Scientists have suspected it for some time, but can now confirm that the concentration of helium-4 in the atmosphere is increasing. And that is a direct result of our predilection for fossil fuels.

The atmospheric increase of helium-4 is small, researchers write in the journal Nature Geoscience, but clearly measurable. According to the researchers, the atmospheric concentration of the isotope (see box) has been increasing since 1974 and can be traced back to both the combustion and extraction of fossil fuels.

You are probably familiar with the element helium. This new research focuses on an isotope of this element: helium-4. It is one of two naturally occurring isotopes of helium. Isotopes are atoms of the same chemical element (in this case helium) that have the same number of protons, but the number of neutrons in the atomic nucleus differs. In the case of helium-4, the atomic nucleus consists of two protons and two neutrons. The result is a stable helium isotope that differs from the other naturally occurring helium isotope: helium-3. Helium-3 also has two protons, but only one neutron.


The lion’s share of the amount of helium-4 on Earth is created by radioactive decay processes in the Earth’s crust. The helium-4 that is created in this way then collects in the same reservoirs as fossil fuels (especially natural gas). As soon as people remove that natural gas from the reservoir and burn it, helium-4 is also released. Given our dependence on fossil fuels and the large scale on which we extract and burn them from the earth, it was to be expected that the atmospheric concentration of helium-4 was also rising. But researchers were unable to confirm that. Until now.


American researchers have developed a very precise method to measure the atmospheric concentration of helium-4. They looked at the ratio between helium-4 and dinitrogen. Because the concentration of high-nitrogen in the atmosphere is constant, a change in the ratio between the two elements indicates a change in the amount of helium-4. And so the researchers discovered that the concentration of helium-4 has increased just a little bit.


The presence of helium-4 in the atmosphere has no further effect on the greenhouse effect; the isotope does not contribute to global warming. Nevertheless, it is valuable that researchers are now able to measure and monitor the concentration of helium-4. For example, researchers can use helium-4 – which ends up in the atmosphere during the extraction and combustion of fossil fuels – to get a better picture of the extent to which fossil fuels are used.


In addition, the research also has implications for the helium-3 mentioned above. This isotope is being looked at with above-average interest because it is believed to play a key role in the development of safer nuclear reactors. In these (still hypothetical) nuclear reactors, the isotope could then be fused with an isotope of hydrogen and thus generate energy, without the formation of radioactive waste. However, it has not yet been proven whether helium-3 can really be the solution to our energy and climate problem in this way. And even if researchers can prove this in the long run, we will immediately be faced with a new challenge: helium-3 is very scarce on Earth. At least we thought so. Because the new research cautiously hints that helium-3 is slightly less scarce than we think. For example, the researchers point out that previous studies have shown that the ratio between helium-3 and helium-4 in the atmosphere is always the same. The fact that the amount of helium-4 is now increasing suggests cautiously that the amount of helium-3 must also be increasing. “We don’t know for sure, but I wonder if there’s more helium-3 coming out of the Earth than we previously thought,” said study researcher Benni Birner. “And whether we can perhaps collect that and use it to run our future nuclear reactors.”

And so the research not only confirms previous suspicions, but also raises new questions. For example, about how helium-3 is produced and in what quantities. “The implications are far from clear,” says Ralph Keeling. “It requires more research.”