ClimateOrbitOrbital forcing · seasonal climate · attribution

Insolation explorer

What the orbit does to sunlight

Pick any epoch in the last million years, or build an orbit by hand, and compare its top-of-atmosphere insolation with today's at every latitude and every day. The numbers are computed live with the same formula the analysis uses.
Annual mean at 65°N211.1 W m⁻²−2.70 vs today
Brightest day440 W m⁻²−37.6 vs today
Caloric summer half-year351.4 W m⁻²−15.2 vs today
Perihelion date12 Jantoday: 3 Jan

Daily-mean insolation through the year at 65°N

Today versus 115 ka BP

  • Today
  • 115 ka BP
Top-of-atmosphere, S₀ = 1360.8 W m⁻², computed in your browser with the same Berger (1978) formula as the analysis, verified against the Python implementation to 10⁻¹² W m⁻². Calendar anchored to the modern March-equinox date.

Insolation change, 115 ka BP minus today

Every latitude, every day of the year

W m⁻²
−610+61
Latitude
Day of year
Hover a cell, or focus the map and use the arrow keys, to read a value. Differences mix two effects: the Earth–Sun distance and, through Kepler's second law, the calendar dates on which each solar longitude is reached.

Reading the change map

At 115 ka, perihelion fell near the December solstice while eccentricity was high, so northern summer sunlight at 65°N was tens of W m⁻² below today's. That is the configuration Milankovitch theory associates with glacial inception. The change map also shows that the global annual mean barely moves (it scales as 1/√(1−e²)): orbital forcing mostly redistributes energy in latitude and season rather than adding it.

Validation targets met by the underlying code: 65°N June-solstice insolation of 479.3 W m⁻² on the S₀ = 1365 convention (literature: 479–481), a numerical global mean within 1.6×10⁻⁶ of the closed form, and agreement to 0.02° between two independent solar-position calculations.