Carbon Isotopes

Earth’s atmosphere is made up of a bunch of gases, primarily nitrogen (~78%), oxygen (~20%), and argon (~1%). The remaining ~1% is largely carbon dioxide (CO₂), water vapour, and a variety of other trace gases, many of which are greenhouse gases¹. Despite their relatively small proportion, CO₂ (and other greenhouse gases) are critical players in terms of our Earth’s energy balance, which refers to the balance between incoming and outgoing radiation (i.e., heat energy). These gases trap the outgoing radiation, effectively reducing Earth’s ability to cool, and thus creating an energy imbalance.

Now, important to note that these gases are not a new thing; they have always been a part of Earth’s atmosphere. Before the Industrial Revolution, atmospheric CO₂ levels were ~300 parts per million (ppm) — a concentration that maintained a relatively stable climate, with Earth’s energy balance in near-equilibrium (i.e., not warming or cooling).

However, here we are in 2025, and at the GAW lab in Alert, we are reading a daily average of 430ppm of CO₂. This is indicative of a large energy imbalance in which we are in a warming event, no surprise there, eh? But where did all of this CO₂ come from? Scientists at the University of Heidelberg have been seeking the answer!

These scientists study the isotopic² composition of atmospheric CO₂ as a way to pinpoint its source. To get a bit more science-y: the carbon that makes up CO₂ can come in one of two³ forms: Carbon-14 (¹⁴C) or Carbon-12 (¹²C). While both are naturally occurring in our atmosphere, ¹²C is the most abundant and stable, meaning it does not decay. Carbon-14, on the other hand, does decay.  Living plants take up both forms of carbon during photosynthesis, but after they die,¹⁴C gradually disappears. Fossil fuels, which are largely ancient plant material, have no remaining ¹⁴C, so when burned, they emit only ¹²C, thereby altering the natural ¹⁴C:¹²C ratio in the atmosphere

By analyzing changes in the ¹⁴C:¹²C ratio, scientists at the University of Heidelberg have provided strong evidence that the rise in atmospheric CO₂ is directly linked to human activities, particularly the burning of fossil fuels.

So what does Alert have to do with it? Our GAW lab has been in partnership with this University since 1987. Since then, biweekly samples have been collected and sent to their lab for analysis. Samples are collected by exposing ambient air to sodium hydroxide (NaOH). This initiates a reaction to form sodium bicarbonate (NaCO₃) and is a means of capturing the ambient CO₂. This reaction takes place in a fun looking instrument known as a Raschig tube (see pic below).