“The radiative forcing of the CO2 we have already put in the atmosphere in the last century is … the equivalent in energy terms to almost half a billion Hiroshima bombs each year.”
“Radiative forcing” is the degree to which Earth is warmed by energy produced by the sun and trapped by our atmosphere. So if there were no warming going on due to gases in the atmosphere, primarily carbon dioxide, we’d have to set off almost half a billion Hiroshima bombs a year (1.3 million a day) to get an amount of warming equivalent to what’s happening now.
Here’s a new video from NASA showing what all that warming looks like when dissipated across the entire surface of the planet. (Keep in mind that most of that heat energy is trapped deep in the oceans, which this visualization doesn’t show.)