Given that those molecules are absorbed at different wavelengths, the machine can measure the amount of absorption and calculate the concentration of greenhouse gases in parts per million.
Most of this is then absorbed by so-called carbon sinks, a mixture of photosynthesising plants and chemical precipitation, while a small amount remains to contribute to the rise in carbon-dioxide concentration that has been going on for the past 150 years.
Although the carbon dioxide in the atmosphere remains at a concentration of 0.03 percent all over the world, the amount in the air has not always been the same.