How do I figure out temperatures and amount of sunlight for a world?

Question

How do I figure out the temperatures of certain latitudes on a planet with factors such as sunlight and the emission of heat and energy from a planet's interior? Assume the planet is smaller than Earth and is warm enough that even its soil could be 80 degrees Fahrenheit, yet is still cold enough not to lose its oceans. These oceans can have a warmer oceanic crust and should be larger but shallower than Earth's oceans. The planet as a whole should have elevations like Venus with fewer areas of high and low elevation in comparison to Earth. Particularly when the planet has no seasons and should be tropical by Earth standards across it's surface?

Ex: how do I figure out the temperature of the tropics if the poles are as warm as our tropics?

Yes it does have plant life that uses H2O and photosynthesis.

And, as you can deduce if its poles are as warm as Earth's equator, then the planet does not need to orbit a different spectral type from Earth and can have a fairly similar orbit.

There is still the question of the planet having different plate tectonics but more volcanic gases which was lost from description. The atmosphere should have a very similar amount of nitrogen. I think oxygen would be affected by plant life and the increase in volcanic gases but shouldn't be dramatically high, at least in comparison to the history of Earth.

Answer 1

I think the climate is mostly influenced by the amount of sunlight that is absorbed.

• planet surface absorbs light - depends on the angle of incidence. If the radiant intensity of your sun has a uniform distribution, the same emission angle fraction has to cover much more area if tha angle of incidence is low (e.g. Earth-s poles)
• planet atmosphere absorbs light - depends mostly on the concentration of greenhouse gases and water in the atmosphere
• planet radiates some heat into space

In my opinion:

• warming one pole and keeping the equitorial temperature relatively low would be possible, if the rotational axis points towards the sun
• if the rotational axis is perpendicular to the the surface determined by the orbit, the poles would get c.a. equal light intensity, and the equitorial area much more than that

As basis, you could look up e.g. the mean summer temperature of one of the earth poles and some equitorial area, and use this difference on your planet.

But you could vary this with lots of things:

• mountains, hills, etc. have different incident angle than any flat surface
• plant life - trees evaporate water, but also cool the area around them
• albedo
• ocean currents could cool/warm areas

So in my opinion, you have a lot of freedom to choose the temperauture, that most fits your story.

Answer 2

Ok the mentioned brightness of poles and the equator from that nasa website would suggest 2.5 times the sunlight of earth and 0.632455532033676 au away from our sun. Yeah describing it as Venus like would make sense. So first we need to figure out what it's early atmosphere would be like and figure out whether cyanobacteria could exist and outgassing not prevent life from finding a way.