Picture yourself driving a bus up a mountain. As you near the top, you can see the road on the downhill side—and you realize your brakes are broken. As the seriousness of the problem sinks in, you take your feet off the gas and swerve a bit to slow down. Had you slowed earlier in your climb, you might have been able to stop at the top, but now it is too late. You committed to going downhill. At least you are alive to make a last-ditch attempt to save yourself and the other passengers on board.

We find ourselves in a similar situation in the global efforts to address climate change. As manmade carbon dioxide emissions accumulate in the atmosphere, it is all but certain that concentrations will exceed safe limits, sending us over a tipping point without any brakes. Drastically reducing emissions will slow the speed of the bus, but that’s insufficient. Indeed, the fifth assessment report by the Intergovernmental Panel on Climate Change stated that any success in stabilizing climate change will require prolonged periods of negative emissions. This means that to mitigate the most severe effects of climate change, a carbon-neutral future isn’t enough—we need to pull back emissions from the past.

Geoengineering, or tinkering with the atmosphere to address problems we have caused, is an unfortunate term that includes very different technologies under a catchall umbrella for large-scale ways to not crash the bus and leave future generations with an unmanageable climate. In a 2015 publication, the National Academies of Science released two reports—using the synonymous but less controversial term “climate intervention”—on the topic, split into “carbon dioxide removal and reliable sequestration” and “reflecting sunlight into the earth.” Broadly speaking, the former connects the problem to the solution: too much CO 2 in the atmosphere causing climate change, therefore solutions involve methods to remove and sequester it. The latter considers addressing the symptoms of a warmer Earth: cooling the planet with modifications to divert sunlight.

But rather than dividing geoengineering approaches by type of technology, we should actually split the field into three different categories: the good, the bad, and the ugly. These categories are not based on the technologies that are used, but by their effects. Some technologies could be good, bad, or ugly, depending on how they are implemented and how they continue to be developed.

The Good

Good geoengineering motivates the bus driver to take his foot off the gas with the confidence that he can stop in time. It would be a “technological fix,” which means that it 1) connects the problem (too much carbon dioxide in the air) to the solution; 2) creates measurable and unambiguous outcomes (for instance, we can measure the amount of carbon dioxide that the technology removes from the air, and we know how much CO 2 needs to be removed to offset emissions); and 3) allows for future research and development that will lead to significant cost reductions. A technological fix would allow humanity to clean up after itself without causing an additional mess.

For instance, researchers are investigating technologies that would, for instance, allow us to remove CO 2 from the atmosphere to be permanently stored. (I work at Arizona State University’s Center for Negative Carbon Emissions; ASU is a partner with Slate and New America in Future Tense.) The logic is straightforward: If a ton of carbon dioxide is emitted, then a negative emission or offset is needed to put that ton away.

Good geoengineering would have the potential to scale, and scientists would fully understand the environmental effects and energy use. If the approach disrupts other systems or natural ecosystems, causes negative consequences, consumes land that might be needed for food production, or weakens support for reducing carbon emissions, it is not good and should not be undertaken. Good geoengineering would not be an easy fix, nor would it be expected to immediately reduce the pain that is felt from a warmer climate. It would be undertaken in conjunction with emissions reductions—it would not be a crutch.

The Bad

Bad geoengineering might seem more attractive once the bus is rolling and accelerating downhill. It is a quick and (usually) cheap fix and allows any individual actor, be it a country or a rogue billionaire, to operate independently. It also doesn’t really solve the problem but rather tries to treat the symptom. For instance, solar geoengineering seeks to reduce the amount of sunlight that warms the Earth at the surface, troposphere, upper atmosphere, or even space level. The planet might cool, but this would require the continued treatment; it would be difficult to stop once started. Meanwhile, people would continue to freely dump CO 2­ into the atmosphere.

The Ugly

Ugly geoengineering might add brakes but could make the bus lose a wheel. Negative emissions could be ugly geoengineering if additional problems emerge when the technologies are brought to scale (or if they are unable to scale). An ugly approach to geoengineering would be masked in ambiguity and treat negative emissions as secondary to providing energy. For instance, consider bioenergy with carbon capture and storage, or BECCS. This approach burns biomass—like wood—at a centralized plant to make energy, and then the resulting carbon dioxide is captured and stored. The Intergovernmental Panel on Climate Change suggests it as an approach to negative emissions, but it’s ugly because not all biomass is created equal, and if used as a form of geoengineering, it would require significant amounts of land and water. That might end up releasing more carbon dioxide in the air if it upsets existing biomass or ecosystems or take over arable land needed for food production. Likewise, iron fertilization might increase the uptake rate of carbon in the oceans but could cause massive algae blooms.

What shouldn’t qualify:

Some of the things that people call “geoengineering” shouldn’t really be considered such at all because they do more than just combat climate change. For instance, biochar—a technology, more than a century old, to create energy by burning wood and starving it of oxygen—is a great form of carbon-negative energy that can also have added benefits when applied to soils. Similarly, soil techniques that allow for negative carbon not only remove CO 2 from the atmosphere, but also create a number of positive co-benefits for healthier crops.

Another approach that should not be considered geoengineering is removing carbon dioxide from the atmosphere with direct-air capture technologies for utilization—that is, technology that takes out the CO 2 and then recycles it, whether for foods, fuels, or fibers. These direct-air capture techniques should consider the value of having a source of readily available carbon that is not fossil-based and can play a major role in accelerating a pathway to a carbon-neutral future.

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As the world looks to make investments in technologies that might play a role in keeping the bus safe on the road, it is helpful to ask a few questions. Do we clearly understand the costs and benefits? Are we sure that it will not cause problems that weren’t there before? Does it connect the problem to solution, rather than just offering a Band-Aid? If the answer to all of these is yes, then it’s good—and we are probably better off just calling it a form of carbon management or negative emissions, not geoengineering. Let’s leave that for the bad and ugly.

This article is part of the geoengineering installment of Futurography, a series in which Future Tense introduces readers to the technologies that will define tomorrow. Each month from January through May 2016, we’ll choose a new technology and break it down. Read more from Futurography on geoengineering:

Future Tense is a collaboration among Arizona State University, New America, and Slate. To get the latest from Futurography in your inbox, sign up for the weekly Future Tense newsletter.