxide emissions that have already accumulated in the atmosphere. Then, those emissions would be locked away in some kind of permanent storage, generally in underground geologic formations, so they don't escape to create more warming down the road. But despite carbon dioxide's power to heat the planet, it's very diffuse, making up less than 1% of the atmosphere. That makes it tricky to capture from the air in large quantities.

Option 1: Use nature to absorb carbon emissions

Nature is the most powerful carbon sponge around us. Plants take up carbon dioxide through the process of photosynthesis, locking it away in their tissues, making the world's forests, grasslands, soils and wetlands huge reservoirs of carbon. Building up these natural reserves could help slow warming, whether through planting forests, restoring wetlands and mangroves or encouraging agricultural practices that store carbon in the soil. This method is by far the cheapest so far. However, those ecosystems must be protected from development. If the plants and ecosystem are lost, the carbon escapes back into the atmosphere.

Option 2: Use leftover plants to make energy and capture the emissions

Plants are already used to make electricity in biomass power plants, which means that while that plant material trapped carbon, the carbon is released in the process of generating energy. A handful of biomass power plants are working on capturing those carbon emissions and then storing them in underground geologic formations. It's known as "bioenergy with carbon capture and storage."

The biomass used is often leftover material, like waste from agricultural crops, forest harvests or food waste, or it can come from crops grown specifically for that purpose. This strategy has the added benefit of producing electricity at the same time. But scaling it up could require more land, putting pressure on wild ecosystems that also store carbon and provide habitat for wildlife. It would take an estimated 115,000 to 166,000 square miles of land, as large as California, to grow the biomass needed to pull 1 billion tons of carbon dioxide out of the air.

Option 3: Pull it out of the air with big machines

Last year, the largest carbon removal project of its kind started up in Iceland. The Orca plant, run by the Swiss company Climeworks, is essentially a carbon vacuum. Fans pull in air, the carbon is captured by a special material and then it's pumped underground into geologic formations where it mineralizes, remaining trapped.

Other "direct air capture" plants, as they're known, are in development in the U.S. But most are still pilot projects. The technology is expensive and requires a lot of energy. One analysis shows that capturing a ton of carbon this way takes almost as much energy as burning 100 gallons of gasoline, which produces a ton of carbon. If the energy used isn't renewable, it would add more heat-trapping gases to the atmosphere.