The answer to that is likely yes. To create man-made fog that would cover a square mile of ocean would take about 40 gallons of seawater and less than $1 in energy. Fog can keep the ocean beneath it cooler during the day by reflecting sunlight then burn off and let the ocean radiate heat at night. This web page about cloud water content is interesting: www-das.uwyo.edu
Clouds can also be used as a blanket to keep the ocean warmer at night if wanted. We can increase clouds over the oceans by increasing the availability of condensation nuclei. The salt in seawater can be used to do that. Man-made clouds and snow are likely powerful tools for active climate management. A passive method such as CO2 reduction is probably one of the more inefficient methods.
I'll take your word for it that man-made fog can be created in this way, at this price. I'll take your word for it that this would cool the ocean underneath the fog. (I'm not sure about this. For one thing, water vapor is a greenhouse gas. For another thing, it was my impression that the effects of cloud formation on the greenhouse effect were not well understood.)
My question 4. remains as to whether this action would influence the effects of climate change positively. Even if you prove you've got an easy "cooling" method there are still some missing steps when it comes to proving you've affected the climate positively. At best, if I buy what you're saying, you've essentially created a local heat-sink out in the middle of the ocean somewhere. But climate is a complex system, it's not as easy as "reduce the temperature somewhere". Would your fog-machine really help in the straightforward, linear way you imply, or might it somehow create a feedback of some sort that would negate or even outweigh the local cooling? What would be the effect on weather, on currents? What amount of energy are you talking about reflecting with your method - is it significant, or a drop in the bucket?
And as a starting matter, we haven't even answered my question 3. - is the predicted climate change (global warming) net-bad or net-good for humanity? Even if your method here would work, if global warming is a net-good, then you're harming, not helping.
Anyway, though, you do suggest an interesting technique & I'd be interested to learn more, got a link? (=a link about man-made fog and how/why it would reduce the greenhouse effect)
Clouds can also be used as a blanket to keep the ocean warmer at night if wanted. We can increase clouds over the oceans by increasing the availability of condensation nuclei. The salt in seawater can be used to do that. Man-made clouds and snow are likely powerful tools for active climate management.
Again, it was my impression (when I actually worked on climate models, in a former life :) that neither cloud-formation nor what their overall effect was (net reflector, because they're "white"? or do they trap heat, because it's water?) were well understood (or modeled). Maybe things have changed since then (it was probably 10 years ago after all).
That's one square mile. There are 224,393,542 square miles of water surface on the planet. How much would have to be covered to result in a significant change in water temp? Just 5 percent coverage would require 11.2 million gallons of water and several million dollars worth of energy. One percent would require approximately 2.2 million gallons of water. And even if this could be done, would it be a lasting effect? How long would the fog have to cover the water? Could the fog last long enough to affect the desired change? I doubt that this would be feasible let alone practical.