Caption: Albedo as a percentage as a function of Earth land cover (i.e., surface type) and cloud type.

Features:

1. Albedo (common symbol α: see, e.g., Wikipedia: Albedo:White-sky and black-sky albedo) is usually given as a decimal fraction.

   Albedo can be given in The percentage form in which case it is the decimal fraction form times 100 %. This what the image uses.

   In the analysis below, we use symbol α for albedo and the decimal fraction form---and NOT the percentage form.

2. The displayed land covers are as follows:
   cirrus cloud, crops, desert, forest, ice, meadows, sand, Savanna, snow, soil, stratus cloud, water.

3. Effective temperature is a fiducial-value temperature for a spherical body (e.g., star, planet). It is the temperature the body would have if it radiated its non-reflective luminosity like an exact blackbody radiator.

   If the body is approximately a blackbody radiator, the effective temperature is approximately the actual surface temperature, and so is a good characteristic or sort of average temperature. If the body is NOT approximately a blackbody radiator, the effective temperature is still often a useful value for characterizing the body particularly for comparison to other bodies.

4. We can do a derivation of a useful formula for the effective temperature of planets.
   1. F = L/(4πr**2) : The formula for flux from an isotropically radiating star of luminosity at distance r from the star. It is an inverse-square-law formula

   2. P = πR**2*F : The formula for the power captured by a planet of radius R at distance r from the star.

   3. f = [P/(4πR**2)]*(1-α) = σ*T_eff**4 : The f is the average power per unit area absorbed into the heat energy of the planet---the reflected electromagnetic radiation (EMR) is removed by the factor (1-α)---and we have equated it to the Stefan-Boltzmann law for the flux radiated by a blackbody radiator at temperature T_eff which is, of course, the effective temperature of the planet.

      The Stefan-Boltzmann constant σ = 5.670367(13)*10**(-8) W/*m**2*K**4).

   4. Solving for T_eff gives

          T_eff = {[L/(16πr**2*σ)]*(1-α)}**(1/4)

      or in a fiducial-value formula

          T_eff = ( 278.33000 K )* (L/L_☉)**(1/4)*(r_⊕/r)**(1/2)*(1-α)**(1/4) ,

   where solar luminosity L_☉ = 3.828*10**26 W and Earth's mean orbital radius r_⊕ = 1.000001018 * 1 AU (epoch J2000 and astronomical unit (AU) = 1.49597870700*10**11 m, and where more than significant figures are given for the fiducial-value formula to allow tests of reproducibility.

   The formula agrees with the one given by Wikipedia: Effective temperature: Planet.

5. Using the above formula, we determine the following effective temperatures for the inner-Solar-System planets: Mercury ☿, Venus ♀, Earth ⊕, Mars ♂.

   _______________________________________________________________________
   Table:  Effective Temperatures for the Inner-Solar-System Planets
   _______________________________________________________________________
   Planet   R_orbital_mean    α_b    T_eff   T_eff   T_(mean/fiducial)
                                      α=0     α_b  
                 (AU)                 (K)     (K)          (K)
   _______________________________________________________________________
   Mercury    0.387098       0.068   447.4   439.5  100 (night), 700 (day)
   Venus      0.723332       0.90    327.3   184.0         740
   Earth      1.000001018    0.306   278.3   254.0         288
   Mars       1.523679       0.25    225.5   209.8         210
   _______________________________________________________________________
   

   Note: The α_b is the bond albedo which is the appropriate planetary albedo for calculating effective temperature.

6. The effective temperature can only be a crude average temperature if the planet has extreme day-night temperature variation like Mercury. Recall the Mercury's synodic day (i.e., solar day) is 176 days which is almost twice Mercury's orbital period 87.9691 days and almost 3 times its sidereal rotation period 58.646 days due Mercury's 3:2 spin-orbit resonance. It's a long cold night on Mercury of ∼ 88 days.

7. The effective temperature departs increasingly from the actual average temperature with increasing greenhouse effect.

   Venus has an extreme greenhouse effect and Earth a moderate one.

8. What would be planet's average temperature with the greenhouse effect turned off?

   That depends on what other counterfactual assumptions you make?

   For example, if you turn off the greenhouse effect for Venus, but keep its bond albedo α_b = 0.90, then Venus will have a very low average temperature closely approximating the effective temperature 184.0 K given in the table above.

   But Venus's greenhouse effect is caused by Venusian atmosphere which also gives Venus its high bond albedo.

   Without the Venusian atmosphere, Venus would probably have a bond albedo similar to that of the Moon 0.136. Then Venus would have probably have an average temperature an average temperature closely approximating the effective temperature 327.3 K given in the table above.

9. Because the relatively short Martian day = 25h,39m,35.244s) (causing very small thermal inertia) very thin Martian atmosphere (causing very little greenhouse effect) and relatively low bond albedo (which roughly appoximates zero), Mars's actual average temperature closely approximates the effective temperatures given in the table above.