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MIT Technology Review

Here’s how we could go carbon neutral in 25 years

The real trick is putting biowaste to work.

January 30, 2020
A rotten apple.A rotten apple.
A rotten apple.
Photo by Andrew Johnson on Unsplash

In the fall of 2018, as California governor Jerry Brown’s final term was winding down, he signed an executive order that set an audacious climate goal: the world’s fifth-largest economy needed to become carbon neutral by 2045.

That means the state will have to remove enough greenhouse gases from the atmosphere to balance out whatever amount its residents and businesses are still emitting 25 years from now.

But many wondered whether California, or any other major economy, could actually stop adding to the greenhouse gases driving climate change with the technology we have today. In a study released Thursday, researchers at Lawrence Livermore National Lab determined the answer is yes.

“We do have to do an enormous amount of development. We have to scale up,” says Roger Aines, a coauthor of the report who leads the lab’s Carbon Initiative, a research program on carbon dioxide removal. “But we don’t have to invent new things.”

While the technological particulars would differ, Aines says that also means most nations and major regions could likely become carbon neutral with the tools we have today.

The big challenge in achieving that goal is that while we more or less know how to eliminate emissions from the electricity sector, there are still big parts of the economy where we don’t have available and affordable options. That includes things like aviation, shipping, and cement production. And the world is still puzzling over what to do about all those methane-burping cattle and sheep.

So to meet the 2045 deadline, California would need to begin implementing a number of technologies that barely exist today, including machines that suck CO2 out of the sky, and methods of converting dead trees and other forms of carbon-rich waste into clean fuels likes hydrogen.

The new study estimates California will need to remove at least 125 million metric tons of carbon dioxide per year by 2045. The authors conclude this can be done for less than $10 billion a year, about 0.4% of the state’s annual GDP.

Carbon recycling

Around 25 million tons could be taken care of by restoring forests and altering soil management practices in agriculture to absorb and store more carbon. Another 16 million could be removed by direct-air capture machines and stored permanently underground in geological sites in the state’s Central Valley.

But the bulk of emissions reductions, 84 million tons a year, would come from waste biomass, including agricultural by-products, food waste, livestock manure, human sewage, sawmill residue, and trees removed from forests.

The report found the biggest opportunity would be to use this biomass to create hydrogen, a fuel that doesn’t emit any carbon dioxide when it’s used.

It could be made through a multistep procedure, known as gasification, that uses high temperatures in a low-oxygen environment to break down organic materials without full combustion. In the end, it produces carbon dioxide that can be captured and stored, as well as hydrogen that can power specialized vehicles or generate electricity directly in certain types of turbines. Hydrogen, which is typically derived from natural gas through a method that produces considerable CO2, is also used heavily in various industrial processes.

Challenges

But there’s often a big gap between what appears technically feasible and what we can pull off in the real world.

For one, Carnegie Institution researcher Danny Cullenward warns that the three major levers in the plan—land use, direct air capture, and hydrogen from biomass—are all “untested at scale.” He adds that the study may overestimate how cheap direct air capture will become and how much carbon the state’s forests and soils are likely to store. After all, in some recent years, including the major wildfire season of 2018, California’s forests have produced more carbon dioxide than they absorbed.

Cullenward also says reaching carbon neutrality presumes that California will achieve its goals in cutting emissions from electricity, transportation, and other sectors we know how to clean up. At the current rate of reductions, however, the state will miss its 2050 decarbonization target by a century.

Holly Buck, a fellow at the University of California, Los Angeles, who focuses on carbon removal issues, agrees with the broad conclusions of the report. But she says it will require major changes in infrastructure, processes, and behavior to collect and transport this amount of biomass waste from cities and sectors across California. And it could be very difficult to get communities on board with all the plants, pipelines, and CO2 storage envisioned, in a state where building any major projects is a struggle.

Aines agrees there are big hurdles.

“We know it will cost money,” he says. “We know it will require changes in attitude. But we can do it—and it’s time to do it.”