There are three numbers you need to really understand global warming, 275, 390, and 350.
For all of human history until about 200 years ago, our atmosphere contained 275 parts per million of carbon dioxide. Parts per million is simply a way of measuring the concentration of different gases, and means the ratio of the number of carbon dioxide molecules per million other molecules in the atmosphere. 275 ppm CO2 is a useful amount without some CO2 and other greenhouse gases that trap heat in our atmosphere, our planet would be too cold for humans to inhabit. Continue reading “350 — the most important number in the world”