Why don't you think we can modify the earth's climate? We know for a fact that volcanic eruptions cool the earth, by spraying sulfur dioxide into the atmosphere. We can even measure how much sulfur dioxide they emit and how much it cools the earth.
The smokestack idea in the OP is the same concept...it would just be humans doing it instead of volcanoes. So I'm unclear as to why you don't think it would work.
A Volcanic eruption is far greater than anything man can concoct; but let me make my point painfully clear about this farce called "man caused" global warming.
First let's all be clear, the debate is the farcical notion that this is "man caused" not about Global warming. We all know and readily acknowledge that for centuries the earth has been experiencing a warming trend.
How do we know this? Well for one thing, in the great State of California where we have a fantastic park called Yosemite, the scientists tell us that the massive granite formations we are looking at were formed by massive glaciers that retreated millions of years ago leaving much of what we see today.
Now someone with a modicum of intellect and intelligence might ask whatever it was that caused the massive melting that caused the glaciers to retreat, not just from the USA, but from the entire country of Canada way back before man was even a major part of this world?
The TRUTH is that there is believed to have been at least FOUR other major warming and cooling trends long before man was ever evident.
At least seven ice ages have been recognized. At least four of them are considered significant because of the extent of their glaciation or because they lasted for an extremely long time:
about 2 million years ago to the present—the Quaternary Ice Age
350 to 250 million years ago—the Karoo Ice Age
800 to 600 million years ago—the Cryogenian (or Sturtian-Varangian) Ice Age
2400 to 2100 million years ago—the Huronian Ice Age.
The FACT is that this farcical myth being perpetuated by primarily Librul self proclaimed "environmental scientists" and is nothing more than an effort to fear monger people into behavior that will not only result in the economic decline of our economies, but perhaps even the starvation of millions should they get their way. These are the same scam artists that in the 70's gave us the "chicken little" claims of global cooling.
I am sure these con artists like Al Gore, the dumbest man in America, are passionate in their beliefs; but their science is MORE than suspect.
The SUN is the single BIGGEST culprit in this cooling and warming and has been expressed by many scientists for decades but conveniently ignored by those attempting to promote this "inconvenient" lie about man caused global warming.
I would be more afraid of a massive trend in cooling than I am about warming. At least with warming many areas formerly inhospitable in the Northern hemisphere will be more adaptable to crop growth to continue feeding a growing population.
P.S. it is not just that I don't think that man can modify the earths climate; but also that it would be extremely dangerous to mess with the complex equilibrium that ecompasses this planet. Here's a thought: the water we drink is the same water dinosaurs waded and pissed in.