The Earth gets a tremendous amount of energy from the Sun each year, roughly 100,000 quads (quadrillion BTU) if memory serves. All human energy consumption from all sources was about 400 quads according to this source. We're not a closed system. If the sun were to somehow stop shinning, virtually all life on the surface and deep into the oceans would die in fairly short order. Perhaps the only life that would continue to exist would be that around the deep ocean vents.

I've always believed that Buckminster Fuller's "Spaceship Earth" concept, while inspired, was flawed. A more accurate concept would be "Spaceship Solar System" because we not only get energy from the sun, we have the potential to harness tremendous resources from asteroids and other planets.

It isn't just that the gloom and doom crowd hasn't been right yet, they've been proven spectacularily wrong time after time. Why anyone gives them any credibility at all is beyond me.