Stopping our emissions wouldn't help. We would have to create negative emissions. We don't have that technology.
There are routhly 700Gt of CO2 in the atmosphere today and roughly 0.0384% of the atmosphere is CO2. The atmosphere is roughly 5,000,000Gt. This puts the average mass at over 3 times that of CO2.
Humans release roughly 8Gt of CO2 per year through industry, farming, etc. Compare this to:
* volcanic activity releases less than 1% of this much.
* Decomposition of organic matter in nature releases ~220Gt/year
Animals also naturally produce CH4, though, over 5 year periods, natural CO2 sinks balance out natural CO2 sources. This is mostly due to live plant biomass decreasing CO2 in the air.
None of the natural CO2 comes from anything other than already existing carbon. Remember, you can't create or destroy matter? Nature doesn't have the ability to change one atom into another atom except through radioactive decay.
SO, you'd think as CO2 goes up, plant mass might go down?
Except, free carbon is increasing. Why? Our consumption of fossil fuels is accelerating this expulsion of sequestered carbon at a faster rate than natural forces can bury it under rock and ocean.
Nature tries hard. It is estimated that only 45% of the human contributed CO2 emitted contirbutes to the increase in atmospheric levels. Existing natural CO2 sinks take care of 55%.
So about 3.6 gigatonnes of CO2 accumulate in the atmosphere per year due to human activities.
As more CO2 is emitted into the atmosphere, the earth warms. This is common and natural. Warmer planet means more water vapor in motion. More free carbon means more biomass could be grown. yAy, so what's the problem? It should slow down, balance out, right?
Not exactly. As the Earth warms, the polar ice melts. As ice melts, reflective surface of the Earth decreases. We call this a positive feedback loop. As it gets warmer, it becomes easier to continue warming.
There's another positive feedback loop. Let me explain. 55million years ago, the polar regions were semitropical. CO2 levels were 5x what they are now. The deep ocean currents would circulate warm, tropical water, just like our atmosphere does for air. The sea floor had temperatures upwards of 38C in places (100F).
Again, get to the point? Well, the tropical north pole region was an ocean with a thin layer of low-salt content over the top of a dense layer of high salt content. Freshwater ferns grew across this and as they died, the biomass sunk and got buried. We call this "sequestering of carbon" because it took the carbon out of circulation. This activity was responsible for the decrease on CO2 and the cool-off that allowed the poles to be frozen.
The plant matter didn't just amount to oil trapped in sediment. Bacteria converted large amounts of it into methane. That methane is trapped in ice. Because of the huge pressures at the ocean floor, that ice will stay solid to about 18C if undisturbed.
When this melts, each cubic foot of "methane clathrate" will release 186 cubic feet of methane. It's projected that the arctic regions contain 500 to 2500 gigatonnes of methane. (422.62kg/m3 if you want to do the math).
What's worse is that the methane clathrates form boulders which cap methane wells. As they dissolve, large pockets of methane will bubble up.
Methane displaces oxygen, so this could create asphyxiating clouds, but eventually, they would mix with the atmosphere.
As things stabilized, the O2 concentration would drop substantially, killing off many of the more fragile life forms, and making high altitude operations more difficult for mammals.
If all of this were released, CO2 levels would be 0.192%, plus methane may be released up to another .137%. As it decomposed, it would bind up 2 oxygen molecules per methane molecule, reducing free oxygen by .274%.
Remember, methane's useful existence in the atmosphere is about 8.4 years. Another .3% oxygen would be eaten by the breakdown of CH4.
Overall reduction of percentage of oxygen by volume would be around .8 to .9%. Current O2 levels are 20.9% by volume. Therefore, O2 could drop to around 20% by volume. Reduction below 19.5% would result in asphyxia at sea level.
Adaptation for high altitude is unknown, but at sea level, we could still survive, though our energy levels would be lower until we adapted.
All of this excludes the fact that already, as permafrost is thawing, ancient bogs have resumed production of CH4.
Now, the changes 55 million years ago which sequestered carbon over 100,000 years. But when the threshold was reached, the changeover occurred quickly, in just a few stairsteps, but the biggest changes were too fast to show up in the scale.
Remember that methane warms the Earth in 8.4 years as much as 25 times as much CO2 does in 100 years, and then breaks down into CO2 for another 100 years of warming.
It is unknown specifically how rapidly the earth will warm; however, it is possible that the tropical regions could reach up to 45 degrees latitude and the poles could reach average temperatures of 7C.
The only possible trump card I can think of would be, due to additional mobilization of water vapor, a chance occurrance of a large snow storm covering a large amount of land, could possibly tip the scales. However, this would also halt biomass generation and unless humans were killed off substantially, we would simply continue the warming as a self preservation method. This all gets fuzzy.
In summary, we are likely past the point of no return. Our planet is finishing a deep cycle cold spell. Several positive feeback loops have begun to warm the Earth. We are ONE of those. We lack the technology and the willpower to change any of this withink the timeframe that we COULD reverse the warming trend.
I think continued progress on efficiency is a generally good thing for a variety of reasons. I think continued research into solar energy collection is also important, since that's ultimately the root of our energy here. I think interstellar travel, and many of the other sci-fi technologies will rely on high density energy sources such as antimatter, which should be manufactured from solar energy in high orbit for efficiencies and safety.
I don't have a bibliography. References were wikipedia on the earth, atmosphere, methane, co2, oxygen, clathrates, and general google searches on tangents. I urge you to learn enough for yourself to get a big picture.