I will provide part of an answer here.
Most people intuitively think that if the Earth warms, the temperature will rise. That intuition is largely wrong, because Earth is not a perfect sphere of a global ocean, and it is an aqueous world. Water behaves in a peculiar way. Unlike many substances, which go from solid to liquid to vapor as the temperature rises, water has a temperature at which solid, liquid, and vapor can all exist at the same time, called the triple point (about 0.01 C) https://en.wikipedia.org/wiki/Triple_point and introducing heat into the system does not raise temperature on the average, but causes a shift from some of those phases into the others, while the general average temperature doesn't change much. The following diagram is intended to illustrate that behavior.
The important thing about the Earth is that the average temperature is fairly close to the triple point. Adding heat can cause ice to melt into water, or either of those phases to evaporate into vapor. It is only when almost all the water is vapor that temperature can begin to rise greatly enough to threaten habitability. Of course, water vapor is also a greenhouse gas, so that can cause an even greater rise.
Nothing in the geological record indicates that such a runaway rise has ever occurred. Water has always acted to buffer temperature changes within a fairly narrow range. We can speculate that enough heat, together with the sublimation of deep-sea methyl clathrates, together with releases of methane and CO2 from melting tundra, might combine to produce runaway temperature rise, but that is only speculation, without geological evidence. One would expect that if it had a significant chance of occurring, it would have done so at least once in Earth's past.
That of course does not mean it may not occur in Earth's future. In the far distant future we can expect it to occur as the sun expands and grows hotter.
So what we can expect from global warming is the melting of ice, the rising of sea levels, and more clouds with more rainfall. That is also likely to result in more stormy weather, with more flooding and wind damage.
Now because Earth is not spherically symmetric, and there are irregularities on the surface, we can expect average surface temperatures to rise seasonally over land, causing seasonal changes to shift toward the poles and occur earlier as the process unfolds. The great deserts that encircle Earth are likely to shift toward the poles, causing the desiccation of now green areas and increases in widespread forest and grass fires. Once fertile land may become infertile, and infertile land may become fertile again after a span of thousands of years. North Africa and the Levant were once green, about 6000 years ago, before the desert band moved northward.
Here is a diagram of global air circulation and precipitation:
There are two world-circling desert bands at about latitudes 38o N and 38o S, where the northern and southern Hadley cells meet the Mid-latitude cells. https://en.wikipedia.org/wiki/Hadley_cell The general airflow there is downward, resulting in drying, Where warm air rises, it cools and produces more rainfall. The bands are somewhat broken by terrain features, especially in North America. In the southern hemisphere the only land masses at 38o S are parts of Africa, Australia, and South America, and the first two have deserts there. The circulation cells can shift toward or away from the poles, causing the desert bands to shift under them.
So is this global warming/climate change caused by human activity? Much of it is, although coal fired power plants and automobiles may not be the main sources of CO2. The isotopic abundances of the carbon in atmospheric CO2 indicate much of the source is fossil fuels. But much or more of it may come from things like the tilling of topsoil, causing it to oxidize, from runoff of topsoil into the oceans, the burning of grassland and forest, and other such activities over which public policy doesn't have much control. Even if the developed countries were to stop producing industrial CO2 altogether and go entirely to wind, solar, and other "green" sources, it would make little difference. China alone would overwhelm the rest. The notion that we can influence other countries by "setting a good example" is ludicrous. They would just laugh at us. Low cost trumps good reputation.
Are we avoiding a new ice age?
The precise causes of the last several ice ages (about five) are not well understood, but a simple extrapolation from the past few suggests that we may be about to enter a new one. If so than greenhouse gasses may retard it, and we may even want to produce more such gasses. Another ice age would not be an extinction-threatening event, but it would certainly be traumatic and disruptive, perhaps more than presently projected "climate change" is likely to be. We may want to achieve some control over both tendencies.
Lower sea levels
In the past sea levels have also been as much as 300 feet lower. For example, about 5.33 million years ago the Mediterranean Basin consisted of two landlocked seas, in what has been called called the Messinian era. Then the rising Atlantic broke through tat the Strait of Gibraltar and filled the basin in as few as two years, rising as fast as ten meters a day, in what has been called the Zanclean Deluge. See https://en.wikipedia.org/wiki/Zanclean_flood . More recently, it is hypothesized that the Aegean Sea broke through the Bosphorus Strait about 7400 to 5600 BC to fill the Black Sea to its present level. Some speculate that the resulting inundation gave rise to the myth of the Great Flood. https://en.wikipedia.org/wiki/Black_Sea_deluge_hypothesis . Another explanation for that myth is the evidence of an asteroid or comet impact in the Indian Ocean about 5000 years ago that created the Burckle Crater. See https://en.wikipedia.org/wiki/Burckle_Crater . The tsunamis created by such an event might have been funneled by the Persian Gulf to produce especially high flooding in the lower Mesopotamian basin.
So could sea levels rise as much as 200 feet? Yes. In the past they have been that high. That could inundate low lying coastal areas like Bangladesh, Florida, and the Netherlands, and perhaps even the northern part of the Central Valley of California. It may not be a good time to invest much in coastal cities, resort property, or low lying islands. China may have its new Spratly Island base flooded.
Interestingly, Mars is also close to the triple point of water. There is no liquid water on the surface because the atmospheric pressure is too low. If we could raise the pressure, there appears to be enough water locked up in the soil or at the poles to form some lakes or small seas. For more than that we would need to gather icy comets from the outer Solar System, deflect them toward Mars, and vaporize them, perhaps with a thermonuclear device, as they approach that planet, and merge with the Martian atmosphere. It requires surprisingly few such objects to give Mars an Earthlike atmosphere (except without as much O2).
So what is to be done?
Trying to cap greenhouse gas production in the few nations with legal systems that might enforce restraints is almost certainly a wasted effort, no matter how much it may make some feel good to try it.
No, the only thing we can do is to develop alternative energy sources cheaper than fossil fuels. There are two likely sources: thorium nuclear plants, and solar power collected in space, probably on the Moon, and beamed to earth. See http://energyfromthorium.com/ and http://lunarsolarpower.org . We need to develop test systems for both, to weigh further investment.