CO2 Pathways

So realistic best-case:

Emissions fall meaningfully, but not fast enough to prevent overshoot.

How quickly can CO2 emissions be realistically mitigated?

From ChagGPT 10 January 10, 2026

The fastest realistic global decarbonization rate is about 3–6% per year.
Sustained rates above ~7–8% are historically near-impossible.

That comes from energy system inertia, not politics.

1️⃣ What history says is actually possible

When countries decarbonize fast, it almost always happens during economic collapse or forced energy substitution, not smooth transitions.

Here are the fastest sustained declines ever observed:

Those are national, not global.
Globally, the fastest drop ever was 2020: ~6%, and it rebounded immediately.

That tells us something deep:

Anything faster than ~6% requires economic shutdown or collapse.

2️⃣ Why the system can’t move faster

The energy system is not software — it is steel, concrete, mines, refineries, ships, power plants, and grids.

Every year the world replaces only about:

• 2–3% of capital stock
• 1–2% of power plants
• ~3% of vehicle fleet
• ~1% of industrial furnaces

Even if every new replacement were zero-carbon (it isn’t), the maximum turnover speed caps how fast emissions can fall.

This is called capital stock inertia.

You can’t decarbonize a coal plant built in 2015 until it:

• wears out
• is forced closed
• or becomes uneconomic

That’s why energy transitions historically take 40–80 years.

3️⃣ What physics allows vs what politics promises

Let’s translate this into numbers.

Global CO₂ emissions ≈ 40 Gt/year

At 5% per year, emissions halve in ~14 years.
At 3% per year, they halve in ~23 years.

So realistic best-case:

Emissions fall meaningfully, but not fast enough to prevent overshoot.

4️⃣ What this means for temperature

This is where your climate-modeling work (FaIR, MAGICC) lines up with reality:

Even if we decarbonized at heroic speed (~5%/yr):

• CO₂ would keep rising for ~10 years
• Warming would keep increasing for ~20–30 years
• Peak temperature would overshoot targets

This is why negative emissions appear in every serious scenario — not because modelers love DAC, but because:

We can’t cut emissions fast enough to avoid overshoot.

5️⃣ The uncomfortable conclusion

Pure mitigation alone cannot stop near-term warming.

The real world allows:

**Gradual decarbonization (3–6%/yr)

• temporary overshoot
• eventual drawdown**

This is exactly why your instinct that CDR is fundamentally different from SAI is right:

• CDR works with carbon-cycle physics
• SAI tries to override climate physics

Mitigation can be fast — but not fast enough to replace atmospheric intervention if warming is already dangerous.

Impacts