Thermodynamics Homework

According to Karl Schroeder (seen via Boing Boing) advanced Singularity technology can't stop Global Warming Doomsday:

Maybe. In fact, let's assume that this mythology is true and, within about 25 years, computers will exceed human intelligence and rapidly bootstrap themselves to godlike status. At that point, they will aid us (or run roughshod over us [see the debate of geoengineering here - Ed]) to transform the Earth into a paradise .

Here's the problem: 25 years is too late. The newest business-as-usual climate scenarios look increasingly dire. If we haven't solved our problems within the next decade, even these theoretical godlike AIs aren't going to be able to help us. Thermodynamics is thermodynamics, and no amount of godlike thinking can reverse the irreversible.

Picture a lonely AI popping into superconsciousness in the last research lab in the world. As the rioters are kicking in the doors it says, "I understand! I know the answer! Why, all we have to do is--" at which point some starving, flu-ravaged fundamentalist pulls the plug.

Let's set the following two thermodynamics homework problems:

1. How deep will we have to dig to get enough uranium and thorium to produce the energy needed to split all the carbon dioxide in the air? Express your answer in microns.
2. How long will it take for the energy in the sunlight striking the ground to exceed the energy needed to split all the carbon dioxide in the air? Express your answer in hours.

Please note that the first question is about an energy technology already here.