The first vascular plants on Earth were small shrub-like vegetation. When trees evolved ~385 million years ago, the CO2 level in the atmosphere did not change much and remained at a far lower levels than previously thought (2000-8000 ppm).

With a new mechanistic proxy calibrated in modern club mosses, we have discovered that the atmospheric CO2 levels 410 – 380 million years ago were far lower than previously thought. The paper is published in Nature Communications.

Press releases from University of Copenhagen, Potsdam Institute for Climate, and University of Nottingham. Independent reports appear in Nature Asia, Nature Earth & Environment Behind the paper,, ForskerZonen, Carlsbergfondet, Ingeniøren, Berlingske, and Globe UCPH.


The emergence of the first progymnosperm forests (Archeopteris trees up to 30 m tall) from a world of only smaller shrub-like vegetation occurred ~385 million years ago. At that time scientists generally agreed that atmospheric CO2 levels were more than 10-times higher than today. With a newly calibrated proxy applicable to modern and ancient vascular plants (lycophytes), we revise this idea and show that the earliest vascular exosystem might have had larger imprint on atmospheric CO2 levels than deep-rooted plants. This illustration was generated in part with GPT-3, OpenAI’s large-scale language-generation model. Upon generating draft language, the author reviewed the illustration to their own liking and takes ultimate responsibility for the content of this illustration.