The relative number here might be more useful as long as it’s understood that Google already has significant emissions. It’s also sufficient to convey that they’re headed in the wrong direction relative to their goal of net zero. A number like 14.3 million tCO₂e isn’t as clear IMO.
Proof of work, which becomes computationally expensive to scale, along with other heuristics based on your browser and page interaction. I believe it’s less about clicking the box and what happens after you’ve clicked the box.