Would dropping large blocks of ice into the ocean mitigate global warming? This amusing Futurama sketch 'solves' global warming by dropping increasingly larger blocks of ice into the ocean. Presumably the blocks of ice are harvested from a different planet.
Would this theoretically be effective?
My understanding is that by global warming, we mean an increased amount of energy in Earth's atmosphere. Adding ice to the planet wouldn't remove energy from the planet, it would just add matter to the planet. However, possibly you could argue that energy is transferred from the atmosphere to the hydrosphere. However, even if that's the case, would that constitute a reduction in global warming?
 A: Well I would mostly dismiss the concern of the type:

Adding ice to the planet wouldn't remove energy from the planet, it would just add matter to the planet.

Sure, it increases the mass of the biosphere, but it would (in a cursory look) also decrease the temperature since the added water is lower energy than the average.

We need an additional first-level qualifier.  I do believe (I'll check the numbers later) that the kinetic energy per unit mass for being in orbit far exceeds the melting heat of water.
This presents a bizarre quandary for people who seriously still want to ask the question.  If you drop it from space, the gravitational energy of the ice will melt it and add even more heat.  That will increase the temperature of the Earth, even initially.
So... we would drop it in slowly?  This would involve something exotic, like a space elevator, but that will suffice as an plot device here.  Ironically, lowering the ice would produce a tremendous amount of energy which could be harvested fairly directly from space elevator pulleys.  So while the ice is intended to cool the Earth, it actually produces far more energy than the energy it subtracts from Earth.  Clearly, using this extra energy on Earth would negate any benefit, but it could be safely used in space.

With those specifiers, we now have ice falling from the sky, but only a responsible altitude which leaves most of it as solid.
This would initially decrease the temperature of Earth.  There is a certain "thermal inertia" time scale over which this applies.  The heatup of the ocean itself is a major thing that delays temperature rise in the world we live in today.
Given enough time, however, the extra water will have an impact on Earth's greenhouse gases.  In current studies, the water vapor positive feedback really accounts for the majority of the temperature rise.  That causes more temperature rise for the addition of 1 unit of heat.  Actually, the same feedback would apply when subtracting 1 unit of heat, so you get a multiplier of 2-3 because of that.  That still doesn't change the temporary nature of the addition.
Regarding greenhouse gases, the critical question is how it would affect the water vapor in the atmosphere long-term.  That would clearly be to make the Earth hotter, since adding more water just sounds like it would increase water vapor concentration.  Come to think of it, this might even negate the initial cooling effect if it was vaporized before hitting the ocean!

There are a myriad of other feedback effects we could consider.  If we compare albedo of different land types, we see that water has an extremely low albedo.
That would indicate that more water will cause the Earth to absorb more direct sunlight.  It's hard for me to say whether this would have a larger or smaller effect than the water vapor increase, although I'm tempted to guess a larger effect.  Anyway, they're both in the same direction.
I'm sure we could find an effect that cools the Earth due to the creeping shorelines.  This is a notoriously complicated science.  However, it looks like almost all long-term signs point to "hotter".
But for the near-term, that just means you have to add more ice at a faster rate.  I doubt it would affect the conclusion by much.  You would add more until flooding the Earth.
A: The issue with greenhouse gases isn't primarily that they are causing temperatures to change — that's part of the reason that people are trying to steer the discussion from "global warming" to "climate change."  The issue is that they change the steady-state solution for the sun-earth-sky thermodynamic system.
We are changing Earth's energy budget, and average temperatures are changing to adjust to the new equilibrium.
To keep the planet cooler than its new equilibrium temperature, you'd have to continually add ice to it, the same way you have to keep adding ice to your drink in the summertime.  This flaw in the plan is alluded to in your clip ("Solving the problem once and for all!" "But–" "Once and for all!").
This is not to mention that bringing cool ice from outside of Earth might well actually increase the total thermal energy on Earth, since dropping the ice from the sky to the surface would release quite a bit of gravitational potential.  An icy meteorite, after all, would still make a big crater.  That calculation is straightforward enough, but I don't think you're asking about it.
That's also not to mention that atmospheric climate change is only one of the dramatic changes taking place in the Anthropocene.  Already the oceans are absorbing some of the extra heat from the atmosphere (some fraction of already-observed sea-level rise is due to thermal expansion of the water).  More importantly, the oceans are absorbing some of the new carbon dioxide from the atmosphere, which increases their acidity.  There are credible calculations that in a few decades the increase in ocean acidity will dissolve much of the limestone and calcium carbonate under the sea — which means the end of coral reefs and shelled mollusks.
A: Only if the ice did not come from Earth, would adding ice cool the planet, insignificantly. After all, how large is the planet compared to the amount of ice you could retrieve from space?
A: This would be even theoretically effective if you keep on adding larger and larger chunks of ice with time.
On our planet,  the oceans absosrb a large amount of heat and then their slow radiations which can not leave the atmosphere and are trapped play a major role in heating up the environment. However the ice sheets up north and down south effectively reflect major amount of heat.
If you add a large block of ice in the ocean,  it would absorb enough heat to melt it down, and then more heat to raise its temperature to surrounding water. It does seem to have lowered the temperature for a while, but this ice has increased the global sea level!
It means more water on the surface,  which in turn would result in much more absorption of heat from sun, so you'll need to add larger piece of ice, soon the whole earth would be covered in water! And it would be absorbing as much heat from the sunlight as possible, as possibly humans would then not be there to add ice, the heating effect would be much more pronounced leading to global warming of a much greater magnitude than before.
So, adding large pieces of ice would not solve global warming, it is an extremely temporary solution. You can see more about global warming in the movie "An Inconvenient Truth"; what I have explained here is my understanding of what had been shown in a part of the movie.
A: I think there is a better answer to the problem.
Instead of dropping ice on the surface, how about pulverizing it and creating a spherical halo around the Earth. Since it is in space, it will remain ice and reflect a portion of the sunlight away from Earth. In effect, a screen of ice to prevent the planet from heating.
