The Earth
No, autumn leaves are not changing color later because of climate change
“Have scientists observed any changes in the timing or intensity of leaf color changes?”
Last Updated on May 21, 2024 by Daily News Staff
Fall foliage on the Danforth Campus of Washington University in St. Louis.
It’s that time of year again. The days are getting shorter, and the nights are cooling down. But when will the natural fireworks display of autumn leaves actually begin this year?
Many people believe that climate change is pushing back the start of fall leaf color to later in the year. The general thinking is that the warmer conditions anticipated under climate change will mean that trees can “hang on” to their green, energy-producing leaves longer. But scientists do not actually see this happening across North American forests, according to an expert at Washington University in St. Louis.
“Warmer temperatures in September and October reduce anthocyanin production in leaves, which could mean that fall colors would become less brilliantly red or purple,” said Susanne S. Renner, honorary professor of biology in Arts & Sciences. “This effect is well documented in certain species, such as sugar maple, where experimental cooling of branches increases anthocyanin concentration and color brilliance. If the first frost comes later than it used to, the brilliant foliage will appear later than it used to.
“However, other factors counteract this. Most important is that trees drop their leaves earlier if they have had a very productive spring and summer. This overrides any delaying effects of a warm fall.
“The end result is that leaves still start to die after about the same amount of time on the tree as they have in years and even decades past,” she said.
In fact, under some scenarios we might even see leaves turning red and yellow earlier. Renner co-authored a 2020 study in the journal Science that showed that increased growing-season productivity drives earlier autumn leaf senescence — the process through which plants break down and reabsorb key nutrients that had been deployed in leaves — in temperate trees.
“If climate warming continues unabated, the situation is likely to change after about 2040, with senescence then starting earlier than it does now,” Renner said.
Here, Renner answers a few additional questions related to autumn leaf color change.
How do temperature and moisture conditions affect leaf color?
Yellow color in fall leaves is due to the retention of carotenoid pigments (xanthophylls) in senescing chloroplasts. Red and purplish color is due to the accumulation of anthocyanins in vacuoles, starting around September.
Rain does not affect these basic processes. Cold temperatures, however, enhance anthocyanin production, as shown experimentally in sugar maple. One can observe this in the sugar maple trees along St. Louis streets, which start turning colors at the very top, where the microclimate is coldest.
How might climate change alter color dynamics?
Because climate warming has resulted in warmer falls, in Canada and North America we are seeing less brilliant fall colors. Color brilliance is hard to quantify, but the effect has been experimentally demonstrated in sugar maple trees.
An interesting confounding factor is cleaner air. Thus, in Europe, atmospheric brightening due to cleaner air since 1983 has led to higher plant photosynthesis in the spring and summer — and earlier leaf senescence (compared with 1950-1982). These data, however, concern the breakdown of chlorophyll, not the production of red or yellow colors.
Will all kinds of trees respond in the same ways?
Absolutely not. Experimental work is revealing great species-specific differences. For example, trees that have nitrogen-fixing symbionts never turn red or yellow. Both pigments help protect leaves against damage from sunlight that is no longer usable for photosynthesis because of the massive degradation of chloroplast proteins in aging leaves. Trees with steady access to nitrogen may not bother with costly anthocyanin, but instead simply drop their leaves while still relatively green.
Are scientists already seeing changes to the timing or intensity of leaf color changes?
Warmer falls reduce the brilliance of red and yellow leaf colors, but brilliance is hard to quantify in long time series for many species. Also, many species simply do not turn red or yellow.
We have a paper under review that analyzes satellite data on “greenness” in Northern Hemisphere forests. We found that across a large majority of forest areas, higher spring and summer temperatures have led to an earlier (!!!) senescence by, on average, about 1.5 days per degree Celsius. Senescence here refers to degradation of chlorophyll or greenness.
Where in the world are autumn leaves most likely to be affected by climate change?
Species that change leaf color to red or yellow are much more frequent in North America than in Europe. With continued climate warming and lack of frost nights in October, colors will be less brilliant, but the onset or dates of color change will not change much because of the counteracting factors that I mentioned earlier. In the more distant future (after about 2040), and with unmitigated climate change, leaf senescence in Northern Hemisphere trees and shrubs will occur ever earlier.
Source: Washington University in St. Louis
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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.
Michael Wysession, Washington University in St. Louis
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.
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.
Despite those points, 2025 still ended up as the third-hottest year in over 175 years of record-keeping and likely one of the warmest in at least several thousand years. It was nearly as warm as 2023, at 2.6 degrees Fahrenheit (1.47 Celsius) above the 1850-1900 average, according to the European Union’s Copernicus Climate Change Service. It also had the second-highest average land temperature recorded, up 3.6 F (2 C) compared to preindustrial years, with more than 10% of the land experiencing record-high temperatures.
Factors that made 2025 warmer than expected
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.
Rising energy demand drove an increase in fossil fuel use. About 80% of the increasing electric power demand came from emerging economies, largely for rising air conditioning demands as the world gets hotter. In the U.S., the rapid growth of data centers for AI and cryptocurrency mining helped boost U.S. carbon dioxide emissions by 2.4%.
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.
https://datawrapper.dwcdn.net/t0SSd/1
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%.
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.
Solar output will continue to decrease slowly in 2026. However, the International Monetary Fund projects strong global economic growth at about 3.3%, suggesting electricity demand will also continue to grow. The International Energy Agency expects global electricity demand to increase by 3.6% per year through at least 2030.
Even though global renewable energy use is growing quickly, it isn’t growing fast enough to meet rising demand, meaning more fossil fuel use in the coming years. More fossil fuels burned means more emissions and more warming, while the ability of the ocean and land to absorb carbon dioxide continues to decrease. As a result, the atmosphere and oceans heat up, increasing the risks of passing tipping points – glaciers disappear, Atlantic Ocean circulation shuts down, permafrost thaws, coral reefs die.
If greenhouse gas emissions continue at a high rate, humanity may look back at 2025 as one the coolest years globally in the rest of our lives.
Michael Wysession, Professor of Earth, Environmental, and Planetary Sciences, Washington University in St. Louis
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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Last Updated on March 8, 2026 by Daily News Staff
How the polar vortex and warm ocean intensified a major US winter storm
Mathew Barlow, UMass Lowell and Judah Cohen, Massachusetts Institute of Technology (MIT)
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.
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.
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.
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.
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.
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.
The biggest swings in the jet stream are associated with the most energy. Under the right conditions, that energy can bounce off the polar vortex back down into the troposphere, exaggerating the north-south swings of the jet stream across North America and making severe winter weather more likely.
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.
Some research suggests that even in a warming environment, cold events, while occurring less frequently, may still remain relatively severe in some locations.
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.
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.
The opposing effects make it complicated to assess the potential change to average storm strength. However, intense events do not necessarily change in the same way as average events. On balance, it appears that the most intense winter storms may be becoming more intense.
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.
This article, originally published Jan. 24, 2026, has been updated with details from the weekend storm.
Mathew Barlow, Professor of Climate Science, UMass Lowell and Judah Cohen, Climate scientist, Massachusetts Institute of Technology (MIT)
This article is republished from The Conversation under a Creative Commons license. Read the original article.
The science section of our news blog STM Daily News provides readers with captivating and up-to-date information on the latest scientific discoveries, breakthroughs, and innovations across various fields. We offer engaging and accessible content, ensuring that readers with different levels of scientific knowledge can stay informed. Whether it’s exploring advancements in medicine, astronomy, technology, or environmental sciences, our science section strives to shed light on the intriguing world of scientific exploration and its profound impact on our daily lives. From thought-provoking articles to informative interviews with experts in the field, STM Daily News Science offers a harmonious blend of factual reporting, analysis, and exploration, making it a go-to source for science enthusiasts and curious minds alike. https://stmdailynews.com/category/science/
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What Is a Gustnado?
A gustnado may look like a tornado, but it’s a different weather phenomenon. Learn what a gustnado is, how it forms, and why it’s usually weaker.
Last Updated on December 18, 2025 by Daily News Staff
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.
Learn the differences between tornadoes, dust devils, and other rotating weather phenomena in our STM Daily News Knowledge Series.
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