We Can't Cut Our Way to Net Zero

Even a perfectly decarbonized world has to pull carbon out of the air — and the sea.

Welcome to carbon removal’s blue frontier!

Part 1 of 7

 

For three decades, climate action has centered on a single imperative: stop emitting. Replace coal and gas with wind, solar, and nuclear. Electrify cars, heat, and industry. Wring waste out of the system. This shift from carbon-emitting to clean energy is the energy transition, and it is rightly the main event — the largest and most important lever we have.

But the transition has one feature that's easy to gloss over: it takes time. The world does not move from fossil fuels to clean energy overnight. It happens over decades, as non-emissive technologies mature, become cost-effective, and are adopted at scale. Throughout that long shift, we keep burning fossil fuels — adding still more carbon dioxide to an atmosphere already carrying a century and a half of past emissions.

That is the gap a second lever has to close. Alongside cutting emissions, we need to actively remove carbon dioxide from the air — both the vast stock already accumulated and the flow we can't yet stop emitting. That deliberate removal is Carbon Dioxide Removal, or CDR. Far from a fringe idea, it sits at the center of nearly every credible plan to hold warming near 1.5 °C. The two levers work together: the energy transition shrinks the flow of current and future emissions; CDR shrinks the accumulated stock from past and continuing hard-to-abate emissions.

What “net zero” really means

Here’s the part the phrase itself obscures. We are unlikely ever to reach a world that emits no carbon at all — some sources are simply too hard to abate: the chemistry of cement, the heat of steelmaking, the energy density demanded by aviation and shipping, and the methane from agriculture. “Net zero” doesn’t require zero emissions. It requires balance — a point at which the carbon we still add is matched, tonne for tonne, by the carbon we deliberately remove, so there is no net addition to the atmosphere. That is why pathways that hold warming to the Paris targets lean on CDR at enormous scale, and why the field has gone in a few short years from academic footnote to a market attracting serious capital.

So if we're going to remove billions of tonnes of carbon this century, the question becomes: from where?

Three arenas: land, air, and ocean

Carbon removal isn't one technology. It's a whole portfolio of them, and they sort naturally into three arenas depending on where they do their work.

Land is the oldest and, for now, the cheapest. Restore a forest, rebuild carbon in degraded soil, bury biomass as biochar — you’re enlisting photosynthesis, the removal engine nature already runs for free. The catch is that land is finite and the storage is reversible: a forest that burns hands its carbon straight back to the atmosphere.

Air is the frontier that grabs headlines. Direct Air Capture — DAC — uses banks of fans and chemical sorbents to strip CO₂ directly out of the passing breeze, then concentrate it and lock it underground. It's elegant, permanent, and can be located almost anywhere. It is also famously energy-hungry and expensive, with early costs running several hundred to over a thousand dollars per tonne. DAC is real, and improving fast — but it is working against the odds, because the atmosphere is a very dilute place to fish for carbon.

Ocean is the arena most people have never heard of — and the one with by far the most room to run.

The giant hiding in plain sight

Consider what the ocean has already done, entirely without our help. Of all the carbon dioxide humanity has emitted, the sea has quietly absorbed roughly 30%. Of all the excess heat our emissions have trapped, it has soaked up close to 90%. It holds something like 42 times as much carbon as the entire atmosphere holds. The ocean is not a bystander in the carbon cycle — it is the single largest carbon sink on the planet, and it has been dampening the blow of climate change for as long as we’ve been landing punches.

Now sit with the implication. The most powerful carbon-removal machine on Earth is already built, already running, and already operating at a scale no factory will ever match. Ocean-based Carbon Dioxide Removal — OCDR — is the science of safely nudging that machine to do a little more. Because it starts from such an enormous baseline, even a modest nudge could move the needle on net zero in a way land and air, on their own, cannot.

The lines between these arenas blur at the coastline, where mangroves, salt marshes, and seagrasses grow with one foot on land and one in the sea. By long-standing convention, that “blue carbon” is counted on the ocean’s side of the ledger — a useful reminder that these categories are a map, not the territory.

That “safely” is not a throwaway word. The ocean is a living system we depend on for food, weather, and half the oxygen we breathe, and every OCDR approach has to earn its license against real ecological questions. We’ll take those questions seriously throughout this series. But the prize is worth the scrutiny.

Where this series is going

Over the next six parts, I’ll map the entire OCDR landscape and the technologies racing to build it. The field divides cleanly into two categories:

●       Natural approaches, which harness the ocean's living engine — plants, algae, and photosynthesis — to pull down more carbon.

●       Technological approaches, which speed up and scale the ocean's own physics and chemistry — through mineral weathering, added alkalinity, and electrochemistry — to expand how much CO₂ seawater can hold.

We'll walk through each approach, weigh its real merits and risks, and meet the startups — spun out of Caltech, UCLA, Yale, and Stony Brook, alongside public-benefit corporations — betting that the answer to the carbon we can't stop emitting has been sitting under 70% of the planet's surface the whole time.

The energy transition will do the heavy lifting. But it cannot do all of it, or do it fast enough on its own — which is why removal has moved from optional to essential. And of all the places to pull carbon back out, the largest and least explored has been beneath us all along. That’s where we go next.

 

Next in the series — Part 2: The Ocean, CDR’s Sleeping Giant. Why the sea is the most underexplored arena in carbon removal, and how to read the two-family map of everything that follows.