Negative emission technologies?

Carbon dioxide levels continue to climb; the planet is getting warmer.

It is an anxious time for those who understand the threat. The Paris Agreement was an unprecedented display of international solidarity and resolve, but actions speak louder than words—and the action up until now is far too modest and frankly insufficient.

The recent Climate Action Tracker update [1] calls out the countries that are lagging behind—either because they set their sights too low, or because they haven’t moved fast enough to achieve what they set out to accomplish. Either way the result is the same. Slow motion mitigation.

CAT scan

The CAT report looked at 24 countries responsible for 80 % of emissions.  It found that 24 governments have set insufficient targets; of these, 16 governments have implemented policies that will not even result in achievements of their targets. Only seven governments have set targets compatible with the 1.5°C or 2°C limits and of these, four are not backed up by sufficient policy action.  Canada’s NDC rating is ‘Highly insufficient’.  The USA, not unsurprisingly, is worse.

In other words, after all the jubilation in Paris subsided, and the participants returned home, the uncomfortable truth is that global action to stop and reverse the trend towards a hotter planet has largely failed.

Even if the current set of Nationally Determined Contributions (countries’ pledges to reduce their emissions of greenhouse gases made at the Paris meeting in December 2015 ) were to be fully implemented (an unlikely story), emissions of carbon dioxide will continue to rise—albeit more slowly—eventually settling out in 2100 at about the level they are now [2]. By this time, CO2 levels will be close to 600 ppm and global temperatures will have risen by about 3°C.

This is NOT a place where we want to be.

Clearly, the governments that signed up to the Paris Agreement have to do better.  But better at what?

Tucked away in the scenarios that show how the world can bring down levels of greenhouse gases are technologies called Negative Emission Technologies—or NETs. These are technologies that directly remove carbon dioxide out of the air.  Nature already provides us with two of them that work pretty well. These are the sinks that occur naturally in the environment: the terrestrial land sink and the oceans. Both operate at about 10 billion tonnes of CO2 a year—absorbing carbon dioxide from the atmosphere. [3]

But it’s not enough.

NET call

Are NETs an essential part of the drive to reduce emissions of carbon dioxide?

Chief among the NETs is BECCS: Bioenergy with carbon capture and storage.

This is a neat idea. Since trees and other plants absorb carbon dioxide when growing, why not cultivate fast-growing species of plants, burn them as fuel in power plants. Then all we have to do is remove the carbon dioxide from the exhaust gases and bury it underground.

Note that the concept relies on two separate processes.  First we have to produce biomass on a very large scale. This means using a lot of land that could otherwise be used for agriculture. Then the biomass has to be cut, harvested, transported, and processed into pellets before being conveyed to the power plants.  And then there’s the ash.  There is always ash with the combustion of solid fuels. And you will still get air pollution from the power plant.

Secondly, there’s the carbon capture bit—called Carbon Capture and Storage or CCS. Chemical engineers figured out how to do this a long time ago. It’s not difficult to absorb carbon dioxide from a gas stream.  The tricky part is putting it someplace else.

A 2018 report by the European Academies Science Advisory Council (EASAC) looked at the BECCS concept, together with five other negative emissions technologies:

  • Afforestation and reforestation
  • Land management to increase and fix soil organic carbon
  • Enhanced weathering
  • Direct air capture of CO2 with storage (DACCS), and
  • Ocean iron fertilisation

The report conclusions are not encouraging [4]:

Having reviewed the scientific evidence on several possible options for CO2 removal (CDR) using negative emissions technologies (NETs), we conclude that these technologies offer only limited realistic potential to remove carbon from the atmosphere and not on the scale envisaged in some climate scenarios (as much as several billion tonnes of carbon each year post-2050). Negative emission technologies may have a useful role to play but, on the basis of current information, not at the levels required to compensate for inadequate mitigation measures.

So BECCS doesn’t look like a good prospect. Nor do any of the others—including DACCS.

But if we separate the BE from the CCS, we might come to a different conclusion.

Carbon capture and storage technologies are under development in several countries. The Global CCS Institute, based in Australia, is understandably really upbeat about CCS. Their 2017 report on the status of CCS notes that 17 large-scale CCS facilities are operating worldwide, with four more coming onstream in 2018. These installations have the capacity to capture 37 million tonnes a year of CO2.  That may be small potatoes now—but the technology clearly has potential, and there’s a compelling argument to be made that governments should really look into providing funding to accelerate its development.

Assuming that carbon capture and storage develops into a viable and cost-effective tehnology capable of reducing CO2 emissions by several billion tonnes (Gt) a year, how should this technology be deployed?

No, we are going to add it on to fossil-fuel power plants. Fossil fuel powered electricity needs to be replaced by renewables. Period.

And the era of coal is over—it cannot be resuscitated by CCS technology. Nothing can clean up coal: not the mines, the tailings ponds, the ash pits, the coal trains, the mercury and the particulate air pollution—coal is a planetary health hazard.

But there is one place where carbon capture and storage might be really useful.

About a quarter of global CO2 emissions comes from industry—mostly from fossil fuels being used to generate steam and process heat—meaning very high temperatures.  Natural gas would generally be the most common fuel in this application.

It’s not evident that renewable energy can replace natural gas for process heat in large energy-intensive industries. Solar thermal can produce very high temperatures, but you need plenty of space to capture solar energy–which would then need to be conveyed to each point where high temperatures are needed. It would be bulky system: inflexible and probably quite difficult to control. Many industries are situated in peri-urban space where there is little or no possiblility of accessing the large areas of land needed to capture solar energy. The physical process of heat transfer itself is also a  problem.

So this is the sector where CCS should be deployed.

Meeting the Paris Agreement targets, even the lower one of 1.5 C, is definitely possible. But not in the way we are moving now. It will take a more vigorous commitment to replacing power plants with renewable energy technologies; stronger financial incentives to accelerate the adoption of electric vehicles (as California is now doing); and a sustained focus on improving energy efficiency—particularly in the built environment.

And in the hard-to-reach energy-intensive industrial sector, carbon capture and storage will ensure that CO2 emissions are kept to a minimum.



Diving deeper:

[1] See the Climate Action Tracker November 2017 update report at

[2] The CAT report shows the emissions trend line for current policies and NDC pledges as rising slowly from 2020 and then declining slightly back to approximately 2020 levels in 2100.

[3] See the Global Carbon Budget 2017 report at:

[4] Negative emission technologies: What role in meeting Paris Agreement targets? European Academies Science Advisory Council, EASAC policy report 35, February 2018.  See

see also : The dubious promise of bioenergy plus carbon capture, at


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