The Case for Carbon Removal

In 2016, the earth’s atmosphere surpassed 400 parts per million (PPM) of carbon dioxide. The last time similar concentrations were present, the planet’s temperature was a few degrees warmer and sea levels were dozens of meters higher than today. Humans were still many millions of years away from making an appearance on the evolutionary stage.

Today, average temperatures are roughly 1.5 degrees warmer than they were during the preindustrial period. After a short stretch of years during which annual emissions declined, 2017 once again saw an overall net increase, signaling an unwelcome trend that is projected to continue into the near future. In spite of global accords such as the Paris Agreement and other commitments around the world, there is receding hope that we will consistently return to under 350 PPM, the level that consensus science agrees is necessary for maintaining climate stability.

As the rate and consequences of climate change accelerate, it’s strange how little we’ve considered one simple fact: eliminating new emissions is no longer sufficient to prevent climate catastrophe. This reality dictates that we must rapidly determine and deploy ways of removing and relocating giga-tons of carbon from the air each year.

A growing number of “negative emissions” technologies that could achieve this at scale have recently emerged: Carbon capture and sequestration (CCS) and BECCS (“bio-energy with carbon capture and storage”) are the most widely discussed and anticipated among these options—but additional solutions have arrived or are on the horizon. These include a host of direct air capture (DAC) technologies, which chemically pull carbon from ambient air and convert it into more stable forms. It could then be recycled into fuel or other materials. Other approaches seek to leverage and enhance the carbon-sink capabilities of forests, soil, silicate and certain geological formations.

That these technologies will ultimately become widespread, in one form or another, is an important assumption embedded into the math of the Paris Agreement. But within the broader discourse on climate solutions, they remain somewhat controversial and largely overlooked by many of the most influential experts and activists. As a result, general public opinion and understanding of the need to remove carbon from the atmosphere is woefully underdeveloped—right at a time when our collective attention is most essential.


Common arguments raised against negative emissions solutions often relate to cost and technical hurdles. It is regularly asserted that negative emissions technologies are not the lowest-cost option for confronting climate change and that cheaper, more mature solutions therefore must be exhausted first.

This argument assumes that carbon removal and carbon mitigation are different means to the same end. This is not the case, as mitigation techniques like energy efficiency and clean energy serve an entirely different purpose than do negative emissions technologies. The job of the latter is to recycle and modify the carbon content of current and future atmospheres. Energy efficiency and renewable energy do not and cannot perform that function alone.

And critiques based on current and projected cost and technical performance simply cannot account for the unpredictable nature of technological innovation. We’ve seen numerous examples of this in the past decade and have even gained fundamental lessons from the history of renewable energy (particularly solar and wind). Past projected rates of penetration and cost reduction were consistently and often wildly off the mark. Why? Because it is impossible to know the trajectory that innovation will take, and when and where breakthroughs will occur.

But in spite of resistance, negative emissions technologies are taking shape in interesting, exciting ways that should inspire cautious hope rather than apprehension. On May 30, Urban Green will host Cities and the Future of Negative Emissions, a panel discussion that will explore these unfolding developments with a specific lens on the role that urbanism might play in advancing progress.


Emissions reduced or removed anywhere help address the global problem everywhere, so it is reasonable to assume that implementation—particularly for land-intensive applications—should be carried out wherever it is cheapest and easiest to do so. The barriers for implementation in dense and expensive cities are obvious. However, as centers of innovation, inspiration and ingenuity, cities possess critical ingredients to catalyzing progress.

During a related panel that Urban Green hosted last year, Capturing Carbon in Urban Soil: What’s Possible In Cities, soil scientist Peter Groffman pointed out that although cities have less soil–and therefore soil sequestration potential—than rural areas, it is in cities where he encounters the greatest level of enthusiasm and where some of the most promising and creative experiments are taking place.

With this exciting potential in mind, Urban Green’s upcoming discussion will explore both the implementation and creative potential of negative emissions from a variety of perspectives, including design and public policy. We hope you will join and contribute to the conversation.

About the authors

Chris Neidl
Christopher Neidl is a clean energy policy advocate, educator and project advisor with thirteen years of experience facilitating on-grid and off-grid clean energy adoption in the United States, Asia and Africa.