The galaxy rotation problem is basically this: Stars towards the edge of galaxies (mainly spiral galaxies) rotate much faster than they should based on Newtonian gravitation using only the visible material (the Einstein corrections are negligible at the speeds and distances being talked about, so they can't account for the differences). To explain this, you have basically two options: MOND, MOdified Newtonian Dynamics (ie., changing the laws of the universe at large distance scales like kiloparsecs), or dark matter (which can include baryonic dark matter as well, but generally refers to non-baryonic things), which corrects for it by assuming that there's a vast halo of objects that outweighs everything else in the galaxy and thus speeds up the rotation of objects far away from the galactic core.
The evidence at the moment seems to be in favor of dark matter, and in any event I have some doubt that we will ever see "examples at the same scale of pure baryonic matter interactions" as you put it; it may be that the phenomena in question are simply things that appear on the very large scale and aren't observable on the small scale, just the same way that relativity only becomes important under certain conditions and Newtonian dynamics works perfectly well in our "normal" world. (But I'm not an astrophysicist, just aiming to be one!)
Also,
Another impact structure in Siberia was created by an asteroid 100 km in size.
Er, what was that about reading comprehension, again?
Also, just because the Earth has feedback cycles that will (probably) keep us from turning into Venus doesn't mean the new equilibrium is something we will like. In this case, it's like the a/c is being set by someone you can try to influence, but not yourself...if you do it wrong (pump loads of greenhouse gases into the atmosphere--note that people are worried about CH4, NO, etc., too--the really powerful stuff), then maybe the a/c will be set to 90 degrees (Fahrenheit) and you'll get to enjoy sweating it out inside the house...
If the first is false, then there is no global warming. If the second is false, there is no way to prove the third, because we would have examples of the warming going past this point and then correcting. If the third is false, then we need take no action. If the fourth is false, then we need take no action. If the fifth is false, then any action we could take would likely be meaningless.
Your statements of the meaning of the second through fourth points are off. In actuality, (2) is known to have happened; it is known that (3) is not true (ie., that there are feedback cycles that can kick in to keep the Earth from turning into Venus); however even with (2) and (3) being that way (that there have been high temperatures in the past and that there are extreme feedback mechanisms in place) that doesn't mean there won't be catastrophic impacts. A comparison might be an air-conditioning system and a space heater. Suppose the air-conditioning system is much more powerful than the space heater. However, it takes a while to kick in. In the meantime, it will get awfully hot around the space heater.
What is the optimum temperature (or range) of the Earth?
This of course will depend on who you talk to. A polar bear will want it a lot colder than a tarantula, for instance. But for our purposes, it's fine to just consider human impacts. In that case, temperatures in the range of those we had when most of our current cities and population centers grew up would be best, as that would mean that none of them ought to end up frozen, flooded, or burning. So that means the average temperature in the period 1900-1950 or so.
When has it been at that temperature in the past?
Well, obviously 1900-1950. It has surely been at about that temperature at many other times, as we know that it's been hotter and colder than that at various points
Has it ever been outside that temperature in the past?
Yep. Loads hotter in the Mesozoic or Carbonaceous. Colder in the Little Ice Age.
How, specifically, do we know this?
Well, direct measurements for the latter. Palaeontological evidence for the first two, such as the presence of huge tropical swamps and giant insects in the Carbonaceous. I'm not a geologist or palaeoclimatologist, though, so I can't really describe the methods by which they figure the temperatures of historical periods that well.
In particular, how does one define the temperature of the Earth, and how does then measure that?
Well, like I said that's not my area of expertise. I'm perfectly willing to say that the people who DO have that as their area of expertise have doubtlessly thought about it a lot and come up with some good indicators, though, based on my experience in physics.
However, there's no practical way for him to get data that would allow him to conclude causation. With only one test subject, and presumably being aware of the differences between regular and decaf coffee, he cannot perform a blinded study. In this case, the best he can do (without getting very silly) is to look at the data, see if it has a strong correlation (which apparently it did), and examine if there were any confounding variables that might have altered. For example, he might have changed jobs from one allowing little sleep, and much of that irregular, to one allowing much more regular sleep, which might cause similar effects. In the event that there aren't any confounding variables he can detect, then that correlation is the best evidence he can get that whatever he happens to be doing (in this case, not drinking coffee) is better than whatever else he could be doing.
(BTW, the fallacy is actually reverse ad populum. After all, he was arguing that everyone not doing it meant it was better.)
Beware of Programmers who carry screwdrivers. -- Leonard Brandwein