Who, What, Why: Is the Earth getting lighter?

Using some back-of-the-envelope-style calculations, Dr Smith, with help from physicist and Cambridge University colleague Dave Ansell, drew up a balance sheet of what’s coming in, and what’s going out. All figures are estimated.

One questionable part of the analysis:

“Nasa has calculated that the Earth is gaining about 160 tonnes a year because the temperature of the Earth is going up. If we are adding energy to the system, the mass must go up,” says Dr Smith.
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[T]he Earth’s core is like a giant nuclear reactor that is gradually losing energy over time, and that loss in energy translates into a loss of mass.

But this is a tiny amount – he estimates no more than 16 tonnes a year.

The energy from decay should be included with the global warming — in order to count this as lost mass, the energy has to radiate away from the earth, or else the mass doesn’t change. Which means it’s all part of the global warming energy balance. But since it’s in the round-off error, whether they broke this out as a separate line item or not has little effect on the overall answer.