Several hundred years in the future, technology has significantly advanced to the point where we can far more efficiently extract energy out of the natural world we live in. As a result, energy has become far cheaper, and completely renewable, significantly boosting the economy and sparking innovation. Quality of life jumps up, and with our new money, we move a lot of our focus on climate to focus on philanthropy. Using our new energy, we have drastically improved most third-world countries, westernizing them and almost entirely eradicating poverty.
Another side-effect of this new energy is that climate change has become a thing of the past. It has been replaced by climate-control. We can't change the world temperature overnight, but we can safely and accurately change the temperature by a couple of degrees Celsius per year, with practically no limit on how much we change it (other than, of course, humans have to survive to continue to change it). In comparison, we have very little control over the weather, but we do have some.
Everything in the world is better. There is only one downside. Overpopulation. The economy is great, standard of living is great, no energy crisis, but we are running out of land for the people to live in. We also need more room for agriculture. Space colonization is out the window, as our space travelling abilities have not progressed very much since modern day. However, we have another weapon: Terra-forming the earth. 70% of the surface of the earth is water. If we can bring that number down, we will have more room. How do we go about this?
When the idea first came to me, I thought "Bring the temperature up! That way, more water will evaporate, the ocean levels will fall, and previously underwater land will become beach, previously beach will become habitable land!" I immediately realized that this is a terrible idea. This would
Melt the poles and bring the water level up,
Destroy a lot of agriculture,
Make a lot of desert areas uninhabitable,
Make humans pretty grumpy
and probably a million other things that I can't think of at the moment.
Then I thought "Let's bring the temperature down! More water will freeze, growing the poles and lowering the ocean levels! If we're lucky, some of the poles might even become habitable!" Again, this is a terrible idea, causing
Destroying agriculture with snow, rather than heat,
Increase condensing of water vapor, possibly increasing the water level?
Potentially cause a new ice-age
Again, most humans would be pretty grumpy about the cold.
Then on the extreme ends of the spectrum "Freeze all the water, humans could live on the ice!" (probably a bad idea) or "Melt all the water, humans could live in the desert that used to be the ocean floor!" (Very clearly a terrible idea)
So here's my question: How bad are all of these ideas? I could be totally off, as I am not really a scientist. Assuming the technology exists, can earth pull off any of these? Is there any practical amount of climate change that could improve the world and make more land?