A new study published in Environmental Research Letters suggests that the way plants respond to rising carbon dioxide (CO₂) levels could slow the spread of drylands, challenging earlier predictions that linked warming directly to the expansion of dry areas. Drylands are regions where rainfall is much lower than the amount of water the atmosphere can pull from the soil and plants, making them especially vulnerable to water shortages, land degradation, and desertification. These areas have long been a focus in climate change discussions due to their sensitivity to environmental shifts. Estimates of how much of the Earth’s land is classified as drylands have varied widely, ranging from about 37% to 47%, depending on the data and methods used. Most of these estimates rely on the aridity index, a measure that compares the amount of precipitation to the maximum amount of water that could evaporate or be transpired by plants if water were abundant. However, the data used to calculate these values often come from earlier studies, many of which relied on climate data from before 2010, a time when global climate conditions have significantly changed. The new study accounted for the fact that plants use less water when CO₂ levels are high, which reduces evapotranspiration. By combining historical climate data with projections from 19 major climate models, researchers were able to provide a more accurate picture of how drylands are currently distributed and how they might change in the future. They examined three different emissions scenarios to identify areas where dryness might increase or decrease. According to the findings, drylands covered 38.58% of the world's land area—excluding Antarctica—between 1994 and 2023, with semi-arid regions making up the largest share. Hyper-arid zones, such as parts of Algeria, Libya, and Saudi Arabia, were also identified. While the overall area of drylands has increased since 1960, the rate of expansion has slowed in recent decades. Looking ahead, the study predicts that even under the most extreme emissions scenario, drylands will cover about 40.28% of the world's land by 2100, an increase of about 2.37 million square kilometers. If the effect of CO₂ on plants is not considered, this number could rise to 42.11%. Under a low-emissions scenario, the projected coverage of drylands would be slightly smaller, around 39.31%. The study also highlights that while some regions, like parts of Australia and northern Africa, may face increasing drought risks, others, such as parts of China, could see more rainfall. The researchers note that although the overall expansion of drylands is expected to be relatively small, the way dry and wet regions are distributed across the globe will change significantly. For example, under the highest emissions scenario, nearly 13% of the Earth’s land could see shifts between dry and wet conditions, with drying-to-wetting transitions being more common. The study also emphasizes that the limited global increase in drylands does not mean that local changes are minor. While the overall share of drylands increases by just 1.7 percentage points, the movement of dryland boundaries affects nearly 15% of the world’s land. The researchers caution that the models used have uncertainties, especially near the edges of drylands, where small changes can shift a region from one classification to another. They also note that the study does not fully account for human activities like irrigation, groundwater use, and land-use changes. Future research may refine predictions by incorporating more detailed models of land-atmosphere interactions and considering how vegetation, soil moisture, and human water use influence dryland dynamics.