Just the heat output from humans running engines, electricity, etc. has to affect climate. It's thermodynamics.
Changing the CO2 in atmosphere, also has to affect climate in a certain way. Whether it's the "climate thermostat" like the alarmists like to say I do not know, but I don't doubt it affects climate in a small or unknown way.
You are correct that human activity, apparently including even CO2 generation, would have an effect on climate. But so would a guy spitting in the ocean--one guy only, one time only.
No engineer I have ever known personally would be concerned at all about the idea that the effect of increased man-caused CO2 in the atmosphere would surely have a small but non-zero effect on climate. The key phrase is "small but non-zero." A good engineer would rework that phrase to be "non-zero but miniscule."
The matter that you are overlooking is the fact that the anthropogenic effect would be so
miniscule as to be
irrelevant. How do we know that? It is because there are other climatological issues that
are massively important; these
dwarf any CO2 effects. Another way to look at the miniscule character of man-related CO2 effects is to realize that previous CO2 levels were much higher than in our day and without any deleterious effect, climate-wise.
Even if we worry about the "butterfly effect" (an idea that is important in chaos physics), we can ignore the CO2 effect for the reason I presented earlier: there are geophysical matters that completely gobble up the significance of man-caused CO2. Besides, chaos physicists ultimately instruct us that
we cannot stop their kind of chaos anyway.
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Anyway, the whole AGW mess is a political hoax mainly designed to hurt the U.S. economy--which is why the U.N. is behind it. The fact that some credentialed scientists have bought into AGW like stupid cows in a herd based mainly on the phony claims that practically every smart guy embraces the AGW scare--over the strenuous objections of tens of thousands of really thoughtful scientists, I might add--merely underscores how dangerous Global Socialism is for a nation dominated by fools (including even a few moderately-high-IQ fools).
FYI, both the warming and the CO2 increases measured in the 20th century can be accounted for by the sunspot trend seen in the 20th century. But our utterly filthy media never, never points this out. They are part of a massive conspiracy to silence us naysayers for the ostensible good of the world. The suppression of anti-AGW science has been almost unbelievably fierce. You need to wrap your brain around
that.
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All of this mess makes me worry about the nomination of Tillery for Secretary of State--who
overruled Exxon-Mobil's engineers concerning AGW when he became CEO. I frankly doubt that Tillery is super-smart, but he is super-political, and I am afraid that he is smart enough to be politically perverse.
Back to the domestic scene, I also suspect that the Socialists would like to make it a crime to spit in the ocean.