We’re Doing Net Zero All Wrong, Scientists Say
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Ever since the historic Paris Climate Accords in 2015, the phrase “net zero” has been on the lips of every corporation, industry lobbyist, and politician, all promising they are working hard to do their part to avoid turning the planet we live on into a burnt cinder. But what does the phrase even mean?
Bloomberg reported this week that while officials from 197 countries agreed earlier this month to new rules governing how they can buy and sell credits to neutralize carbon emissions, some of the biggest names in climate science — the very people who defined “net zero” in 2009 — found something wrong with the math underlying those debates. “Achieving ‘net zero’ no longer means what we meant by it,” said Myles Allen, professor of geosystem science at University of Oxford, who was one of the authors of a new paper published last month in the journal Nature.
A Vast Oversimplification
Their analysis skewers an assumption at the heart of how countries and companies track emissions — that a ton of CO2 is the same everywhere whether it’s dispersed in the atmosphere, embedded in forest wood, or pulled from the air and pumped deep underground forever. That fungibility is the foundation of carbon markets. It lets a ton of CO2 in a forest stand as a fair trade for a ton put in the atmosphere.
That rule of thumb turns out to be a vast oversimplification that could render many well-meaning net zero efforts meaningless. The confusion stems from a basic fact about how the Earth’s carbon cycle works. Scientists know that less than half of the emissions human activity pumps into the atmosphere stays in the atmosphere. The rest gets absorbed into the land and oceans. To keep track of all that carbon — and how they assign responsibility for removing it, scientists keep two ledgers — one for nature and one for humanity. All the CO2 absorbed every year into land, trees, and water is a service the planet offers to wash humanity’s past CO2 emissions out of the air. So, these carbon drawdowns go into the nature ledger.
It’s important to emphasize that the land and the oceans are drawing down emissions associated with past activity, which means they cannot be relied on to also neutralize future emissions. This is where the revelation comes in — countries may have been double counting. In other words, it’s redundant for countries to claim credit for CO2 reductions already being done by land and oceans. Those emissions are already spoken for. “We can’t count on them [emissions] to do two jobs at once. That’s the point,” Allen said. “If we’re going to count on them to mop up our historical emissions… we can’t at the same time use them to offset future fossil fuel emissions.”
A Hidden 0.5ºC
These differences between natural and industrial bookkeeping add up. For example, Allen said, consider a situation in which, using current carbon accounting, the world was expected to stay below 1.5ºC. The flaws in accounting are so significant that they could conceal another 0.5ºC rise. There are consequences for this accounting mismatch. The first is, it increases the urgency to stop burning fossil fuels, the authors write, or to capture and bury pollution with emerging methods. The climate that humanity grew up in relied on millions of years of coal, oil and gas sitting underground. The main solution therefore is to leave it there, capture the carbon from smokestacks and permanently bury it, or clean it out of the open air. (Emphasis added.) Returning carbon underground is “geological net zero,” and it’s what the authors originally had in mind in 2009, yet no countries are currently pursuing it.
Separate from fossil fuel burning and carbon capturing, they write, nature must be left alone to passively soak up history’s CO2. And all that land needs to be conserved, undeveloped, to keep the carbon out of the atmosphere and pull down even more. Rich countries bear historic responsibility for ensuring that happens, they argue in their latest research paper.
The Managed Land Fallacy
As if this weren’t complicated enough, there is more to the story than two ledgers, with past carbon falling into nature and future carbon captured and stashed underground. That’s because there is value to human management of land that reduces atmospheric CO2. In other words, if “managed land” is proven to take down CO2 then those tons can be counted against emissions, the scientists say. But what “managed land” means is difficult to pin down. Countries have no uniform standard and often claim all of their land as managed. In fact, so much land is claimed that their combined pledges are virtually impossible to foresee happening. They may be taking credit for emissions already in nature’s ledger.
There are other reasons why storing carbon in the biosphere is inferior to geological storage, the authors write. As wildfires demonstrate every year, there is nothing permanent about living things. In 2023, the hottest year on record, trees and land absorbed virtually no carbon. Any potential slowdown in the land and ocean acting as carbon sponges leaves a greater amount in the atmosphere, which aggravates global warming even further.
Apples To Apples
The paper pulls together into one place a number of concerns scientists have accumulated about land use and carbon accounting, said Pamela McElwee, a Rutgers University professor and contributor to the UN Intergovernmental Panel on Climate Change. That includes separating how everyone accounts for natural and industrial CO2 drawdown. Countries should be able deduct CO2 that’s drawn down permanently and sequestered back into the Earth from their gross fossil fuel emissions. But carbon absorbed by land and oceans doesn’t count as “geological net zero,” and should not be credited against emissions.
“It really needs to be apples to apples and so let’s treat it that way,” McElwee said. She admits it is difficult to suggest any reforms that might take already limited funding away from forest management. “If I could be assured that we could do both those things simultaneously” — reach geological net zero and preserve natural drawdown — “that would be ideal.”
A study by Cyril Brunner, Zeke Hausfather, and Reto Knutti published in the journal Communications Earth & Environment on November 11, 2024, comes to a startling conclusion. “Our findings suggest that a CO2 storage period of less than 1000 years (emphasis added) is insufficient for neutralizing remaining fossil CO2 emissions under net zero emissions.” Reto Knutti is also an author of the Nature study that is today’s topic. Those findings put even more pressure on defining net zero correctly. If present calculations are based on carbon storage that only lasts a century or two, they are fatally flawed and should be ignored.
The Takeaway
People who live in the internet age may not be familiar with Mark Twain. Many who are familiar think that he was just a humorist like Dave Barry, but he was much more than that. He was a chronicler of American culture at a time when such things were rare. He also had a way of dispensing wisdom in a way that did not sound preachy. “It ain’t what you don’t know that gets you into trouble. It’s what you know for sure that just ain’t so,” was one of his more famous lines. He also observed, “Man is the only animal that blushes — or needs to.”
What this latest study reveals is that governments and industry have taken the original concept of net zero and redefined it to the point where is it meaningless. That is not a harmless error. It means much of the discussion about the measures being taken to address global heating is false and that fallacy is leading us astray — dangerously so. The scientists have sounded the alarm — we are adding 2 plus 2 and getting eleventy-seven. In other words, we are flying blind into the future while holding the map upside down. This is not likely to end well.
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