Transmittance spectrum around the dominant 15 μm (667 cm⁻¹) greenhouse band. Adjust sliders to see band widening as CO₂ concentration increases.
The blue curve shows CO₂ transmittance — where it dips toward 0%, CO₂ absorbs nearly all infrared radiation at that wavenumber. The dashed curve shows the pre-industrial baseline (280 ppm) for comparison.
The red zone at the band centre is already saturated — adding more CO₂ there captures no additional radiation. The amber wing zones on either side are not saturated: as CO₂ rises, the wings widen outward, absorbing wavelengths that were previously transparent. This is why greenhouse warming scales logarithmically with CO₂ — diminishing returns, but never zero returns.
Pressure broadening: lower pressure simulates higher altitudes, where fewer molecular collisions produce a narrower, sharper band.