How can a small proportion of carbon dioxide in the atmosphere have such a large effect on our climate?

The current (2023) level of CO2 in the atmosphere is about 420 PPM – that is 420 parts of CO2 (by volume) for every million parts of the atmosphere.

That appears really small, doesn’t it? In terms of percentage, it is just 0.04%!

But it is this small proportion and increases to it that are resulting in large climatic changes.

Instances of small climatic changes leading to significant results on earth abound. For example, the ice ages during the last several million years and the warmer periods in between–appear to have been triggered by no more than minor differences in seasonal and latitudinal distribution of the solar energy absorbed by the Earth.

Similarly, geologic records show that the differences in ice cover, sea level and precipitation as well as in plant and animal populations were quite dramatic between the ice ages and the warm interglacials. Yet the global average temperature differences corresponding to these radically different climates were only about 5 degrees C in the tropics and 8 degrees C in polar regions.

Still, if CO2 currently makes up only 0.042% of the atmosphere, it is a bit difficult to believe that such trace amounts can cause such large damages, isn’t it?

But it should not surprise us, because we see even in our normal lives how small amounts of some things can lead to highly magnified results.

Consider arsenic. A small amount of arsenic is enough to kill an entire village!

So, saying that CO2 is “only a trace gas” is like saying that arsenic is only a trace water contaminant.

Essentially, it is not the quantity alone that matters, it is the potent of the substance that matters too. In this case, the potential for CO2 as a greenhouse gas is so high even the trace amounts are enough to make a big difference to global warming.