We often hear talk about reducing emissions, cutting back on fossil fuels and switching over to green energy sources like solar panels or hydroelectric. But that’s only half the battle. 

According to a 2018 report from the Intergovernmental Panel on Climate Change, all scenarios for limiting the rise in global temperatures to 1.5 degrees Celsius depend upon the use of negative emissions technologies, more conveniently called NETs. So what exactly are these NETs, and how can we use them to slow global warming?

The term describes a wide range of techniques for pulling carbon out of the atmosphere and either storing it elsewhere or making use of it. NETs range from naturalistic solutions, like restoring carbon-storing peat bogs or planting more trees to suck carbon from the air, to more high-tech alternatives, like the carbon capture, utilization and storage systems — commonly called CCUS — that president-elect Joe Biden has included in his environmental plan. 

An especially promising subset of CCUS is called bioenergy with carbon capture and storage, and involves burning plant matter for energy, then capturing the carbon emitted by that plant matter and rerouting it underground, where it can act as fertilizer for more plants. Unlike some other CCUS models, this method doesn’t produce excess carbon that requires storage, keeping it all in a closed, energy-producing cycle.

There are so many cool NETs that it’s difficult to list them all. Adding alkali to the atmosphere or the ocean could speed up the rate at which water, whether vapor or liquid, absorbs carbon dioxide to make carbonic acid. Though this one sounds pretty rad, scientists are not yet sure what other impacts it could have on the environment.

Another possibility, with a very mystical name, is biochar. Unlike the coal we burn for fuel, biochar is produced by burning biomass in a controlled environment without oxygen. This process essentially locks the carbon contained in the biomass in place for hundreds of years, and the biochar can then be used to improve soil fertility. Considering that this process doesn’t produce unusable waste and it gives off biofuel as a byproduct, biochar ranks among one of the better options for carbon sequestration. Even then, scientists have some concerns — biochar darkens the soil, meaning that the earth will warm more quickly, and, according to one study, it has the potential to simply dissolve and wash into the watershed.

A more naturalistic proposition comes in the form of enhanced ocean productivity, in which scientists infuse parts of the ocean with the nutrient iron, which would set off the growth of phytoplankton. Just like trees and other plants, phytoplankton take in carbon from their surroundings, allowing more carbon to enter the ocean from the atmosphere. When the plant dies, it would simply fall to the bottom of the ocean, where its carbon-filled skeleton would lay for many, many years. Like all other NETs, enhanced ocean productivity still has its downfalls — it could be difficult to navigate international regulations on oceans, and the large-scale impact on the marine environment remains unknown.

You might be noticing a pattern here. Though scientists have many ideas for potential NETs, so much uncertainty surrounds the actual execution of these techniques. Often the implementation of NETs is limited by available land, environmental concerns and cost. For instance, bioenergy with carbon capture and storage could cost from $100 all the way up to $400 per ton of carbon sequestered. Considering that, according to estimates, about 10 billion tons of carbon will need to be stored by 2050 in order to reach the Paris Climate Accord’s goal of limiting global temperature rise to 1.5 degrees Celsius, that’s a pretty heavy price tag.

In addition to the logistical concerns, NETs could encounter bureaucratic difficulties because of the massive scale most of them require in order to make an impact. Many governments could only implement such schemes on a regional or national level, barring unprecedented international cooperation, and if some governments choose to ignore the growing threat of climate disaster, there’s not much others can do despite the global nature of the problem.

The good news, though, is that there are so, so many ideas, from restoring shoreline ecosystems to optimizing farming techniques for carbon sequestration, from direct-air capture — sucking the carbon directly out of the atmosphere — to using plant-based materials in buildings in order to keep that carbon locked away. When I think of combining all these different methods of capture and storage, that goal of 10 billion tons doesn’t look quite as preposterous. 

Even with the difficulties, there’s no denying that we need both emission reduction and NETs working simultaneously in order to prevent disaster. As Stephen Pacala, professor of ecology and evolutionary biology at Princeton University, tells Yale Environment 360, we have dallied on the problem of climate change long enough that we can no longer delay on either of these fronts.

“Humanity keeps procrastinating on mitigation and so it becomes impossible at some point to meet the safe or declared target of limiting temperature increases to 1.5 to 2 degrees [Celsius] without negative emissions,” Pacala said. “That’s sadly where we are now.”

Sad indeed, but not without hope. We still have a chance to pull back from the precipice if we start right this very second. The U.S. government has already allocated $60 million for NET research, and hopefully will continue such efforts. Note, although NETs are undeniably important, the potential impact of NETs does not lessen the need for emission reduction efforts. While you might not be able to do much to implement NETs in your daily life — other than plant some trees once you manage to get your own patch of land — you can express their importance to your local representatives, alongside starting or continuing your own emission reduction efforts. Stay hopeful out there, my friends.

Sarah writes primarily about trees, climate change and walking. You can reach her at [email protected].