Even if it was an artificial scale invented in the anime, it would be far to impractical to use it. If minus 1,000,020,000,000 was absolute "zero, which is −273 Celsius or -460 Fahrenheit (I don't remember the decimal points, it's 5AM, sue me), then how would they go around using it for normal temperatures? They'd have to come up with some huge ridiculous number just to say it's 90 degrees Fahrenheit today. I mean, let's say 0 degrees in whatever scale they use is freezing point. That'd mean 2,173,956,521 degrees in whatever scale they use is equivalent to 1 degree Fahrenheit. Then if their news was doing the weather forecast, and it was 80 degrees Fahrenheit, then they'd have to say, tomorrow's temperatures will be around 173,916,521,739 degrees! Give or take a couple hundred million!" Too impractical.