“Irreversible Rain Chaos” Warning

More than 2 billion people could face chaotic and Irreversible Rain Chaos with permanently disruption of Water availability

Higher global temperatures mean the inter tropical convergence zone could shift south, throwing off precipitation trends for a major swath of humanity, according to new research. Nearly 2 billion people could face wild disruptions in water availability if the planet continues to warm, and the change could be irreversible. Earth's average surface temperature is already about 2.1 degrees Fahrenheit (1.2 degrees Celsius) higher than pre-industrial levels, and with 2024 the hottest year on record, the future forecast is not promising. A looming climate shift could permanently scramble global rainfall patterns, threatening water security for nearly 2 billion people. A new study warns that a projected rise in global temperature may cause an irreversible shift in global rainfall patterns across key equatorial regions. This large-scale disruption centres on the behaviour of the inter tropical convergence zone (ITCZ), a critical atmospheric belt responsible for much of the world’s rainfall near the equator.

The study looked at what would happen should global temperatures swell to 2.7 F (1.5 C), even for just a few decades. Such an increase in global temperature could have a permanent impact on the inter tropical convergence zone (ITCZ), a region near the equator where trade winds from the northern and southern hemispheres meet. "These impacts that we quantify here will be there for the long term," said lead author Norman Steinert, senior climate researcher at the Centre for International Climate Research in Norway. The ITCZ has a heavy influence on rainfall patterns, and the increase in global temperatures could cause it to shift south, changing the length and intensity of wet and dry seasons, especially in parts of Africa, the Amazon and Southeast Asia. Too much rain in some areas and not enough in others could have dire effects on agriculture, ecosystems and water availability for a major portion of the planet. The inter tropical convergence zone (ITCZ) is not just a meteorological curiosity. It’s a colossal band of tropical clouds formed by the meeting of trade winds from both hemispheres, stretching across regions such as Central and West Africa, the Amazon Basin and Southeast Asia. This threshold is perilously close: Earth’s current warming already stands at 1.2°C, with 2024 on track to be the hottest year on record.

Several factors affect this wide band of clouds, including the ocean's largest conveyor belt, a network of currents known as the Atlantic Meridional Overturning Circulation (AMOC). Emerging research suggests this conveyor belt is weakening, largely due to climate change. The researchers looked at two different scenarios run by eight different Earth System Models, powerful climate simulation tools. One "idealized" scenario analysed how precipitation patterns might change if atmospheric CO2 increased at a rate of 1% per year for 140 years, then decreased at the same rate for another 140 years, it's a "clean," way to assess the impact of a rise and fall in global temperatures, if unrealistic, Steinert said. The study’s authors used eight state-of-the-art Earth System Models to simulate both idealized and realistic future climate scenarios. Results show that even temporary warming could push the ITCZ significantly southward, bringing unprecedented changes in wet and dry seasons. Some areas may become deluged, like northeast Brazil, while others, like parts of Africa and Southeast Asia, could see dramatic declines in rainfall. These impacts may become permanent on human timescales.

The researchers also looked at data showing a potentially more realistic scenario, where emissions increase until the year 2040, which is followed by aggressive mitigation efforts to bring the global temperature back down. The assumption is "that we won't be able or won't like to live in a warmer world, and would make actual efforts to bring temperatures down again at some point. Most of the projections resulted in little or no shift in the inter tropical convergence zone. But in one of the idealized scenarios and two of the more realistic scenarios, the zone shifts significantly, causing potentially major upheaval to rain patterns for much of the world. Researchers modelled two major climate trajectories. The first was an “idealized” case where carbon dioxide levels rise 1% annually for 140 years, then fall at the same pace. The second mimics a more likely future: emissions rise until 2040, followed by strong global mitigation efforts. While some scenarios showed minor ITCZ shifts, others pointed to massive disruptions in rainfall zones which would not recover even after cooling begins. The modelling also accounts for the deteriorating state of the Atlantic Meridional Overturning Circulation (AMOC), the ocean’s massive heat transport conveyor. As this weakens, its effect on atmospheric circulation compounds the ITCZ’s instability. But the study highlights a critical risk: delayed effects. Even if global temperatures decline, ocean and atmospheric systems react slowly, leaving the door open to irreversible shifts. As rainfall becomes erratic and regionally imbalanced, the threat to agriculture, freshwater supplies and food security intensifies.

Based on the number of models predicting different outcomes, the paper describes the ITCZ shift as “unlikely.” But given the already weakened response of the AMOC and a time lag between when the climate warms and when the ocean heats up, the researchers argue a shift in the ITCZ may be more likely. The timing and intensity of weather patterns could disrupt the lives of billions, as well as complicate agriculture that relies on consistent weather patterns. In total, 23% of the world population and more than 12% of the global land area could be impacted. “Still, this storyline could play out in the future,” said Richard Allan, professor of climate science at the University of Reading. “Because it has such big possibilities for regional water availability, this has got to be taken seriously.” The study’s most troubling conclusion is that 23% of the global population and over 12% of the Earth’s land surface could experience substantial hydrological disruption. Inhabitants of regions depending on seasonal rainfall for farming, drinking water and hydroelectric energy would face systemic risk. The changes also threaten delicate ecosystems like rainforests and savannas, which rely on predictable seasonal moisture cycles. This is not just a water crisis, it’s a cascade scenario affecting migration, public health, energy supply and global food chains. Once disrupted, these systems are unlikely to revert. “I mean, that’s very clear,” Steinert emphasized. “Cut emissions as soon as possible.”

The likelihood of this scenario playing out is "a low probability, but plausible outcome," Steinert said, and the models suggest the worst impacts would take decades, at a minimum, to play out. In multiple scenarios, the damage was permanent, at least at human-time scales. "It's an important study," Richard Allan, a professor of climate science at the University of Reading in the UK, said. Allan pointed out water availability is more complicated than what the study considered, because the simulations don't take into account the amount of water and moisture in the ground or how much water is flowing in the rivers, for example. While the projected scenarios are not guaranteed outcomes, the risk is no longer negligible. Scientists now characterize these projections as low probability but plausible, meaning they deserve immediate attention and policy response. Delaying action may lock in irreversible outcomes before they’re even visible on the surface. This reinforces a growing body of evidence showing that climate thresholds are not just theoretical, they are real, near, and dangerously unpredictable. If policymakers and the public wait for certainty, it may arrive too late to prevent massive regional destabilization. The clearest course is to slash greenhouse gas emissions now, preventing the Earth from crossing into a new climatic regime with cascading human consequences. In terms of future research, Steinert says it would be helpful to look at the local, specific outcomes for places that might be impacted by shifting weather patterns due to a warming climate. But the best way to avoid these risks is straightforward.