Net-Zero may not be enough: Time to go Carbon Negative?

By Robert Speht, specialist in renewable energy

The Background

It turns out that Net-Zero will not solve our man made Climate Emergency..... at least not with the definition that everyone is currently using. Firstly let’s define what we mean by Net-Zero. 

Generally this is taken to mean that Globally, Nationally, at a corporate level or at an individual level the energy that we use is produced with zero Carbon Dioxide (CO2) being emitted on balance. Various entities (countries, companies etc) now have targets to reach Net-Zero CO2 emissions for their energy use by a specific date. For some this is the year 2030, others have 2040, 2050 etc.

Of course, it is laudable to try and reach a net “zero” CO2 output in an instantaneous measure. Some will argue that this means emitting CO2 and also having measures to reduce CO2 and that the net of the two are zero, and that this is somehow not good enough. I’m no purist, and don’t subscribe to this ideal. I think a “net” Zero is good enough. 

However getting from where we are today to a position of Net-Zero, does not take in to account the CO2 we have emitted over the last 200 years. It’s the difference between “instantaneous net zero” and “total net zero” or maybe “real net zero”. 

Or as Microsoft called it in a recent announcement “carbon negative”. In their case they have calculated backwards how much CO2 they have emitted in all their operations since 1973 and aim to “go negative” to this amount, and then be Net-Zero going forwards.

That is however, just one company. What about all of humankind and everything we have done since industrialisation started? We would need to calculate how much CO2 we will have emitted in total (over say 200 years) as a species by the time we are predicted to be at Net-Zero. Then we need to work our how much of that CO2 we need to “pay back” and then work out how we will pay it back, and who will pay it back.

In general then, at a global level we need to be aiming for CO2-Negative not Net-Zero CO2. A number of companies in recent weeks have announced strategies to become Carbon Negative but to date I have not heard of any government talking about it for a nation and no one seems to be discussing it at a global level. Indeed our leaders seem to be struggling to get to Net-Zero.

The back-of-the-envelope calculation

I wanted to get a sense of how big the task would be to reach a Total Net-Zero globally, and here is my first stab at quantifying it. Not a scientific model, but playing around with some numbers to give us a ball-park.

Since the start of the Industrial Revolution, more than 2,000 billion metric tonnes of carbon dioxide have been added to the atmosphere by human activities according to the Global Carbon Project. Annual CO2 emissions have have risen to more than 36 billion metric tonnes per year, based on data from the Carbon Dioxide Information Analysis Center (CDIAC).

If we say that we will hit Net-Zero CO2 globally at some point in the next 15-25 years and that we peak at 40 billion tonnes per year emissions (slightly up from the current 36 billion) then we decrease from 40 billion down to zero over something like 12-22 years we see an additional emission of 354-554 billion tonnes on top of the 2,000 billion tonnes. 

This gives 2354-2554 billion tonnes CO2 that will have been emitted by the time humans get to Net-Zero. And we would achieve this by the year 2035-45.

If we want to repair the damage we should re-sequester (lock it back away from the atmosphere) the CO2 and eventually get back to Total Net-Zero.

Let’s take the midpoint of 2554 GtCO2, and if we want to repair half the damage and re-sequester half the CO2 that would be 1277 GtCO2

And if we want to re-sequester over 50 years that would be minus 25.5 GtCO2 emissions on average for 50 years from the point we hit Net-Zero in 2035-2045 taking us to 2085-95.

Of course in the first of those 50 years it will be very small and will build up over time. A straight line growth would have almost zero in year one and minus 51 GtCO2/year in year 50 with the midpoint of minus 25.5 GtCO2/year in year 2060-70. 

If we want to undo all the CO2 emitted by humans, we would need to either double the rate, or double the re-sequester period, or maybe somewhere in the middle of the two positions. So somewhere between 50 and 100 years, maybe 75 years of re-sequestration and a rate of re-sequestration starting at zero in the year we hit Net-Zero and ending at 68 GtCO2/year in the year 2085-2095.

To put this is human terms, it means we continue to emit CO2, hopefully in ever lower amounts, for the next 0.5-0.8 generations (15-25 years), where a human generation is considered to be 30 years. Then if we wanted to undo the damage done cumulatively up to that point we will need to re-sequester CO2 for a further 1.6 and 3.3 human generations. The total then being 2.1-4.1 human generations. 

For someone who today is 25 years old, they will be 40-50 years old by the time we hit Net-Zero instantaneous emissions, they would be 64-99 years old by time we had re-sequestered half the cumulative CO2 emitted by humans and somewhere between 88 and 148 years old before we have reached “Total Net-Zero”. 

Even over this extended length of time it is going to take an unprecedented amount of effort by national governments, and supranational organisations to get there. What I outline here in my back-of-the-envelope is the most optimistic scenario I can conceive of. I expect to be somewhat disappointed by our leaders over the coming years and decades, and I suspect it will take much longer.

What do we mean by “re-sequestration”?

Ecowatch lists several main ways to re-sequester CO2, and I have summarised them here;

Trees - (Concerted efforts to plant trees in new places (afforest) and replant deforested acreage (reforest) could increase this by a gigaton or more, depending on species, growth patterns, economics, politics and other variables.)

Carbon Farming - Most farming is intended to produce something that's harvested from the land. Carbon farming is the opposite. It uses plants to trap CO2, then strategically uses practices such as reducing tilling, planting longer-rooted crops and incorporating organic materials into the soil to encourage the trapped carbon to move into—and stay in—the soil.

Fertilising the Ocean - Plants and plantlike organisms that live in the ocean absorb immeasurable amounts of CO2 each year, their ability to do so limited only by the availability of iron, nitrogen and other nutrients they need to grow and multiply. So researchers are looking at strategies for fertilizing the ocean or bringing nutrients up from the depths to hyperdrive plants' ability to trap and store carbon.

Direct Air Capture and Storage - The carbon-sequestering containers from Arizona State University's Lackner, along with other projects such as Climeworks' just-opened carbon-trapping facility in Switzerland, represent one of the more widely discussed greenhouse gas capture and storage technologies being proposed today. Known as direct air capture and storage, this approach uses chemicals or solids to capture the gas from thin air, then, as in the case of BECCS, stores it for the long haul underground or in long-lasting materials.

Rock Solutions - CO2 is naturally removed from the atmosphere every day through reactions between rainwater and rocks. Some climate scientists propose enhancing this process—and so increasing CO2 removal from the atmosphere—through artificial measures such as crushing rocks and exposing them to CO2 in a reaction chamber or spreading them over large areas of land or ocean, increasing the surface area over which the reactions can occur.

As currently imagined, strategies to enhance carbon storage by reacting CO2 with rocks are expensive and energy-intensive due to the need to transport and process large quantities of heavy material. Some also require extensive land use and so have potential to compete with other needs such as food production and biodiversity protection. Researchers are looking at ways to use mine waste and otherwise refine the strategy to reduce costs and increase efficiency.

The Conclusions

We will, globally at least, undershoot our UN-agreed CO2 targets, and will need at some point in time to go Carbon Negative, if only to bring us back to what we have agreed to, and to what we would like to achieve.

Once we have got to the point where we are Carbon Negative and have finally, after some time, achieved our CO2 goals, to then start producing more CO2, to then reverse the advances in energy production, efficiency and usage would be illogical.

So logically we can do better than aiming for global temperature rises of 1.5C, and the “do nothing” option in approximately 2035-45 will in fact be a Carbon Negative economy where without changing anything we will gradually undo the CO2 damage of the last 200 years.

Around 70 years from now (plus or minus 10 years) we will need to make a decision, globally, as to whether we want to allow CO2 to reduce below those of pre-industrial levels. My gut feeling is that our planet can take a little cooling, but we should by that time have worked out a way to keep it carefully in balance.

Of the many re-sequestration methods, I personally prefer the re-forestation option, and look forward to a time where we see much more new woodland. To my mind this seems like the most natural solution. We see countries pledging tree planting in the hundreds of millions per year, but added together globally this is hundreds of billions of additional trees - every year, for many decades, possibility indefinitely. We recently saw in Davos that the World Economic Forum announced a global initiative to plant one trillion trees. 

Finally, I would like to hear our leaders talk about Carbon Negative or Total Net-Zero. It’s time to move the goalposts.

Notes to editors

Robert Speht is a specialist in renewable energy projects and has been involved over 20 years in the industry with a combined total of over 13 GW of installed capacity and an investment value of more than US$ 23 billion. That's enough renewable energy to power more than 10 million UK homes. More at www.dhirubhai.net/in/robspeht 

For more information on what it means to be Net Zero - London School of Economics; What is net zero?

https://www.lse.ac.uk/GranthamInstitute/news/what-is-net-zero/

More information on the Global Carbon Project ate;

https://en.m.wikipedia.org/wiki/Global_Carbon_Project and at https://www.globalcarbonproject.org/about/index.htm

More information about the the Carbon Dioxide Information Analysis Center (CDIAC) at;

https://cdiac.ess-dive.lbl.gov 

Analysis: How much ‘carbon budget’ is left to limit global warming to 1.5C?

https://www.carbonbrief.org/analysis-how-much-carbon-budget-is-left-to-limit-global-warming-to-1-5c/amp

For more information on Carbon sequestration;

https://en.m.wikipedia.org/wiki/Carbon_sequestration

For more information on Carbon Sequestration - 8 Ways to Sequester Carbon to Avoid Climate Catastrophe

https://www.ecowatch.com/amp/carbon-sequestration-2461971411

Microsoft makes 'carbon negative' pledge

https://www.bbc.co.uk/news/technology-51133811

AstraZeneca commits to being carbon negative by 2030

https://pharmaphorum.com/news/astrazeneca-commits-to-being-carbon-negative-by-2030/

Drax sets world-first ambition to become carbon negative by 2030

https://www.powerengineeringint.com/2019/12/10/drax-sets-world-first-ambition-to-become-carbon-negative-by-2030/

Restoring the Earth: 1t.org Announced to Accelerate Nature Restoration to Tackle Climate and Biodiversity Crises

https://www.weforum.org/press/2020/01/restoring-the-earth-1t-org-announced-to-accelerate-nature-restoration-to-tackle-climate-and-biodiversity-crises/