Global drylands could expand to cover over 40 percent of Earth’s land area by the end of the 21st century, according to a new study published in Environmental Research Letters. However, researchers from the Chinese Academy of Forestry found that rising carbon dioxide (CO2) levels may actually slow this territorial creep by altering plant transpiration, challenging previous assumptions about climate change and desertification.
Mapping Global Dryland Expansion Through 2100
Earth’s drylands face severe water scarcity, where precipitation remains low relative to potential water loss through evaporation and plant transpiration. According to researchers, these regions covered approximately 38.58 percent of Earth’s total land—excluding Antarctica—during a baseline period spanning 1994 to 2023.
Using updated climate modeling and the Coupled Model Intercomparison Project phase six (CMIP6) data, the team projects that drylands will expand to cover between 39.31 and 40.28 percent of the terrestrial surface between 2071 and 2100. The exact coverage depends heavily on future greenhouse gas emissions scenarios, with hyper-arid zones projected to experience the most significant relative increases.
How Rising Carbon Dioxide Alters Aridity Projections
Projections tracking global aridity often yield starkly different results depending on measurement techniques and inclusion criteria. A decade ago, separate research suggested drylands could consume up to 56 percent of Earth’s land surface by 2100.
The latest analysis keeps estimates lower by factoring in how rising atmospheric CO2 impacts vegetation. As carbon dioxide concentrations climb, pores on plants called stomata partially close, reducing overall water loss through transpiration. Because standard calculations for potential evapotranspiration (PET) frequently omit this biological response, conventional models often overestimate future aridity.
Did You Know? The upper estimate of 40.28 percent dryland coverage by 2100 represents an increase of 2.37 million square kilometers compared to recent baselines—an area roughly equivalent to the size of Algeria, or about 30 percent of Australia.
Regional Vulnerability: Australia and Brazil Face Severe Shifts
Drylands currently divide into four primary sub-types across the globe. Semi-arid zones dominate terrestrial dryland areas at 14.72 percent, followed by arid zones at 11.24 percent, which are predominantly located in Australia and China. Dry sub-humid zones cover 6.35 percent across regions like China and Russia, while hyper-arid zones account for 6.27 percent, spanning countries such as Algeria, Libya, and Saudi Arabia.
Despite Australia housing vast arid expanses currently, the study indicates the continent will face the most pronounced dryland changes this century. Brazil follows closely behind, with widespread shifts also anticipated across parts of Africa, threatening local ecosystems and global sustainable development.
Frequently Asked Questions
What defines a dryland?
Drylands are defined using an aridity index (AI), calculated by dividing a region’s precipitation by potential evapotranspiration. Areas with an AI score below 0.65 are classified as drylands.
Why do CO2 levels slow dryland expansion?
Higher atmospheric CO2 causes plant stomata to partially close, reducing water loss through transpiration. This physiological change alters potential evapotranspiration calculations, yielding lower aridity estimates than conventional models.
Which regions will experience the most change?
Researchers predict that Australia will face the most pronounced dryland transformations this century, followed by Brazil and parts of Africa.
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