you missed the point
adornoe, the Romans would have told you that the sahara was mostly green in the north (they wrote about it), they hunted lions and leopard and antelope there less than 2000 years ago. There were bears in Libya. The Egyptian Nile civilisation started its rise around 6-7 thousand years ago after the land further to the west became too dry to support many people. They had to move. We know this because they left their burials grounds in what is now the deep desert. NOTE THAT Global warming did NOT cause these changes. And that's the point: it's not that global warming caused these things, it's that those places were quite heavily populated then, and aren't now, because of the changes. Change comes, and when it does, civilisations fall, and people have to move or die, and when they move, if there isn't empty land to move into, there is conflict. If you think that this isn't going to be difficult to cope with, you're wrong. If you think it wouldn't be worth your while to try to avoid it, you're wrong. What global warming will do is force these changes on us, and rapidly. And the main thing is that these changes, unlike the localised changes that have always been going on, will be happening everywhere at the same time. This isn't the same kind of climate change as has always been happening, where it gets warmer, wetter, or drier in some parts of the world and cooler, drier, or wetter in others over intervals of thousands of years. This is everywhere at once, and much steeper, much quicker (over the next century). We are already seeing crop yields fall in the unlucky parts, including North America. The world price of wheat is 40% more than it was a year ago. The price of corn is nearly three times what it was four or five years ago. What if North America has another year like the last? Fires and drought. How many repeats of that before the price of wheat or corn is out of most peoples reach?
But we're too stupid to even try to avoid it, it seems, and it IS avoidable. Too lazy to change, even if it kills us.
And who told you Greenland's ice melted in the middle ages? That's complete nonsense. Only the southern coastal tip of Greenland has been habitable for farming people in the last few hundred thousand years. The Viking settlements in the early middle ages just managed to hang on while there was a temporary warming (caused by volcanism, it's thought - all that dust in the high atmosphere keeps the heat in, see?) which lasted around 150 years. This meant the coastal plain was free of ice to a few miles inland for a while. These people never had an easy time of it. When this changed and 'the weather' went back some way to what it had been for the prior few thousand years, they starved, because they were farmers, not hunter-gatherers like the Inuit. Greenland is buried under more than a mile of ice for the most part, two miles in places, and has been throughout human history. In the depths of the last ice age 25000 years ago, global sea levels were 250 feet below where they are now. If people had had any kind of civilisation on the coastal plains of that world (we do like to live near to large rivers), they would all have been submerged and we would never have known they existed.
My point was that such changes are extremely disruptive and very hard to get through. Faced with shortages, people kill each other. Those that don't try to move and are not prepared to fight to live, starve. Do nothing to avoid what's likely coming IF we do nothing, and millions, and probably tens or hundreds of millions, will die before their time. It won't be pretty.
People rave about illegal immigration now - wait until there are hundreds of millions of people trying to move to the parts of the world where it is still possible to have a decent life. You wouldn't want to be there.
And why are you so wedded to burning oil ? We've only been doing it seriously for a hundred years or so. My Dad was born in 1907 into a world where only a very few rich people had a car, where you bought gasoline by the pint in the local Pharmacy! And it was only 200 years before that, that we started burning coal in any real quantity. We know how to manage without these things now. We have other better ways to get energy, and they don't produce CO2. The sun supplies more energy than we will ever need, if we gear ourselves up to collect it, and we know how to produce nuclear power too. We should be doing both. Oil is too precious and useful a material simply to burn it. Sell your shares in Amoco or Texaco or BP or whatever and buy into solar and nuclear. You will make a fortune (eventually, when enough people realise it's the only way to go).
And by the way, the sahara wasn't a desert at all 8000 years ago, except in what's now the deep centre in the south. There's still a hell of a lot of fresh water under it, but it's a mile (or two) down and being depleted rapidly by human extraction - satellite photos make it very clear where the many rivers used to flow, and a lot of them still do flow, but deep in the sand, not on the surface - where do you think the deep (artesian) wells get their water from?