Climate models reveal how human activity may be locking the Southwest into permanent drought
Pedro DiNezio, University of Colorado Boulder and Timothy Shanahan, The University of Texas at Austin A new wave of climate research is sounding a stark warning: Human activity may be driving drought more intensely – and more directly – than previously understood. The southwestern United States has been in a historic megadrought for much of the past two decades, with its reservoirs including lakes Mead and Powell dipping to record lows and legal disputes erupting over rights to use water from the Colorado River. This drought has been linked to the Pacific Decadal Oscillation, a climate pattern that swings between wet and dry phases every few decades. Since a phase change in the early 2000s, the region has endured a dry spell of epic proportions. The PDO was thought to be a natural phenomenon, governed by unpredictable natural ocean and atmosphere fluctuations. But new research published in the journal Nature suggests that’s no longer the case. Working with hundreds of climate model simulations, our team of atmosphere, earth and ocean scientists found that the PDO is now being strongly influenced by human factors and has been since the 1950s. It should have oscillated to a wetter phase by now, but instead it has been stuck. Our results suggest that drought could become the new normal for the region unless human-driven warming is halted.
The science of a drying world
For decades, scientists have relied on a basic physical principle to predict rainfall trends: Warmer air holds more moisture. In a warming world, this means wet areas are likely to get wetter, while dry regions become drier. In dry areas, as temperatures rise, more moisture is pulled from soils and transported away from these arid regions, intensifying droughts. While most climate models simulate this general pattern, they often underestimate its full extent, particularly over land areas.Arizona Game and Fish Department workers pump water into a wildlife water catchment south of Tucson in July 2023. In normal years, the catchment receives enough rainwater, but years of drought have changed that.Andrew Caballero-Reynolds/AFP via Getty Images Yet countries are already experiencing drought emerging as one of the most immediate and severe consequences of climate change. Understanding what’s ahead is essential, to know how long these droughts will last and because severe droughts can have sweeping affects on ecosystems, economies and global food security.
Human fingerprints on megadroughts
Simulating rainfall is one of the greatest challenges in climate science. It depends on a complex interplay between large-scale wind patterns and small-scale processes such as cloud formation. Until recently, climate models have not offered a clear picture of how rainfall patterns are likely to change in the near future as greenhouse gas emissions from vehicles, power plants and industries continue to heat up the planet. The models can diverge sharply in where, when and how precipitation will change. Even forecasts that average the results of several models differ when it comes to changes in rainfall patterns. The techniques we deployed are helping to sharpen that picture for North America and across the tropics. We looked back at the pattern of PDO phase changes over the past century using an exceptionally large ensemble of climate simulations. The massive number of simulations, more than 500, allowed us to isolate the human influences. This showed that the shifts in the PDO were driven by an interplay of increasing warming from greenhouse gas emissions and cooling from sun-blocking particles called aerosols that are associated with industrial pollution. From the 1950s through the 1980s, we found that increasing aerosol emissions from rapid industrialization following World War II drove a positive trend in the PDO, making the Southwest rainier and less parched. After the 1980s, we found that the combination of a sharp rise in greenhouse gas emissions from industries, power plants and vehicles and a reduction in aerosols as countries cleaned up their air pollution shifted the PDO into the negative, drought-generating trend that continues today. This finding represents a paradigm shift in our scientific understanding of the PDO and a warning for the future. The current negative phase can no longer be seen as just a roll of the climate dice – it has been loaded by humans. Our conclusion that global warming can drive the PDO into its negative, drought-inducing phase is also supported by geological records of past megadroughts. Around 6,000 years ago, during a period of high temperatures, evidence shows the emergence of a similar temperature pattern in the North Pacific and widespread drought across the Southwest.
Tropical drought risks underestimated
The past is also providing clues to future rainfall changes in the tropics and the risk of droughts in locations such as the Amazon. One particularly instructive example comes from approximately 17,000 years ago. Geological evidence shows that there was a period of widespread rainfall shifts across the tropics coinciding with a major slowdown of ocean currents in the Atlantic. These ocean currents, which play a crucial role in regulating global climate, naturally weakened or partially collapsed then, and they are expected to slow further this century at the current pace of global warming. A recent study of that period, using computer models to analyze geologic evidence of earth’s climate history, found much stronger drying in the Amazon basin than previously understood. It also shows similar patterns of aridification in Central America, West Africa and Indonesia. The results suggest that rainfall could decline precipitously again. Even a modest slowdown of a major Atlantic Ocean current could dry out rainforests, threaten vulnerable ecosystems and upend livelihoods across the tropics.
What comes next
Drought is a growing problem, increasingly driven by human influence. Confronting it will require rethinking water management, agricultural policy and adaptation strategies. Doing that well depends on predicting drought with far greater confidence. Climate research shows that better predictions are possible by using computer models in new ways and rigorously validating their performance against evidence from past climate shifts. The picture that emerges is sobering, revealing a much higher risk of drought across the world. Pedro DiNezio, Associate Professor of Atmospheric and Ocean Sciences, University of Colorado Boulder and Timothy Shanahan, Associate Professor of Geological Science, The University of Texas at Austin This article is republished from The Conversation under a Creative Commons license. Read the original article.
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2025 was hotter than it should have been – 5 influences and a dirty surprise offer clues to what’s ahead
The past three years recorded unprecedented global heat, with 2025 being particularly warm. Factors such as greenhouse gas emissions and a decline in solar activity influenced temperatures and extreme weather patterns.
The past three years have been the world’s hottest on record by far, with 2025 almost tied with 2023 for second place. With that energy came extreme weather, from flash flooding to powerful hurricanes and severe droughts. Yet, by most indicators, the planet should have been cooler in 2025 than it was.
So, what happened, and what does that say about the year ahead?
As an earth and environmental scientist, I study influences that affect global temperatures year to year, such as El Niño, wildfires and solar cycles. Some make Earth hotter. Some make it cooler. And one particularly unhealthy influence has been quietly hiding a large amount of global warming – until now.The past three years have been the warmest on record. The chart compiled by the European Union’s Copernicus Climate Change Service shows the comparison to preindustrial-era temperatures in the second half of the 1800s. C3S/ECMWF
Factors that made 2025 cooler than 2024
The Earth’s climate is the result of many factors that change from year to year. Some that helped make 2025 cooler than 2024 include:
La Niña’s arrival: La Niña is part of the El Niño-Southern Oscillation, a natural climate pattern that fluctuates between warm El Niño conditions and cooler La Niña conditions. During El Niño, the Pacific Ocean heats up along the equator, influencing the atmosphere in ways that can cause intense storms, droughts and heat waves around the planet. La Niña does the opposite; it’s like putting an ice pack on the atmosphere.
Both 2023 and 2024 were El Niño years, but in 2025 conditions shifted to neutral and then to La Niña starting in September.
The solar cycle: The Sun reached its solar maximum near the end of 2024, the peak of its energy output in an approximately 11-year cycle, and began declining in 2025. So, while the sun’s output was still stronger than average in 2025, it was less than in 2024.
Fewer wildfires: Despite some destructive blazes, the world also saw fewer wildfires during 2025 than 2024, which put less carbon dioxide – a planet-warming greenhouse gas – into the atmosphere.Major warming and cooling influences from 2016 to 2025. Each graph starts at 2016. Anthropogenic warming, natural carbon sinks and sulfur dioxide (SO2) reductions start from zero in 2016 to illustrate cumulative changes to existing reservoirs; El Niño/La Niña and the solar cycle show real-time influences on the global temperature, relative to mean values. Michael Wysession. Data: Global Carbon Project (Anthropogenic Global Warming, Natural Carbon Sinks); NOAA (El Niño/La Niña, Solar Cycle); SO2 Reductions (FaIR Analysis by Carbon Brief)
Several other factors made 2025 warmer than expected, and some are likely to continue to increase in 2026. They include:
Greenhouse gas emissions: The big driver of global warming is excess greenhouse gas emissions, largely from burning fossil fuels, and 2025 had plenty.
Greenhouse gases trap heat near Earth’s surface like a blanket, raising the temperature. They also linger in the atmosphere for years to centuries, meaning gases released today will continue to warm the planet well into the future. The levels of carbon dioxide, methane and nitrous oxide in the atmosphere all increased in 2025.
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Sources of worldwide carbon dioxide emissions that have grown the most in recent decades. Carbon Brief, CC BY
Earth’s energy imbalance: Other sources can disrupt the natural balance between the amount of sunlight that reaches Earth and the lesser amount radiated back to space. A recent study found that Earth’s energy uptake surged and temperatures rose quickly when a rare three-year La Niña in 2020-2022 shifted to El Niño in 2023-2024.
Declining polar ice, which efficiently reflects sunlight back into space, also affects the energy balance. As sea ice declines, it leaves dark ocean water that absorbs most of the sunlight that reaches it. In a spiraling feedback, warmer water melts sea ice, allowing more sunlight into the ocean, warming it faster; 2025 had the lowest winter peak of Arctic sea ice on record and the third-lowest minimum extent of Antarctic ice.
Air pollution: Sulfate aerosol pollution from coal combustion and burning heavy fuel oil in shipping has also been affecting Earth’s energy balance. It has been masking the full effects of human-caused greenhouse gases for years by reflecting sunlight back into space, creating a cooling effect. But sulfate aerosol pollution is also a serious health hazard, blamed for about 8 million human deaths per year from lung diseases.
Recent reductions in sulfate pollution – now 40% less than 20 years ago – have meant about a 0.2 F (0.13 C) increase in global temperatures. Much of the reduction was from China’s efforts to reduce its notoriously bad air pollution in recent years and international shipping rules in effect since 2020 that have reduced sulfur emissions from large ships by 85%.Sea ice levels were near record lows for both Arctic and Antarctic ice in 2025. Carbon Brief, CC BY
Taking all factors together, humans are now warming the planet at a faster rate than at any point in human history: at about 0.5 F (0.27 C) per decade. That extra heat can fuel extreme weather, including flash floods, heat waves, extended droughts, wildfires and coastal flooding, affecting human lives and economies.
Predictions for 2026
Most climate models predict 2026 will be about as hot as 2025, depending on whether a Pacific El Niño develops, which forecasters give about a 60% chance of happening. The planet is already starting the year out warm, even if it doesn’t feel like that everywhere. While January was very cold in parts of the U.S., globally, Earth saw its fifth-warmest January on record, and much of the western U.S. saw one of its warmest winters on record.
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A severe winter storm that brought crippling freezing rain, sleet and snow to a large part of the U.S. in late January 2026 left a mess in states from New Mexico to New England. Hundreds of thousands of people lost power across the South as ice pulled down tree branches and power lines, more than a foot of snow fell in parts of the Midwest and Northeast, and many states faced bitter cold that was expected to linger for days.
The sudden blast may have come as a shock to many Americans after a mostly mild start to winter, but that warmth may have partly contributed to the ferocity of the storm.
As atmospheric and climate scientists, we conduct research that aims to improve understanding of extreme weather, including what makes it more or less likely to occur and how climate change might or might not play a role.
To understand what Americans are experiencing with this winter blast, we need to look more than 20 miles above the surface of Earth, to the stratospheric polar vortex.On the morning of Jan. 26, 2026, the freezing line, shown in white, reached far into Texas. The light band with arrows indicates the jet stream, and the dark band indicates the stratospheric polar vortex. The jet stream is shown at about 3.5 miles above the surface, a typical height for tracking storm systems. The polar vortex is approximately 20 miles above the surface. Mathew Barlow, CC BY
What creates a severe winter storm like this?
Multiple weather factors have to come together to produce such a large and severe storm.
Winter storms typically develop where there are sharp temperature contrasts near the surface and a southward dip in the jet stream, the narrow band of fast-moving air that steers weather systems. If there is a substantial source of moisture, the storms can produce heavy rain or snow.
In late January, a strong Arctic air mass from the north was creating the temperature contrast with warmer air from the south. Multiple disturbances within the jet stream were acting together to create favorable conditions for precipitation, and the storm system was able to pull moisture from the very warm Gulf of Mexico.The National Weather Service issued severe storm warnings (pink) on Jan. 24, 2026, for a large swath of the U.S. that could see sleet and heavy snow over the following days, along with ice storm warnings (dark purple) in several states and extreme cold warnings (dark blue). National Weather Service
Where does the polar vortex come in?
The fastest winds of the jet stream occur just below the top of the troposphere, which is the lowest level of the atmosphere and ends about seven miles above Earth’s surface. Weather systems are capped at the top of the troposphere, because the atmosphere above it becomes very stable.
The stratosphere is the next layer up, from about seven miles to about 30 miles. While the stratosphere extends high above weather systems, it can still interact with them through atmospheric waves that move up and down in the atmosphere. These waves are similar to the waves in the jet stream that cause it to dip southward, but they move vertically instead of horizontally.A chart shows how temperatures in the lower layers of the atmosphere change between the troposphere and stratosphere. Miles are on the right, kilometers on the left. NOAA
You’ve probably heard the term “polar vortex” used when an area of cold Arctic air moves far enough southward to influence the United States. That term describes air circulating around the pole, but it can refer to two different circulations, one in the troposphere and one in the stratosphere.
The Northern Hemisphere stratospheric polar vortex is a belt of fast-moving air circulating around the North Pole. It is like a second jet stream, high above the one you may be familiar with from weather graphics, and usually less wavy and closer to the pole.
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Sometimes the stratospheric polar vortex can stretch southward over the United States. When that happens, it creates ideal conditions for the up-and-down movement of waves that connect the stratosphere with severe winter weather at the surface.A stretched stratospheric polar vortex reflects upward waves back down, left, which affects the jet stream and surface weather, right. Mathew Barlow and Judah Cohen, CC BY
The forecast for the January storm showed a close overlap between the southward stretch of the stratospheric polar vortex and the jet stream over the U.S., indicating perfect conditions for cold and snow.
This is what was happening in late January 2026 in the central and eastern U.S.
If the climate is warming, why are we still getting severe winter storms?
Earth is unequivocally warming as human activities release greenhouse gas emissions that trap heat in the atmosphere, and snow amounts are decreasing overall. But that does not mean severe winter weather will never happen again.
One factor may be increasing disruptions to the stratospheric polar vortex, which appear to be linked to the rapid warming of the Arctic with climate change.The polar vortex is a strong band of winds in the stratosphere, normally ringing the North Pole. When it weakens, it can split. The polar jet stream can mirror this upheaval, becoming weaker or wavy. At the surface, cold air is pushed southward in some locations. NOAA
Additionally, a warmer ocean leads to more evaporation, and because a warmer atmosphere can hold more moisture, that means more moisture is available for storms. The process of moisture condensing into rain or snow produces energy for storms as well. However, warming can also reduce the strength of storms by reducing temperature contrasts.
A warmer environment also increases the likelihood that precipitation that would have fallen as snow in previous winters may now be more likely to fall as sleet and freezing rain.
There are still many questions
Scientists are constantly improving the ability to predict and respond to these severe weather events, but there are many questions still to answer.
Much of the data and research in the field relies on a foundation of work by federal employees, including government labs like the National Center for Atmospheric Research, known as NCAR, which has been targeted by the Trump administration for funding cuts. These scientists help develop the crucial models, measuring instruments and data that scientists and forecasters everywhere depend on.
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This article, originally published Jan. 24, 2026, has been updated with details from the weekend storm.
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A gustnado east of Limon, Colorado. Image Credit: Jessica Kortekaas
Severe weather can produce dramatic sights—but not every spinning column of air is a tornado.
A [gustnado](chatgpt://generic-entity?number=0) is a brief, ground-level swirl of rotating air that forms along a thunderstorm’s gust front. Gustnadoes often appear suddenly, kicking up dust or debris, which can make them look more dangerous than they actually are.
Unlike tornadoes, gustnadoes do not connect to a storm’s rotating updraft. Because of this, they are usually weaker, short-lived, and difficult to detect on weather radar.
Gustnadoes typically last only seconds to a few minutes and are most commonly spotted in dry regions, where loose soil makes their rotation visible.
The takeaway: If it’s spinning near the ground ahead of a storm, it may look intense—but it’s not always a tornado.
Further Reading
Learn the differences between tornadoes, dust devils, and other rotating weather phenomena in our STM Daily News Knowledge Series.
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