

A balloon full of helium has more mass than a balloon without helium, but less weight
That’s not true. A balloon full of helium has more mass and more weight than a balloon without helium. Weight is dependent only on the mass of the balloon+helium and the mass of the planet (Earth).
The balloon full of helium displaces way more air than the balloon without helium since it is inflated. The volume of displaced air of the inflated balloon has more weight than the combined weight of the balloon and helium within, so it floats due to buoyancy from the atmosphere. Its weight is the same regardless of the medium it’s in, but the net forces experienced by it are not.
Waste decomposition is part of the natural carbon cycle. Burning fossil fuels isn’t. We should not be suppressing part of the natural cycle so we can supplant it with our own processes. This is Hollywood accounting applied to carbon emissions, and it’s not going to solve anything.