News•April 20, 2017

A Cooler Future May Hinge on Removing CO2 From the Air

Climate pollution equal to about 27 times humans’ 2015 carbon dioxide emissions may have to be removed from the atmosphere and locked underground forever in order to keep the globe from warming beyond 1.5°C (2.7°F) above preindustrial levels, according to a new study.

The research, led by scientists at the International Institute for Applied Systems Analysis, or IIASA, in Austria, adds to the mounting evidence that countries will have to physically remove carbon dioxide from the atmosphere to prevent global warming from exceeding dangerous levels.

An oil refinery in Deer Park, Texas.
Credit: Roy Luck/flickr

Removing carbon dioxide from the atmosphere is called “negative emissions,” and it’s central to the Paris climate agreement, which aims to prevent the globe from heating beyond 2°C (3.6°F). One of the main goals of the agreement is to keep warming to 1.5°C, a goal growing more difficult as the U.S. and other countries waver on their commitments to cut emissions.

Human greenhouse gas emissions will have to peak globally within 10 years for the 1.5°C target to be met, according to the study.

“Emissions need to peak very soon because the CO2 emitted now doesn't disappear, or stop trapping heat, even if we were to reach full decarbonization,” said the study’s lead author Brian Walsh, a former IIASA researcher now consulting for the World Bank. “Emissions need to not only peak but begin a rapid decrease soon in order to have a plausible shot at meeting the 1.5°C target.”

Turning emissions around so quickly will involve humans completely weaning themselves from fossil fuels use by around 2050 and widely implementing negative emissions techniques, Walsh said.

Glen Peters, a global carbon cycle researcher at the Center for International Climate Research in Norway, who is unaffiliated with the study, said emissions need to fall as fast as they have increased in recent years, something that will take ever-more heroic efforts if climate pollution is to peak within a decade.

“It’s hard to see 2°C without some sort of negative emissions,” he said.

The study suggests that as fossil fuels are phased out, people may have to remove and permanently store an exagram of atmospheric carbon dioxide, or roughly 27 times the carbon that humans emitted in 2015. Globally, humans emitted about 36 billion metric tons of carbon dioxide that year, according to European Commission data.

But the researchers say that negative emissions on such a large scale “remains a distant reality.”

Most computer models forming the basis of the Paris pact’s emissions cuts assume that humans will be actively removing carbon dioxide from the atmosphere on a large scale by late this century. But much of the technology that would reduce atmospheric carbon concentrations is in its infancy, has never been proven to work on a large scale and the hazards associated with it are largely unknown.

Negative emissions techniques under development include directly capturing emissions and storing them underground, planting more trees to store carbon dioxide in their trunks and roots, and, among other methods, engineering forests to store more carbon than they would naturally.

Air pollution in Toronto.
Credit: United Nations/flickr

The technique the IIASA study considers most promising is called “biomass energy with carbon capture and storage,” or BECCS. That technique involves growing trees and plants on a large scale to be burned in biomass power plants whose carbon emissions would be captured and safely stored underground.

BECCS and other methods requiring planting large new forests are controversial because it’s unclear how they would alter ecosystems, displace people and be effective in actually cutting emissions. Some scientists have called the potential risks a significant “moral hazard,” while others pointed to research showing that cutting down trees to burn as biomass energy does nothing to remove carbon dioxide from the global carbon cycle.

The study says that if BECCS and other negative emissions technologies prove to be uneconomical or unfeasible, the only alternative is for people to completely stop using fossil fuels as soon as possible.

But Peters said countries’ ability to develop negative emissions technology quickly enough to make a dent in climate pollution is doubtful.

“At the moment, it’s hard to see a business model and pathway that would make negative emissions technologies feasible at scale,” Peters said.

“These are big technologies in that it takes time to plan, approve, and build the capture facilities, not to mention the time and logistics to characterize carbon storage sites,” he said. “These time lags would suggest the large scale roll out would not happen for 10 years even if we started planning today. Even if we figure out the technology in the next decade, then it may be too little too late, unless we have deep mitigation already ongoing.”

But Walsh said that when societies have accepted the full costs of emitting carbon, including the social cost of carbon and the costs of measures to cut climate pollution and develop negative emissions technology, they’ll begin to pour more money into finding ways to reach the Paris targets.

“It could be that we’re nearing a tipping point in terms of climate change consequences and public understanding thereof,” he said. “And when we get there, I have no trouble believing the policy, funding and technology will follow quickly.”