At a Glance
- Monsoons provide essential seasonal rainfall for billions worldwide, and new research shows that the atmosphere retains a moisture-driven memory that influences monsoon timing and intensity each year.
- Scientists discovered that the atmosphere exhibits bistability, maintaining either a dry or rainy state depending on its past moisture levels, rather than responding instantly to solar radiation changes.
- Using real-world data and high-resolution models, researchers showed that monsoon rainfall switches on or off abruptly when atmospheric moisture crosses a critical threshold.
- This switching behavior, or tipping, is common in climate systems, but monsoons are unique because they tip annually and predictably return to their starting state.
- Disrupting this annual moisture buildup through climate change could drastically alter global rainfall patterns, threatening agriculture and water supplies for large portions of the world’s population.
Monsoons are critical to the livelihood of billions of people, bringing much-needed rainfall to regions like India, Indonesia, Brazil, and China. Scientists have understood monsoon rainfall as a seasonal response to the sun’s changing energy. However, new research reveals that the atmosphere has a “memory” that influences the timing and intensity of monsoon rains. This study, published in Proceedings of the National Academy of Sciences, shows that the atmosphere’s state—whether dry or rainy—depends on its history, particularly the amount of moisture it has accumulated over time.
The research team, led by scientists at the Potsdam Institute for Climate Impact Research (PIK), discovered that the atmosphere can switch between two stable states: a dry state in the winter and a rainy state in the summer. This “bistability” means that even if solar radiation changes, the atmosphere does not always respond immediately. In spring, the atmosphere is typically dry, but it fills with water vapor over time, which kickstarts the monsoon. By autumn, even as solar radiation weakens, the atmosphere can continue to support rainfall due to its accumulated moisture.
The researchers used real-world data from countries like India and China and high-resolution atmospheric models to explore this phenomenon. Their findings showed that the monsoon system behaves like a switch, turning “on” or “off” abruptly, depending on how much water vapor is in the atmosphere. When the moisture level exceeds a certain threshold, rainfall begins. If the moisture falls below this level, the rains stop. This behavior, known as “tipping,” is a characteristic of many climate systems, such as ocean currents or ice sheets, but the monsoon has a special twist: it crosses its tipping point every year and then returns.
The implications of this research are significant. If this natural cycle is disrupted—whether by pollution, global warming, or other factors—it could lead to drastic changes in rainfall patterns, affecting agriculture and water resources for billions. Understanding the tipping points of monsoon systems might help scientists develop early warning systems to predict sudden shifts in rainfall, potentially mitigating future climate-related challenges.
References
- Katzenberger, A., & Levermann, A. (2025). Monsoon hysteresis reveals atmospheric memory. Proceedings of the National Academy of Sciences, 122(19), e2418093122. https://doi.org/10.1073/pnas.2418093122
- Potsdam Institute for Climate Impact Research. (2025, May 7). The atmospheric memory that feeds billions of people: Monsoon rainfall mechanism discovered. Phys.Org; Potsdam Institute for Climate Impact Research. https://phys.org/news/2025-05-atmospheric-memory-billions-people-monsoon.html
