I'm a bright-green environmentalist (meaning that I'm pro-technology, pro-growth, etc. and not a crazy anarcho-primitivist type) that has recently joined the movement promoting nuclear power as the most practical solution to mitigating the worst effects of global warming.
As an environmentalist, I think that global warming is the most serious threat, but we also need to take into account the destruction of land to provide our energy sources. Obviously, coal is terrible on both accounts because it is a heavy carbon emitter and mining techniques such as mountain-top removal are destroying the environment.
The traditional approach for environmentalists has been to promote wind and solar power. Although they are significantly better options than coal, it is probably not possible to replace our entire energy grid with these technologies. The main reason is the intermittent nature of wind and solar that would require large grid energy storage technologies that aren't very mature yet to stabilize the system. The second reason, that I think is often overlooked by environmentalists, is because of the massive amount of land required to meet our electricity demand.
I am selecting three reference plants for comparison. To keep everything fair, I am only using plants currently online and not planned future plants. I attempted to use the largest plants in the world, but that really doesn't matter too much because I am concerned with power/area. If someone finds a plant that is significantly better in power/area than what I cited below (and it would change the implications of what I'm trying to say), please let me know. To make this comparison simpler and make it more favorable towards wind and solar, I am ignoring any issues related to intermittent generation.
The Roscoe Wind Farm in Texas is the the world's largest wind farm. It covers about 100,000 acres and generates 781.5 MW of electricity using 627 wind turbines.
The solar plant in Jumilla, Murcia, Spain is currently the world's largest solar plant. It covers about 100 hectares (247.105381 acres) and generates 23 MW of power with 120,000 solar panels.
Finally, the world's largest nuclear plant is the Kashiwazaki-Kariwa Nuclear Power Plant in Japan. It generates 8,212 MW of power and uses 4.2 km^2 (1,037.8426 acres) of land using 7 Advanced Boiling Water reactors.
If we simply divide power output by land usage, we get the following ratios (which is in MW/acre):
Wind: 0.007815
Solar: 0.093078
Nuclear: 7.912568
This means that wind energy requires 1012 times more land than nuclear energy for the same power output and solar requires 85 times more land than nuclear energy for the same power output.
For example, to build renewable energy with the same power output as the Kashiwazaki-Kariwa Nuclear Power Plant, 1,050,297 acres are needed for wind and 88,217 acres are needed for solar. This is a lot of land that has to be completely dominated by wind turbines or solar panels. Also, keep in mind that all of the material covering this land has to be mined and manufactured, which also has a footprint on the environment.
Finally, let's look at how much land is needed to supply all of the power consumed in the United States (I'm American, so that's what I'm working with). According to Wikipedia, the US consumed 29,000 TWh of energy in 2005 (which is obviously higher now). This number includes everything (transportation, electricity, heating, industrial processes, etc.). I am assuming that a future economy will use electricity for everything (electric cars, heat pumps, etc.) for simplicity. If I divide by the number of hours in a year (8,760), that is about 3.3 TW (or 3,300,000 MW) of power needed. Obviously, this is a bit simplified, but I am just doing this for illustration purposes.
Therefore, to generate all of our energy using current technology, we would need 417,058 acres of nuclear plants (which corresponds to about 402 nuclear plants like the one mentioned above), 35,454,135 acres of solar panels, or 422,264,875 acres of wind turbines. To put things in perspective, we would need to cover all of New York State in solar panels or all of Alaska in wind turbines to generate our 2005 energy usage. We also have to build a grid that can distribute all of that power from places where the wind blows (e.g. the great plains) and the sun shines (e.g. the sun belt) to where it is needed (primarily the Northeast corridor, California, Chicagoland, etc.).
Please also keep in mind that our energy demand is continually rising (which I view as a good thing because more energy = higher standard of living). Solar panels still have lots of room to get more efficient (such as through advanced nanotechnologies) and wind turbines may have some more improvement in efficiency. But I do not think the improvements in efficiency will make the land needs any better.
Overall, going all renewable is pretty much impossible given the massive amount of mining, manufacturing, and land required to do so (as well as dealing with the problem of intermittent generation). Also, using that much land would be incredibly disruptive to the environment. Nuclear power can solve climate change and do it within practical constraints. We should be doing it ASAP.
Finally, if you are going to reply and talk about the disadvantages of nuclear power, please don't waste your breath before you learn all about the Thorium Fuel Cycle, Molten Salt Reactors, and Liquid Fluoride Thorium Reactors (LFTR) in particular. I was once like you and preferred wind and solar over nuclear power because of the risks of nuclear technology. The LFTR technology I cited resolves the vast majority of the problems with nuclear power that you are concerned about (proliferation, nuclear waste, nuclear meltdowns, cost, peak Uranium, and most others) and this technology has been tested since the 60s. Please learn about this.
If you believe I made an arithmetic mistake, a factual error, or a bad assumption, please respond and I will correct it if I agree.
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