World Climate Declaration: Exhaled Carbon Dioxide Promotes Plant Development

The British Naturalist Alfred Russel Wallace (1823–1913), who was born 200 years ago, argued in a popular book of 1903 that carbon dioxide (CO2) is enriched in exhaled air of humans, and bad for our health, but essential to plant development. With reference to the 2023 World Climate Declaration, we document that exhaled CO2 drastically promotes the growth of a representative land pant. Using regenerated cuttings of Tradescantia geniculata, raised in moist soil, we show that, within 21 days of growth in a day-/night-cycle, CO2-enrichment (ca. 4 vol. % vs. 0.04 vol. % in the control) exerts the following effects: Average stem length is doubled, a three-fold enhancement in the number of branches occurs, and adventitious roots, plus flowers, develop. This CO2-fertilisation-experiment is discussed in the light of the “Global Greening”-phenomenon, documented as large increase in plant biomass since ca. 1850. We also address negative effects of further rising CO2-levels in the atmosphere on the global environment in the ongoing Anthropocene. Finally, we point out that A. R. Wallace was not only a theorizing explorer of nature, but also an expert in animal- and plant physiology.