The earth presents a circular cross-section to the sun. To a first approximation, the total power level of radiation it will receive from the sun will be given by:

    Total power, in watts received from the sun = s X S X p r²

where s is the coefficient of absorptivity of the earth's atmosphere (s is a number between 0 and 1 that tells what fraction of the sun's energy gets absorbed by the earth, while 1 - s would be the fraction that is reflected by the earth's white cloud layers and the earth's blue seas.), S is the solar radiation constant = 1,393 watts per square meter, and r is the radius of the earth, in meters. This simple formula will give the total amount of power falling upon the earth from the sun.

    In the meantime, the earth is radiating power back into the darkness of space at a total rate of:

    Total power, in watts re-radiated by the earth = s X 5.67 X (T/100)⁴ X 4 p r² watts.

    Now the earth is going to heat up until it reaches a temperature at which the amount of heat (or power) it re-radiates into space is equal to the amount of heat (or power) it receives from the sun. The amount of power it receives doesn't depend upon the average temperature of the earth but the amount of power it radiates does depend upon its average temperature--in fact, upon the fourth power of its absolute temperature. Notice also that the amount of area over which the earth receives power from the sun is p r², but the amount of area over which it can re-radiate that solar heat is 4 p r², or exactly 4 times as great. So the earth only needs to re-radiate 1/4th as much thermal power per square meter as the solar constant, since it has four times as much area over which to re-radiate it. One-fourth of 1,393 watts/meter² is about 348 watts per square meter. If we set 5.67 X (T/100)⁴ equal to 348, and solve it to find out what value for the earth's average global temperature we require to make the amount of power re-radiated by the earth equal to the amount of power it receives from the sun, we get a temperature of 280 degrees absolute (Kelvin) or about 7 degrees C or 44 degrees F.
    Of course, the situation is far more complicated than this. Local temperatures vary from night to day, from equator to poles, and from summer to winter. Clouds can reflect heat from the sun by day and can trap heat by night. Sunlight comes in at a color temperature of about 7,000+ degrees absolute... the temperature of the surface of the sun... and heat is radiated by the earth in the far infrared at a color temperature of 280 degrees absolute. Atmospheric conditions can block visible light by day while transmitting infrared radiation at night.
    My personal position on this issue has to do with the cost/benefit ratio. If global warming is thus and so much hot air (pun intended), a dastardly plot on the part of climatologists to garnishee more than their rightful share of the public and private purse, they will have succeeded in forcing us to curb our wanton dissipation of fossil fuels by switching to renewable energy sources earlier than would otherwise be necessary. The effect of climatologists snookering us will be (it seems to me) to advance our schedule to convert from fossil fuels to renewable energy sources. On the other hand, if global warming is anthropogenic and if it could possibly lead to a sudden climatic and/or ecological catastrophe, then we can't afford to let it run unchecked. So it seems to me to be a nolo contendre. Let's assume that global warming is anthropogenic. Let's advance our renewable energy research and implementation. It's going to be tough enough to get the world to give up fossil fuels even if everyone agrees that we should. What have we got to lose? (Anyway, that's been my reasoning about it.)