Two competing effects drive global-mean temperature. Greenhouse gases add a logarithmic forcing as CO₂ rises above its 1750 baseline of 280 ppm:
ΔF_GHG = 5.35 · ln(CO₂ / 280) [W/m²]
Aerosols do the opposite: sunlight falling through a haze layer of optical depth τ is attenuated by Beer–Lambert extinction, and the scattered/absorbed split depends on the single-scattering albedo ω₀ (near 1 = pure scattering, e.g. sulfate; well below 1 = absorbing, e.g. soot):
Transmission T = e^(−τ)
Surface solar = (S₀/4) · T, S₀ = 1361 W/m²
ΔF_aerosol ≈ −F₀ · τ · (2ω₀ − 1)
When ω₀ is close to 1 the aerosol layer mostly reflects sunlight back to space and cools the surface — this is the historical "global dimming" measured by sunlight sensors from the 1950s onward, at its strongest in the 1970s–80s as sulfate pollution from coal and oil peaked. Clean-air laws (US 1970, EU/China later) cut SO₂ emissions and optical depth fell, so more sunlight reached the ground again — "global brightening" — which unmasked greenhouse warming that had been partly hidden underneath it the whole time. When ω₀ drops below 0.5 (soot-heavy smoke, which absorbs far more than it scatters), the sign of ΔF_aerosol flips and the haze layer adds warming instead of cooling.
- Year slider / Play — steps through a schematic 1950–2020 history of atmospheric CO₂ and aerosol optical depth built from published dimming/brightening and ice-core/Mauna Loa records.
- Aerosol type — sets ω₀: sulfate ≈0.98 (near-pure scattering), soot ≈0.35 (strongly absorbing — real-world black carbon is typically ω₀≈0.2–0.4, well past the flip point), mixed ≈0.85.
- Manual optical depth / manual CO₂ — override the year-driven history so you can test any haze thickness or any greenhouse-gas level directly, independently of each other.
- Falling dots are photons: gold ones punch straight through to the ground, pale ones scatter back out of the haze band, and dark red ones are absorbed inside it and fade — the ratio between the three tracks T and ω₀ live. Drag the scene sideways to pan the view.
Real-world relevance: the IPCC's best estimate of present-day aerosol effective radiative forcing is roughly −1.1 W/m² (net cooling), meaning aerosols have offset a meaningful share of the ~2.9 W/m² added by greenhouse gases since 1750 — one reason warming has not yet caught up with the full committed forcing.