Over the past 800,000 years, what was the highest natural CO₂ level, and what is it today?

Natural peaks reached ~280 ppm during interglacials. Today's level is ~420 ppm — 50% higher than any point in 800,000 years.

What is the difference in projected warming between SSP1-2.6 and SSP5-8.5 by 2100?

SSP1-2.6 projects ~1.8°C; SSP5-8.5 projects ~4.4°C. That's about 2.6°C difference, driven entirely by human emission choices.

Why does temperature sometimes appear to lead CO₂ in ice-core records?

Orbital (Milankovitch) cycles initiate warming, which causes oceans to release dissolved CO₂ (solubility decreases with temperature). The released CO₂ then amplifies warming via greenhouse effect — a positive feedback loop.

Pro 🔒~30 min

Climate Change Modeling

Historical temperature trends, CO₂ correlation, and future projections

How it works

Climate Change Modeling demonstrates a key principle: Ice-core records (Vostok, EPICA) show atmospheric CO₂ and temperature have been tightly coupled for 800,000 years, cycling between ~180 ppm (glacials) and ~280 ppm (interglacials). Ice-core records (Vostok, EPICA) show atmospheric CO₂ and temperature have been tightly coupled for 800,000 years, cycling between ~180 ppm (glacials) and ~280 ppm (interglacials). Since industrialization, CO₂ has risen to 420+ ppm — 50% above the highest natural level — driven by fossil fuel combustion and deforestation. The IPCC uses Shared Socioeconomic Pathways (SSPs) to project future warming: SSP1-2.6 (sustainable, ~1.8°C by 2100), SSP2-4.5 (middle of the road, ~2.7°C), SSP3-7.0 (regional rivalry, ~3.6°C), SSP5-8.5 (fossil-fueled, ~4.4°C). Key feedback loops include water vapor (amplifies warming), ice-albedo (less ice → more absorption), and permafrost methane release. The 'carbon budget' for 1.5°C is approximately 500 Gt CO₂ remaining.

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Step-by-step

Use the time range slider to zoom between recent centuries and deep ice-core history.
The red line shows global temperature anomaly; the blue line shows CO₂ concentration.
Select different SSP emission scenarios to see projected warming through 2100.
Notice how CO₂ and temperature track each other across glacial cycles.

Key formulas

$\Delta F = 5.35 \ln\left(\frac{C}{C_0}\right)$ Radiative forcing from CO₂: C is current concentration, C₀ is pre-industrial (280 ppm). Each doubling adds ~3.7 W/m².
$\Delta T = \lambda \cdot \Delta F, \quad \lambda \approx 0.8\,\text{°C/(W/m²)}$ Equilibrium temperature change from radiative forcing, with climate sensitivity parameter λ.

Frequently asked questions

Over the past 800,000 years, what was the highest natural CO₂ level, and what is it today?: Natural peaks reached ~280 ppm during interglacials. Today's level is ~420 ppm — 50% higher than any point in 800,000 years.
What is the difference in projected warming between SSP1-2.6 and SSP5-8.5 by 2100?: SSP1-2.6 projects ~1.8°C; SSP5-8.5 projects ~4.4°C. That's about 2.6°C difference, driven entirely by human emission choices.
Why does temperature sometimes appear to lead CO₂ in ice-core records?: Orbital (Milankovitch) cycles initiate warming, which causes oceans to release dissolved CO₂ (solubility decreases with temperature). The released CO₂ then amplifies warming via greenhouse effect — a positive feedback loop.