"Clean" is a meaningless word, like processed food saying it's "natural". Or like Obama calling for "clean coal".

I drilled through the links to https://www.energy.gov/articles/cop28-countries-launch-declaration-intent-clean-hydrogen for a definition.
"The United States, which uses the term “clean hydrogen” rather than “low-carbon hydrogen” nationally, understands “low-carbon” in this document and others as inclusive of hydrogen produced with renewable energy, nuclear energy, or carbon capture and storage, and therefore not inclusive of hydrogen produced with unabated fossil energy, including natural gas. "

They're greenwashing black H. They'll use this vague and confusing terminology to hide the fact that the H will be produced from fracked gas or petroleum, which will release as much carbon into the atmosphere as burning the gas or oil, and use this as an excuse to keep drilling and building pipelines.

I'm a big proponent of hydrogen. It's an amazingly common and abundant element which can be derived from water, not some extractive mineral under the control of international cartels. The oil barons see this as a threat, and they're trying to steer the hydrogen industry towards their extractive and monopolistic models. It looks like they've already captured energy.gov, as they have COP.

I think we could transition to green hydrogen through a period using black hydrogen from fossil sources until we achieve economy of scale in produsing green hydrogen, but the oil barons won't relinquish hold on the energy economy voluntarily. They'll do everything they can to sabotage green hydrogen. "Look, the economics say that we need to produce it from fossil sources", while ignoring the external costs of their fossil pollution. We'll be emitting as much carbon by using black hydrogen greenwashed as "clean" hydrogen.

The use of the word "clean" in this context is a red herring.

The carbon dioxide produced is easily captured. In the NOVA documentary, they show plants made during the space race, in which the CO₂ is flowing out in a labeled pipe “to be used to make fizzy drinks.”

Having pure CO₂ like this, it can be (relatively) easily “sequestered.”

but I think it's a red herring. It's untested and problem-plagued.

Using the "fizzy drinks" example, that carbon still enters the atmosphere through bubbles and belches.

The petrobarons say that they will store the CO2 underground. What they are really doing is using the compressed CO2 in oil fields to force out more oil from the wells.

The fizzy drinks are carbonic acid. Storing CO2 underground means that we will create large pools of mild acid in deep rock formations. We have NO idea of the geological effects of this, but we can get a hint from the highly eroded and hollowed-out formations in karst terrain, where the limestone has been dissolved by carbonic acid formed by rain reacting with CO2.

from a wiki: "This produces carbonic acid (H2CO3) which dissociates into a bicarbonate ion (HCO3-) and a hydrogen ion (H+). " https://en.wikipedia.org/wiki/Ocean_acidification
The hydrogen ion is the acid.

I would favor carbon capture a bit more if the CO2 can be used to immediately make some form of stable, non-toxic solid material like bricks or concrete. But most petro-products are used to make highly toxic materials, like the vinyl chloride of East Palestine fame or the building materials that poisoned groundwater and wells in Maui when they burned.

The only carbon capture I trust is the photosynthesis that created the fossil fuels in the first place. If the words come from petrobarons, we can trust that they are self-serving lies.

There have been efforts to make accelerated artificial photosynthesis, with non-toxic carbon byproducts (possibly even edibles), but I haven't heard any more about this in years.

That said, several years ago I suggested using the economy of scale of abundant black H to build out a hydrogen infrastructure of delivery and storage systems, then switch to green H for supply. The problem with this is that the petrobarons will then say that it's uneconomical to switch to green H, or use some other excuse to keep their stranglehold on the world.

The “Keeling Curve” has a sawtooth, because a portion of the carbon dioxide captured during the warm months in the Northern Hemisphere is released in the cold months.

This past year, tremendous amounts of photosynthetically sequestered carbon is being released into the atmosphere.
https://firms.modaps.eosdis.nasa.gov/usfs/map/


Geologically sequestered carbon is quite stable: