The third number is now showing up in our blood

For a hundred years and more we have run the world on two numbers. What a thing costs to build, and what it costs to run. Capital cost and operating cost. Those two numbers get scrutinized line by line, defended in front of boards, and optimized to the fourth decimal place. And the whole time, a third number has been accruing in the background, in the carbon and water and nitrogen cycles, on a ledger nobody was required to total. My forthcoming book, The Third Number, is about that account: the physical consequences of what we build, settling over generational time, posting either as credits or as liabilities. The animating question of the book is written in the language of the people who sign the checks. What gets counted on nature's ledger, and over generational time, do your third numbers post as credits or liabilities?

For most of my career that third number was invisible until it landed, usually decades later, on someone else's desk. Think PFAS, leaded gasoline, DDT, CFCs, and so on. This month, a new third number got a little harder to ignore because it turned up somewhere new: in human blood.

A liability, detected in the bloodstream

In February 2026, Alexander Larcombe and Phil Bierwirth published a paper in Air Quality, Atmosphere and Health with a title that reads less like a study and more like a warning: "Carbon dioxide overload, detected in human blood, suggests a potentially toxic atmosphere within 50 years." They used data from the U.S. National Health and Nutrition Examination Survey, including blood chemistry from 33,546 adults sampled over two decades, and used serum bicarbonate, calcium, and phosphorus as indirect proxies for what rising atmospheric carbon dioxide is doing inside the body.

Our blood is tracking the air
Serum bicarbonate has risen ~7% since 1999, in lockstep with CO₂, on course to cross the upper healthy limit around 2076.

The trend they found is not subtle. Average blood bicarbonate rose about seven percent between 1999 and 2020, reaching 25.3 milliequivalents per litre, tracking the rise in atmospheric carbon dioxide over the same years almost line for line. Calcium and phosphorus fell over the same window. Project the bicarbonate trend forward at its measured rate and it reaches the top of the accepted healthy range in about half a century. Calcium and phosphorus reach the limits of theirs by the end of this century.

As carbon rises, minerals fall
Calcium and phosphorus have declined steadily as the body buffers CO₂, trending toward deficiency thresholds by 2099 and 2085.

The authors are careful, and their care is the point. These are proxies, not a diagnosis, and a projection is not a prophecy. But the direction is measured, not modeled. Atmospheric carbon dioxide has climbed from under 340 parts per million in 1980 to over 420 today, and it is still rising by more than two parts per million every year, against a pre-industrial baseline near 280. The paper's conclusion is a single, unglamorous sentence: there is an urgent need for significant reductions in anthropogenic carbon dioxide emissions to safeguard public health.

Spend time digesting the study, and you begin to see what that study actually is. It is the third number, made visible in the one ledger no executive can externalize onto a successor: their own body, and their children's. The liability did not appear this year. It has been accruing the entire time, in increments too small to trigger any of the alarms we've built. Gradually, and then, on a fifty-year clock, suddenly. That is exactly how every deferred liability I have ever watched that lands on a balance sheet behaves, and it is why the discipline of counting the third number before the concrete is poured is not a moral posture. It is arithmetic, and the arithmetic is no longer abstract.

The third number starts before the limit
The liability compounds long before any blood value crosses a clinical line, gradually, then suddenly.

The other half of the ledger

Here is the part most climate coverage misses, and the part that should interest anyone building or funding the future. A ledger with only debits on it is an indictment, and nobody builds an industry on an indictment. The same account that is filled with this liability can be deliberately filled with credits. Nature has been running a balanced carbon cycle for nearly four billion years, not because it is perfect, but because the biological designs that did not complete the loop did not survive to be copied. That long, tested library is now readable, and a set of solutions is being drawn from it that treat carbon not as waste to be buried at cost, but as a feedstock to be used.

Artificial photosynthesis that turns carbon dioxide and sunlight into fuel and material. Building materials that mineralize carbon into the structure itself, so a wall becomes a place carbon goes to stay rather than a place it comes from. Infrastructure designed to absorb across its whole standing life instead of only emitting during its construction. These are the solution sets being developed right now, and they are the credit entries the third number is waiting for. The question is not whether they work in a laboratory. Many of them do. The question is whether they can be scaled before the liability crystallizes, and scaling is a different problem from inventing.

Why scale is the real problem, and who solves it

A breakthrough dies in the lab for want of the unglamorous things: a supply chain, a standard, capital that can price the risk, a manufacturing partner, a regulator who understands what is being proposed. Semiconductors learned this the hard way in the 1980s and solved it not with a better transistor but with a shared way of counting, a cost-of-ownership metric, and a standard (SEMI E-35) that let rivals who did not trust each other at all agree on the number before they competed on everything else.

Biomimetics International exists to serve as a mediating and enabling table for this industry. It is a young network of networks, and its power is not in building the machines. It is in convening the people who can scale them: the researchers, the venture capital, the corporate sustainability officers, and the policymakers who normally work in separate silos, brought into the same room to create the intellectual collisions that turn a lab result into a commercial venture. It opens the door to three factors that determine whether a carbon-reducing idea reaches the world or dies quietly.

It de-risks. By defining a standardized recognition index for what a genuinely regenerative, carbon-positive project looks like on evidence, it gives a lender something to underwrite and a construction firm the confidence to invest in carbon-sequestering material instead of guessing. This is the discipline at the center of the book: recognition precedes valuation. You cannot price what you have not first agreed to recognize, measure, and value, and the industry cannot finance carbon solutions; it currently has no shared way to measure.

It translates. Biological wisdom becomes industrial strategy only when someone reframes carbon capture from an expensive add-on into the core of a business model. A building that pays for itself by standing there absorbing CO2 is a different proposition to a board than a compliance cost for not doing more, and the reframing is what unlocks the balance sheet.

And it makes the work visible. When a promising technology is amplified by a credible convener, it earns the recognition that moves it from a niche project to a mainstream solution, and it creates the market demand that pulls the next round of investment in behind it.

The urgency is now measurable

The reason to act is no longer only the polar bear or the coastline. It is a trend line in our blood panels, moving toward the edge of the healthy range on a schedule a person alive today can expect to see. The liability side of the ledger just got a start date and a point of no return, your expiration date. On the credit side, the nature-inspired solutions that can draw carbon back down and lock it away exist, and they are waiting for the scaffolding that lets capital recognize and scale them.

That scaffolding is being built now, in public, and there is a table where it happens. Biomimetics International convenes it, and the annual working session, Biomimetics26, is where the standard and the solutions meet the people who can fund and deploy them. The Third Number is one door into that room, and this is the argument it exists to make, stated as plainly as a blood test: the account is running whether or not we write it down. Nature is the ultimate arbiter, it doesn't care what you think or believe, but it does keep a ledger and issues rejection notices. We just got ours. The only question left is whether our entries post as credits, or as liabilities.

The clock is now measured in one lifetime years.

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