The greenhouse gas carbon dioxide (CO₂) is a product of human activities that use carbon-based fuels, such as home heating, cars, and manufacturing plants, to name a few. But CO₂ also has many natural sources, such as soil, volcanoes and all living things that breathe. So a necessary question that should be asked by climate and citizen scientists alike is, “How do you know increases in CO₂ are from human activity?”

There are two ways scientists can measure “human” sources of CO₂ (let’s call this anthropogenic CO₂) and “natural” sources of CO₂ (let’s call this biogenic CO₂). The first uses the radioactive isotope carbon-14 (or ¹⁴C). This is the isotope used in some cases to determine the age of objects (hence the term “radiocarbon dating”), and can also be used to determine the age of CO₂ that is in the atmosphere. How is measuring the age of CO₂ useful in determining what amount of CO₂ is anthropogenic and how much is biogenic? Much of the anthropogenic CO₂ is the result of fossil fuel burning, which, as the name suggests, is really, really, really, old (in the tens to hundreds of millions of years old). But much of the biogenic CO₂ is the result of consumption or decomposition of modern organic matter made by plants and is relatively young (from days to hundreds of years old). So, if you measure the ¹⁴C of CO₂, you can find out how old the CO₂ in the sample is and calculate how much of it is anthropogenic CO₂. The caveats to this approach are that it does not work when wood is the fuel, nor does it work for slash-and-burn farming practices. Also at the current state of technology, this analysis costs about $500 per sample.

An alternative strategy is to measure carbon monoxide (CO). CO is already an important molecule to atmospheric and climate scientists, because it affects levels of other greenhouse gases. But, CO can also be used as a tracer of anthropogenic CO₂. How does this work? In an ideal world, the combustion of fuel would be 100% efficient, which means that when you rev the engine of your car, the exhaust would be exclusively CO₂ and water. However, no combustion is 100% efficient, so a number of other combustion products arise from burning, CO among them. Thus, any time anthropogenic CO₂ is produced, a little bit of CO will always come with it. In other words, if you were to see an increase in both CO₂ and CO, then you know the increase in CO₂ is from anthropogenic sources; but if you were to measure an increase in CO₂ with no change in CO, then the increase is from biogenic sources. And best of all, it works with any source of carbon burning, including wood fuel and slash-and burn farming.

Here at Picarro, we are working together with scientists from the National Aeronautics and Space Administration (NASA), the National Oceanic and Atmospheric Administration (NOAA), the Chinese Meteorological Institute (CMA) and a number of other institutes to trail blaze the precise measurement of both CO₂ and CO at the same time. With this data, scientists will be able to measure exactly how much anthropogenic CO₂ is released to the atmosphere over time, and relate that information to broad climate factors such as temperature and precipitation. This will help scientists shed light on the relationship between human activities and the planet we live on, which in turn will enable a better prediction of future climate scenarios.