We can do very rough order of magnitude calculations to see the problem. Let's say, worst case scenario, we dump enough CO2, CH4, CFCs, PFCs, sulfohexanes, and water vapor into the atmosphere to warm it 10 C in the next 50 years. This would, by most accounts, qualify as catastrophic climate change. Let's assume we changed the atmospheric chemistry all at once, for simplicity of calculations.
According to Wikipedia, the Earth's atmosphere weighs 5e18 kg. Let's assume the specific heat is 1039 J/kg.K, equivalent to N2 gas. This is equivalent to capturing 5E22 joules in the 50 years, or put another way, it is equivalent to having an electric blanket over the entire earth heating at a rate of about 3E13 watts. It's probably several times bigger, actually, because the oceans and crust will also warm (not as much, but they are far more massive), and the earth will radiate at a slightly higher level. Let's say 1E15 watts is a reasonable estimate. It doesn't change the argument.
Why is this important? Current human primary energy generation functions at the rate of about 16 TW, or 1.6E13 W. This rate has been doubling very roughly every 25-40 yrs for the past century - actually, it doubled very quickly when a country goes through its industrial revolution, then more slowly afterwards. Much of the world is about to go through or is going through mass industrialization now, so let's say the average is 30 years for the next couple centuries. Again, because we're dealing with exponential functions, it doesn't change the conclusion, only the date. For reference, K1.0 is 1E16-1E17 W of primary energy available, or about 1000x what we use today, but we will have to be able to control the Earth's climate well before then.
The reason why is that all primary energy eventually turns into heat. Some of it goes to lifting building materials, some goes into light to which the atmosphere is transparent, but most of what we create goes in short order directly to heat. Power plants dump heat in water bodies and cooling towers, power lines radiate resistive heat, pumped water falls downhill to water crops, light bulbs and computers get hot, cars, trains, boats, and airplanes rub against the ground, water, and air. Even if there is no greenhouse effect, in less than a two centuries (179 years by the figures above), humankind will be producing 1e15 W of primary energy. It seems like a long time, but 200 years is about two long human lifetimes. It is conceivable that children alive today will know people in their old age who will be alive then. It is likely that most of the nations of the world will have similar names, cultures, norms, and borders in 200 years. It is highly unlikely that any drastic change in human nature will occur.
This is, of course, Malthusian, and Malthusian arguments usually run up against scarcity. But what scarcity is there in energy? We can reach 1E15 W with proliferation of breeder reactors, which are currently operational in Japan and France. We can probably get there on coal, oil shale, and oil sands. We can definitely get there with methane hydrates. Minerals are unlikely to run out in that time; we have barely scratched the surface of Earth quite literally, and there is a molten core of iron below our feet. And keep in mind that this energy level threshold is vastly overstated; it is merely the energy required to heat the Earth's atmosphere 10 C in 50 years (along with the crust and oceans to a lesser extent). We start having warming noticeable in a human life span, say 1 C/century, after less than two doublings, or about 50 years off. 50 years! That's about how long it has been since the concept of global warming came about. 50 years ago man had put satellites in orbit and detonated the H bomb. Mix in some greenhouse gases, a big volcano or two, and a couple solar maxima, and you are likely to get some short-term equivalent that looks awfully scary well before that. It is entirely conceivable that we had just that in the 1990's, with a record-setting solar maximum.
So I am not denying anthropogenic climate change. On the contrary, I am saying it is inevitable. Even with the cleanest possible energy, it will start happening within most of our lifetimes simply from the waste heat of civilization. Atmospheric carbon is the canary in the coal mine. We could completely fix that problem by, say, switching over to breeder nuclear reactors or bringing fusion power and electric cars to maturity. However, that would only delay the problem. Energy efficiency can slow the process, but it only (slightly) postpones the date. A global dark age might put it off indefinitely, but then we'll have bigger problems; and depending how far civilization regresses it could make things worse - imagine an 1880s-level civilization of 15 billion people, burning coal and having babies at an alarming rate. It has taken some 25 years to get some form of somewhat functional carbon legislation passed in Europe. Optimistically, it will take another 25 to do similar things around the world. By then the problem will have moved on.
We do have to learn how to control the level and mix of gases in our atmosphere. I suspect this will come mainly when urbanization and industrialization re-greens most of the Earth as it has done in the US and Europe, and when genetic engineering creates versions of today's plants and algae that are extra good at sequestering carbon. However, this is not enough. We need to be able to engineer the heat budget of the Earth writ large. We are near the lower limits of atmospheric greenhouse gases, water notwithstanding since it is important to keep at a certain level for rain. Our other options are not very numerous.
- Move energy generation off-planet - this helps get rid of the 20-50% of the heat that comes from power plants themselves, but doesn't change the fact that all the rest is dumped into the biosphere. In other words, it changes the date but not the conclusion.
- Capture and dispose of waste heat - this might be done by using heat-loving microbes to create chemical compounds in endothermic reactions, which would then be shot off-planet and burned elsewhere, with the ash returned. This is horribly inefficient, and requires relatively high-quality heat.
- Move the Earth away from the sun - this is well beyond the capabilities of a K1.0 civilization, simply put.
- Limit solar insolation - this is the only real alternative. The possibilities range from the near-term (painting roofs white, cloud seeding), to the far-off (massive sunshades, breaking up asteroids to make rings, reflective mirrors).
Controlling the atmospheric composition is one ingredient for a K1.0 civilization to master, but it is a fine-tune knob. We are making barely-perceptible changes to Earth's climate, but I don't think people realize just how soon those changes will become inevitable and very apparent, and through what means. I don't believe politics can do much more than create awareness and change local output; technology and demographics are, as always, the major factions here. The current focus on limiting carbon emissions through regulation is hype at best, and head-in-the-sand hand waving at worst.