·
·
Wednesday, 9 September 2026dailybeirut.com
Culture & Society
A new study in Environmental Research Letters finds rising atmospheric CO₂ could partially offset desert expansion, with drylands projected to cover 39.31–40.28% of Earth’s landmass by 2100—up from 38.58% in 1994–2023.
Global drylands—areas where water loss through evaporation and plant transpiration exceeds rainfall—are expected to expand significantly this century as global temperatures rise. Under current trajectories, they could cover between 39.31% and 40.28% of Earth’s land surface (excluding Antarctica) by 2100, according to a study published in *Environmental Research Letters*.
Drylands are classified using the Aridity Index (AI), calculated as the ratio of annual precipitation to potential evapotranspiration (PET). Regions with an AI below 0.65 are designated as drylands. However, estimates of their global extent have varied widely due to differences in PET calculation methods and climate data inputs.
This study employed updated climate models that explicitly incorporate the physiological effect of elevated atmospheric CO₂ on plant transpiration. When CO₂ concentrations increase, plants partially close their stomata—the microscopic pores on leaves—reducing water loss. This lowers PET values compared to models that treat vegetation as passive, a factor omitted in many prior assessments.
The researchers used a revised PET model accounting for CO₂-driven stomatal regulation and integrated observational climate data spanning 1960 to 2023. They also drew on simulations from the Coupled Model Intercomparison Project Phase 6 (CMIP6), a coordinated initiative under the World Climate Research Programme (WCRP) designed to project past, present, and future climate change.
Based on the 1994–2023 reference period, drylands covered 38.58% of global land area. The study further breaks this down into four subtypes: semi-arid lands (14.72%), arid lands—concentrated primarily in Australia and China (11.24%), dry sub-humid lands—in China and Russia (6.35%), and hyper-arid lands—in Algeria, Libya, and Saudi Arabia (6.27%).
Projections for 2071–2100 vary by greenhouse gas emission scenario, ranging from 39.31% to 40.28%. Hyper-arid zones show the largest proportional increase. Even the upper bound—40.28%—represents a net growth of 2.37 million square kilometers relative to the 1994–2023 baseline, equivalent in area to Algeria or roughly 30% of Australia’s landmass.
Australia is projected to experience the most pronounced shifts in dryland coverage this century, followed by Brazil. Significant large-scale transitions are also anticipated across parts of Africa.
While CO₂ remains the primary driver of global warming, this research identifies a counterbalancing biophysical effect: its suppression of plant water loss dampens PET, thereby slowing the rate at which regions cross the AI = 0.65 threshold into dryland classification. As a result, the study’s CO₂-adjusted projections are markedly lower than earlier estimates—such as one from a decade ago suggesting drylands could reach 56% of land area by 2100.
The findings were published in *Environmental Research Letters*. The original reporting was provided by ScienceAlert.
