If you look at the way climatologists describe global warming, you'll see that they use a lot the term "
As we keep emitting CO2 and other gases in the atmosphere, the greenhouse forcing increases, as you see in the figure below (Hansen 2011).
In this figure,
In any case, we are talking about huge numbers, at least hundreds of TW. For comparison, think that the total primary energy generated by burning fossil fuels is "just" about 15 TW, and practically all of it is eventually turned into heat. So, the indirect greenhouse warming effect is 1-2 orders of magnitude larger. We may also compare with the total solar irradiation that arrives to the earth's surface, around 90,000 TW (Szargut 2003). The effect of the sun is much larger than the human forcing, but not so much larger that the latter can be considered negligible. So, it is not surprising that human activities are causing a detectable warming of the whole planet.
Note also that we have been discussing just the effect of the current forcing. But, whereas the heat from burning fossil fuels is rapidly dissipated, CO2 remains in the atmosphere for a long time, tens of thousands of years and even more (Archer 2005). And this CO2 will keep
At this point, we can try to visualize these values by comparing them to something familiar. As an order of magnitude, let's take the number calculated from Zhang and Caldeira's paper, that is a forcing of 800 TW resulting from CO2 alone. That would correspond to 800 billion electric heaters of 1 kW each, all turned on together.
Considering that there are more than seven billion people on the earth, we may think that the CO2 forcing, alone, is equivalent to each one of us turning on a hundred electric heaters of one kW each. The net forcing - the actual heat being added to the atmosphere - is smaller, but the overall picture doesn't change: we can visualize it as corresponding to 250-400 billion heaters, about 50 per person. And, if we want to make the number of heaters proportional to energy consumption, people living in the rich West would be associated with many more. Imagine each home in your neighborhood stacking hundreds of electric heaters in their front yard, all turned on at full power, and you have some idea of what we are doing to our planet.
So, we have turned the heat on, and now we discover that there is no way to turn it off. (At least not as easily as you can turn off an electric heater). The best we can do, for the time being,
h/t Steve Easterbrook, Dana Nuccitelli, John Cook, Ben, Michael Tobis, John Abraham, and others. Note also that there are other attempts to visualize the total amount of heat generated by human forcing, for instance, in terms of "four Hiroshima bombs detonated per second" Spectacular, but probably less intuitive than electric heaters.
Fate of fossil fuel CO 2 in geologic time Journal of Geophysical Research vol. 110 (C9) p. C09S05(2005)
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Zhang, Xiaochun, Caldeira, Ken, (2015) Time scales and ratios of climate forcing due to thermal versus carbon dioxide emissions from fossil fuels, Geophys. Res.