Fading of the ¹⁴ C bomb peak – students’ project to observe the Suess effect

Abstract The natural variability of atmospheric 14 C has been significantly altered by anthropogenic activities linked to technological advancements and energy consumption over the past two and a half centuries. The Suess effect, a consequence of the combustion of old carbon (fossil fuels) since the mid-18th century and the bomb peak from the mid-20th century’s thermonuclear tests, has obscured the natural 14 C signal in the atmosphere. This study presents a 14 C analysis of leaves, flowers, and grass collected from various locations worldwide. Over the last 10 years, more than 150 samples have been collected and used as materials for experiments conducted by students in physics lab classes (Department of Physics, ETH Zurich) or as part of school projects. Short-lived vegetal fragments are ideal material for teaching radiocarbon dating and demonstrating our research. The collection of data presented here underscores the sensitivity of radiocarbon analysis for detecting fossil carbon components. Trees from urban sites worldwide demonstrate a dilution of the atmospheric 14 C concentration of 2–3%. Trees growing close to busy roads and traffic show a dilution of up to 10%. Moreover, the data show a fading trend of the bomb peak observed from 2015 to the present, as well as the direct impact of fossil CO 2 on the 14 C concentration of the living biota around us.