Earth's "effective-surface" or "starting-surface" temperature (see note 1 below) is about -18° C, while its actual (on-average) surface temperature is about 14° C. The temperature difference is due to the heat retained by the Earth's atmosphere. Another way to look at this, is that the Earth's average surface temperature or "global warmth" is the combination of the Earth's starting temperature and its retained atmospheric heat. Of interest then, is how this "global warmth" changes over time; if it on average increases over a period of time, there is "global warming" over this period, likewise; if it decreases, there is "global cooling".
How much and how fast is "global warmth" changing, if at all, and are there any worse case scenarios? If so, under what conditions is a worse case scenario possible? For example, can "global warming" increase in a fast run-away like manner, such that reversing it is impossible, resulting in a condition where the Earth's surface eventually ends up like the surface of Venus, in a near molten-hot state, with all surface water evaporated? On the other hand, maybe there are no conditions under which this can occur.
With so much at stake, who can we depend on and who should we look to for reliable information and for making the best possible decisions; politicians, religious leaders, scientists, maybe fortune tellers? For example, more than half of the newly elected Republicans do not believe in Global Warming. Is this reasonable when the vast majority of scientists world wide now treat global warming as irrefutable scientific fact? Are these new Republicans so out of touch? How are they being influenced and by whom? If they act on erroneous information, then the decisions they make, or fail to make, can have disastrous environmental consequences for us all. If they make poor decisions now, the consequences of those decisions will be with us long after their political careers have ended.
With so much at stake, who should we depend on for guidance on how to proceed? If there's one thing we can depend on, it's that the Earth's climate, like with a hurricane or earthquake, follows only the laws of physics, and acts in a completely ruthless manner when the necessary physical conditions are present. Nothing else matters. It is very clear that human behavior changes conditions on Earth. The recent gulf oil spill is one example. The question is: will our accumulated actions lead to the setting up of the necessary physical conditions for a ruthless global-warming worst-case response?
Note 1: In general, a planets "effective-surface" temperature is its surface temperature if it absorbed all the radiation coming to it from its star and re-emitted all of this "black-body" radiation back into space.
Note 2: To convert Celsius to Fahrenheit, multiply the degrees in C by 1.8, then add 32. Example, -18°C = (-18*1.8 + 32)°F = (-32.4 + 32)°F = .4°F. While 14°C = (14*1.8 + 32)°F = (25.2+32)°F = 57.2°F. Likewise, to convert Fahrenheit to Celsius, multiply the degrees in F by 5/9, then subtract 32. (Also 1.8 = 9/5.)