I posted elsewhere about the waste of time in being a mental flyswatter. But this is a relatively easy one.

So I'm not going to go to the trouble of scratching up the numbers that would show that the amount of raw heat released into the atmosphere by the decay of free-floating radioactive substances is utterly insignificant compared to hundreds of other natural and artificial heat sources that affect the Earth, and that this tiny amount of heat would be as likely to drive off our atmosphere as I would likely to be able to go down to the Alameda Naval Museum pier and capsize the U.S.S. Hornet by bending over and farting at it.

Do some real math, and get some real answers. A free clue: Find out the length of time over which 1 kg of finely dispersed U235 releases 18.7 million kilowatt-hours of energy (assuming your number is accurate) as heat by natural decay.