The United Nations Intergovernmental Panel on Climate Change estimates that warding off catastrophic global warming requires actively removing 100 billion to 1 trillion tons of carbon dioxide from the atmosphere by midcentury. Planting billions of trees is one way of doing this, but there are also a few promising demo-ready projects that are trying to remove carbon. There’s active air capture technology, which is being shown off in Iceland where carbon dioxide is being captured and injected underground to bind with basaltic rock, which can hold it indefinitely. Then we have passive air capture technology where resin absorbs CO2 from the air when dunked in water. Meanwhile, in Canada, a company is using renewable energy to turn air-captured CO2 into fuels like gasoline and diesel—which doesn’t sound too promising. However, the company does say its tech can also capture CO2 for permanent storage. Another promising technology being utilized in Illinois takes CO2 from industrial exhaust plumes and turns it into renewable biofuels. In essence, this can result in negative emissions if the facility runs on renewable biofuels. Last but not least, there’s blue carbon restoration. So-called blue carbon, the CO2 stored in coastal ecosystems such as mangroves and salt marshes, is 10 times as dense as carbon stored in forests. Last fall, Apple Inc. announced it had invested an undisclosed sum in a Conservation International project to protect and restore 27,000 acres of mangroves in Colombia, which is expected to capture 1 million tons of atmospheric CO₂.