As the world warms, many of its driest regions are expected to become even drier. When this happens, the boundaries of arid regions are expected to creep forward, transforming landscapes and wiping out plant life that can no longer cope. Amid the changes, projections suggest that Earth’s drylands could grow to cover more than 40 percent of the planet’s land surface by the end of the 21st century, according to a new study in Environmental Research Letters. But in a surprising twist, the most prominent contributing factor to climate change, rising carbon dioxide (CO2) levels, may actually be slowing the expansion of Earth’s dry lands, researchers say. Drylands are regions facing severe water scarcity, where rainfall is low relative to potential water loss through plant evaporation and transpiration. While the concept is well established, and scientists generally agree on where the world’s major drylands are located, differences in measurement techniques and climate data mean that global estimates of Earth’s dryland coverage can vary substantially. As the new Urge article points out, there are good reasons to find common ground. Spatial distribution of global drylands and associated climate zones from 1994 to 2023 (a); percentage of each climatic zone (b). (Cai et al., Environmental Research Letters, 2026) “The expansion of dryland climatic conditions into previously wetter regions may aggravate water scarcity, ecosystem degradation and desertification, posing challenges for global sustainable development,” explains a team led by scientists from the Chinese Academy of Forestry. “Given the high ecological vulnerability of drylands, updated assessments of dryland extent and future redistribution are needed to support climate adaptation and sustainable development.” In the study, the researchers used updated climate models to map For the analysis, drylands were defined using a measure called the aridity index (AI), which is equivalent to a region’s precipitation divided by potential evapotranspiration (PET), with areas with an AI less than 0.65 classified as drylands. Researchers project that drylands of varying intensity will increase to cover up to 40.28 percent of Earth’s land during 2071-2100. (Sarabi Ramos/Unsplash)One factor contributing to the variation we see in dryland projections is that rising atmospheric CO2 levels over time affect plant transpiration, with plant pores called stomata partially closing when CO2 levels are high. This means that plants lose less water through transpiration overall, which in turn affects calculations using PET, but the team says it is a factor that many previous studies have not taken into account. “Conventional projections often ignore the effects of CO2 on potential evapotranspiration, which can lead to higher aridity estimates and alter patterns of aridity change hotspots,” the authors write. In their own analysis, the researchers used a CO2-modified PET framework that incorporated historical weather data for 1960-2023 and climate models from the sixth phase of the Coupled Model Intercomparison Project (CMIP6). Arid zones are divided into four subtypes, with the majority of the world’s drylands being semi-arid zones (14.72 percent of the land area according to the team’s estimates), with arid zones, predominantly in Australia and China, accounting for 11.24 percent of the Earth’s land. Subhumid dry zones are extensive in China and Russia (6.35 percent), while Algeria, Libya and Saudi Arabia have hyper-arid zones. Representing 6.27 percent of land cover, researchers project that global drylands will increase to cover between 39.31 and 40.28 percent of the Earth’s land surface between 2071 and 2100, depending on the greenhouse gas emissions scenario used, with hyper-arid areas showing the largest increase. CO2 used by the researchers put their numbers significantly below other estimates: A study from a decade ago suggested that drylands could cover up to 56 percent of the Earth’s land surface by 2100. It amounts to a land grab the size of Algeria, or about 30 percent of Australia. Speaking of Australia, while the world’s driest inhabited continent could be the last refuge in a future calamity, it doesn’t fare well in dryland projections. Researchers predict Australia will face the most pronounced changes in drylands this century, followed by Brazil, while parts of Africa are also expected to see widespread changes. The findings are reported in Environmental Research Letters. This article was fact-checked by Rachel Garner and edited by Rebecca Dyer.
