First I'll say the bit about the population. Looking at it as humans giving off body heat causing problems is nonsense. The heat we generate is so insignificant to other problems. At the same time does population have an affect? Yes, of course. The more people there are, the more energy is consumed. And depending on where that energy comes from, has a negative impact.
Now I personally don't think the term global warming is what it should be called. Because really what it boils down to is our environment is changing faster than we expected. Our climates and seasons are changing. And if you don't think so you're either blind, or don't live in a region that shows it(yet). In the last 5 years or so weather here has become worse and worse. We've gotten snow in what would be considered late spring. We've had weather so nice you could walk out in shorts and a t-shirt in the middle of winter for days. Where I live that's unheard of. Seasons seem to come sooner or far later than they use to in the past. Which 5-10 years ago were far more predictable. SO the earth is changing, whether you agree with it not. Call it a phenomena or global warming, it doesn't matter. Because both are happening. Yes the earth goes though natural changing processes. But these changes take hundreds and thousands of years to normally take affect. Humans are kicking it into overdrive.
Now why is this all happening? Is it the fact that the industrial revolution kicked of our pollution to date, in staggering numbers? You bet it is. But that is human nature. They don't think of what will happen down the t line. they are content with right now, and don't care.That isn't to say its the ONLY reason though. There are many. Earth has a natural filter that cleans our air. You know what that is? Its our forests. And how much do we have left? Very little compared to 300+ years ago. Plant live takes our bad carbons we put into the air and exchanges it with oxygen. You take something like that away with increasing the bad emissions. Troubles are bound to happen.
Can it be reversed? Well scientists say that even if we were to stop all emissions right now, it would take hundreds of years for the planet to correct itself.
How can we help? There are MANY ways people can help. From a country standpoint. China isn't doing anything for the goo. They have plans of adding tens if not hundreds of new nuclear and coal plants for the demanding energy consumption, where as other countries are looking into other forms of energy. This isn't just your planet its everyones. And if everyone doesn't get involved than nothing is going to help. China will offset anythign we do.
What can be done though? So many things. Big and small. We can stop being depending on harmful energies. Cars could be run on hydrogen which can be directly made from water. Houses can be run off wind mill farms, and solar energy, hydro electric power as well. Appliances that use propane can be replaced by electric ones. Plastics consumption can be switched to biodegradable things. Better ways to get rid of waste. Instead of putting it back into our limited fresh water sources(which aren't really all that "fresh" anymore). There's an answer for everything we do that we shouldn't. The problem isn't how its when, and how much. Though, how much shouldn't be in question. I think if you have any respect for the plane you live on then you should do your part to take care of it. Unfortunately the stuff that really matters is the big things, and those are things that most people wont have parts in, it will be the governments.
Personally I think we need to move to solar energy now instead of later. I don't know how many people realize how much we really need. If less than 5% of the United States area was filled with solar cells, we'd have enough free energy to power our entire country. But unfortunately we do everything when we're forced to. Not when we should. In either case, just do your share. Don't continue thinking you're better than everyone and you don't have an impact. small or not, you do. and all those little impacts add up.