Slog Bog

ADD-ON SECTION: Are temperature reductions additive? And what if OTEC makes H₂ / NH₃ for “most transportation”?

Sound-bite bullets (tight)

• []Additive “cooling wedges”: roughly OK as a first-pass budgeting tool, but not guaranteed—feedbacks, circulation, and thresholds make full additivity break at scale.
  []Fossil “heat” vs fossil “CO₂”: direct waste heat is a second-order effect; the long-lived warming punch is from greenhouse forcing.
  []OTEC “net-cooling”: not heat deletion—it’s surface→depth heat redistribution while operating, plus avoided emissions if it displaces combustion.
  []Nickoloff calibration point (2100): in OTEC10, global SAT is 1.5°C lower than OTEC0; ~60% mixing and ~40% emissions in 2100. OTEC15 reaches up to ~2.5°C by 2100 vs OTEC0.

Keep these URLs verbatim:
https://link.springer.com/article/10.10 ... 25-03933-4
https://link.springer.com/article/10.10 ... 25-03944-1

[hr]

1) Are temperature reductions additive?

• []Short answer: approximately for small perturbations; not strictly as you scale up.
  []Why it fails: OTEC changes ocean stratification/mixing and regional SST patterns; those can change cloud/ice feedbacks and the “pattern” of warming. So “ΔT from lever A + ΔT from lever B” is a decent scoping heuristic, but not a law of nature.
• Practical use: treat additivity as a planning approximation, then expect interaction terms (±) at multi-TW deployments.

[hr]

2) “Exchanging net-heat of fossil/nuclear” with “net-cooling of OTEC” (what actually matters)

• []Fossil/nuclear waste heat: yes, it’s heat—but globally it’s small compared to the radiative forcing from CO₂ when you burn fossil fuels.
  []OTEC isn’t a heat sink: it moves heat (warm surface → cold/deeper discharge) and can reduce surface warming while operating.
  []The dominant climate swap is: fossil CO₂ forcing → avoided forcing when OTEC displaces combustion.
  []OTEC’s “extra knob” (vs wind/solar): the Nickoloff work explicitly shows a sizable mixing-driven cooling component while OTEC is running (about 60% of the 2100 cooling signal in OTEC10).

[hr]

3) If OTEC is pushed to make H₂ / NH₃ for most transportation — what happens to total temperature reduction?

3A) Emissions wedge you’d be attacking

• Transport CO₂ is huge: IEA puts 2022 transport-sector CO₂ at nearly 8 Gt CO₂. That’s the order-of-magnitude ceiling for “avoid CO₂ by decarbonizing most transport.”
  Source (keep URL): https://www.iea.org/energy-system/transport

3B) Electricity penalty: H₂/NH₃ as a transport energy carrier is conversion-heavy

• []Hydrogen electrolysis electricity: typically 50–55 kWh per kg H₂.
  Sources (keep URLs):
  https://world-nuclear.org/information-l ... n-and-uses
  https://www.power-h2.com/insights/hydrogen-electrolysis
  []Green ammonia electricity (rule-of-thumb): one published protocol example totals about ~10.3 kWh per kg NH₃ (electrolysis + N₂ + Haber–Bosch electric loads in that accounting).
  Source (keep URL): https://gh2.org/publication/invitation- ... a-protocol

Implication: if you use OTEC electricity to make H₂/NH₃ and then burn/use it in engines/turbines or run fuel cells, you usually need more primary electricity than direct electrification. So “OTEC TW needed” to power “most transport” depends heavily on:

• []how much transport is directly electrified (best case),
  []how much is fuel-cell H₂ (middle),
• how much is NH₃-to-power (often lower round-trip efficiency, but easier storage/shipping).

3C) How to fold this into the earlier OTEC °C calibration

• []The Nickoloff implied ΔT2100 scale already bundles two mechanisms:
  • []mixing/redistribution cooling while operating, and
    []emissions reduction cooling from displaced fossil energy in their scenarios.
  []So, if OTEC also decarbonizes transport via H₂/NH₃, you’re adding an extra emissions wedge (potentially up to that “~8 Gt/yr” transport scale), which should increase the emissions-driven fraction of the cooling—but it won’t be perfectly additive with the power-sector wedge because of system interactions.

3D) A tight, scoping-style estimate (consistent with our earlier heuristic)

• []Earlier heuristic from Nickoloff anchors:
  ΔT2100 ≈ (0.150 to 0.167) × TW (vs their OTEC0 control)
  []Transport fuels don’t automatically change the mixing term (that’s driven by the TW of OTEC moving seawater heat).
• Transport fuels DO increase the emissions term (more fossil displaced), but only if the displaced transport is actually fossil and the H₂/NH₃ supply chain is truly low-carbon.

Practical “plug-in” rule for your scenario post:

• []Treat the implied ΔT2100 range from TW of OTEC as your mixing + baseline electricity-displacement package (as already posted).
  []Then add a separate line item: “extra avoided CO₂ from transport” up to ~8 Gt/yr (if you truly decarbonize most transport), and note: this pushes the emissions-driven share above the ~40% value quoted for OTEC10 (but do not claim strict additivity).

If you want, I can produce a one-paragraph “transport addendum” that matches your earlier tables exactly (same TW/η grid), with two extra columns:

• []“Transport CO₂ avoided (Gt/yr) — assumed fraction of ~8 Gt/yr”
  []“Net implied ΔT2100 — baseline (from TW) + emissions wedge note (non-additive)”

night0WL wrote: Wed Feb 18, 2026 5:22 am

AIEA

Summarize delta T maximizing OTEC/hydrogen use
versus the path we actually took abandoning the Carter Doctrine. ++

Delta-T summary (max OTEC + H₂/NH₃ push vs the path we actually took)

1) The cleanest published “max-OTEC” calibration
Nickoloff et al. ran coupled-climate experiments with large OTEC rollouts (OTEC3/5/7/10/15 TW). Their key global-mean surface air temperature (SAT) results vs a high-emissions control (OTEC0):

• []OTEC10: −1.5°C in year 2100 relative to OTEC0. In 2100, ~60% of that cooling is from OTEC-induced mixing/redistribution and ~40% from OTEC-related emissions reductions. 
  []OTEC15: global SAT decreases of up to −2.5°C by 2100 relative to OTEC0 (reported as “up to” in the same research line). 

Keep these URLs verbatim:
https://link.springer.com/article/10.10 ... 25-03933-4
https://link.springer.com/article/10.10 ... 25-03944-1

Interpretation as “delta-T vs the path we took”:
If “the path we took” is effectively “OTEC0 (no material deployment),” then the model-implied difference by 2100 is roughly:

• []~1.5°C cooler (if we had driven to ~10 TW scale), and
  []up to ~2.5°C cooler (if we had driven to ~15 TW scale).

[hr]

2) What changes when you add “OTEC → H₂ / NH₃ → most transportation”
This matters primarily through the emissions-reduction channel (the “~40%” piece in OTEC10), not through the mixing channel (which is set mainly by TW of OTEC moving seawater heat).

A hard reality check on the size of the transport wedge:

• IEA: In 2022, global CO₂ emissions from transport were nearly 8 Gt CO₂. 
  Keep URL verbatim: https://www.iea.org/energy-system/transport

So, if OTEC-derived H₂/NH₃ displaced “most” fossil transport, you’d be attacking an additional wedge on the order of multiple GtCO₂/yr. That would tend to make the emissions-driven portion of the cooling larger than the ~40% share quoted for OTEC10—because you’d be displacing fossil beyond just the power sector.

But: you can’t just add “more avoided CO₂” and claim a clean extra °C without running the coupled model with that explicit extra displacement, because:

• []the climate response is not perfectly additive at multi-TW scale (feedbacks + circulation + pattern effects), and
  []the H₂/NH₃ pathway is electricity-hungry (conversion losses), so it changes how much OTEC TW you actually need for “most transportation.”

Best defensible bottom line (without over-claiming):

• []Baseline max-OTEC signal: ~−1.5°C (10 TW) to up to ~−2.5°C (15 TW) by 2100 vs “no OTEC industry.” 
  []Adding OTEC→H₂/NH₃ for transport likely pushes you toward the high end of that cooling range faster (bigger emissions wedge), because transport is ~8 GtCO₂/yr scale today. 
• Claiming “beyond −2.5°C” is not defensible from these papers alone; that requires a new scenario run that explicitly includes the extra transport displacement and the extra OTEC capacity required to supply it.

night0WL wrote: Wed Feb 18, 2026 5:33 am

AIEA

2^o C is 3.6^o F so was mostly a viable solution.

Yes on the conversion: 2^oC = 3.6^oF.

But the key point is what “2^oC” actually represents. The 2°C threshold is a global mean target relative to a preindustrial baseline—not a uniform “only 3.6°F everywhere” change. Local/regional changes (land vs ocean, Arctic amplification, extremes) can be much larger than the global mean.

So was it “mostly a viable solution”? If you mean “could Carter-style OTEC leadership have materially altered the climate trajectory,” the best defensible reading is:

• []At multi-TW scale, the published OTEC modeling indicates order-1–2°C of global mean cooling by 2100 relative to a high-emissions control (e.g., ~−1.5°C at 10 TW; up to ~−2.5°C at 15 TW). That’s not trivial—those are “big wedge” magnitudes.
  []That level of impact is only plausible with an actual industry ramp (pipes, platforms, fleets, tropical deployment), plus the emissions displacement that comes with it (and potentially more if OTEC drives H₂/NH₃ into transport).
• But “2°C” isn’t the whole story: even if you hold the global mean down, you still fight regional damages and extremes; and if you miss it, the damage function isn’t linear.

Bottom line: “Only 3.6°F” sounds small, but on a planet-scale mean it’s enormous—and large-scale OTEC (if actually executed) looks like one of the few single levers that can plausibly move the needle by ~1–2°C in the Nickoloff-style scenarios. — emphasis Night0WL