On an iconic Colorado 14er, climate change is shifting the timing between flowers and pollinators

University of Colorado at Boulder

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Pseudomasaris vespoides, a pollen wasp is showing up much earlier than it used to in the historical study. 

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Credit: Julian Resasco/CU Boulder

Warming temperatures and earlier snowmelt are disrupting the long-running relationship between wildflowers and their pollinators on Colorado’s Pikes Peak.

In a new study published September 25 in the American Naturalist, researcherss at the University of Colorado Boulder found many of the region’s plants and pollinators are now emerging earlier in the spring than they did a century ago. But some species are falling out of sync, potentially adding challenges for pollinators already under threat.   

“Pollinators are so important to our ecosystem, supporting everything from wildflowers to the food we eat,” said Julian Resasco, the paper’s senior author and associate professor in the Department of Ecology and Evolutionary Biology. “Having data from 100 years ago gave us a unique opportunity to take a glimpse of these long-term trends under a changing climate.”

Starting in 1910, ecologist Frederic Clements and his student Frances Long began documenting the interactions between local plants and their pollinators at the now-closed Carnegie Institution’s Alpine Laboratory on the slope of the 14,115-foot Pikes Peak near Colorado Springs. 

Over the past century, Colorado has warmed by an average of 2.9°F, with the average winter temperature rising even faster, by 3.3°F. Climate change has also decreased the amount of snow accumulating on top of the mountains, or snowpack, in the western United States, reducing the amount of water available for mountain species in spring and summer.

Warming temperature and snowmelt are vital environmental cues for plants and insects to emerge from their winter inactive state. 

As the climate warms and snow melts earlier, plants may begin flowering sooner and pollinators may start flying earlier. But not all species respond to it in the same way or at the same pace, said Leana Zoller, the paper’s first author and a former postdoctoral associate at CU Boulder. 

Resasco, Zoller and their team returned to Clements and Long’s study area to see if the interactions between plants and pollinators have shifted over the past century. Because Pikes Peak is a protected wilderness area, its environment has remained largely undisturbed. This allowed the team to study the impact of climate change without other influences such as land use change.

Between 2019 and 2022, the research team analyzed 25 wild pollinator species, including bumblebees, wasps and flies, as well as 11 flowering plants the insects interact with, forming 149 pairs of interactions. 

Of the species that could be compared between the historical and contemporary datasets, they found that wildflowers were blooming about 17 days sooner than a century ago, and pollinators started to fly 11 days earlier.  

Out of the 149 pairs of plant-pollinator comparable interactions, nearly 80% have more overlap in their active periods than before. While this trend appears beneficial for pollinators now, the advantage may be short-lived. 

Historically, pollinators were active earlier than plants started flowering. “In our study system plants have advanced more rapidly than pollinators. If the trends continue, we may see plants flower before pollinators become active in the future,” said Zoller, who is currently a postdoctoral associate at Cornell University in Ithaca, New York. 

“Mismatches may occur among these currently overlapping pairs as plants and pollinators continue to respond differently to changing conditions,” she added.

Some species are already slipping out of sync. 

The western bumblebee, for example, is emerging 12 days later than a century ago, which could leave it struggling to find enough food. Once common and widespread in the western United States and Canada, this species has sharply declined by at least 57% since 1998 due to a mix of disease, habitat loss and pesticides.

“This mismatch in the schedules of western bumblebees and the plants they historically fed on could add another stressor on top of everything else this species is facing,” Resasco said. 

Pollinators, including domestic honeybees and wild species, contribute to the reproduction of 75% of the world’s flowering plants and about 35% of the world’s food crops. Their decline could have far-reaching effects on both natural landscapes and agriculture.

“Wild pollinators help maintain the biodiversity of plants in our ecosystems. We have a responsibility to make sure they don’t disappear,” Resasco said. 

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Journal

The American Naturalist

DOI

10.1086/738351 

 

Fire in the sky: Strong summer storms in the Midwest send wildfire smoke into the previously pristine stratosphere

Aerosols and burning biomass may affect heating and energy absorption in the ozone, leading to faster warming and unexpected climate effects

Purdue University

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Dan Cziczo, a storm expert at Purdue University, found that strong summer storms in the Midwest are punching wildfire smoke up into the stratosphere — a previously pristine part of the atmosphere. (Purdue University photo/John Underwood)

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Credit: (Purdue University photo/John Underwood)

WEST LAFAYETTE, Ind. — Gully warsher. Duck drownder. Toad strangler. Cob floater. Sod soaker.

Whatever their names, summer in the Midwest isn’t summer without strong, sudden storms with towering clouds. While the Indian subcontinent is famous for its monsoon season, what many people don’t know is that the midwestern United States has its own monsoon season, very nearly as strong.

And those Midwest monsoons, increasingly, are breaking through the ceiling of the sky and into the stratosphere, a typically undisturbed layer of the atmosphere, introducing burning biomass and aerosols from western wildfires with potentially concerning consequences for the ozone layer and the climate.

Like a hole in the hull of a boat leaking in dirty seawater, these storms allow aerosols and particles in from the lower atmosphere, new research shows.

The research was conducted in partnership with NASA using a high-altitude research aircraft taking measurements in the remote reaches of the stratosphere. Dan Cziczo, a professor in the Department of Earth, Atmospheric, and Planetary Sciences in Purdue’s College of Science, led the team in conjunction with research scientist Xiaoli Shen. The paper published in Nature Geoscience.

“In the summer, here in the Midwest particularly, we get all these air quality warnings from wildfires because the climate is getting warmer and the land is getting drier,” Cziczo said. “That’s becoming more common, but that’s all close to the planet’s surface, where we thought it was staying. We flew this research aircraft up into the stratosphere, the next layer up of the atmosphere, which should be separate. Stratosphere means stratified; it should be separate. But what we found is that during these big wildfire seasons, the lower part of the stratosphere is just littered with these biomass particles.”

A rent in the vault of heaven

Cziczo and his team study the mechanics of the atmosphere, especially how, why, when and where clouds and storms form. They are especially interested in the way that warm, wet air moves up from the Gulf of Mexico, crashes against the Rocky Mountains and forms severe summer storms and rain, much like summer monsoon in India forms when warm, wet winds collide with the Himalayas.

Big storms and clouds typically can’t expand beyond the layer of pressure and wind that marks the change between the troposphere, the layer of the atmosphere closest to the ground, and the stratosphere — it’s why so many clouds look like buttes or mesas with flat tops.

But that’s not always true. Like a titan punching up through the cloud layer, the top of the storm can become too powerful to be contained and erupt into the stratosphere itself in a formation called an overshooting top. It is a fountain of cloud, a geyser of storm that erupts into the peaceful protective layer of the stratosphere. As it gushes up, it brings with it a burst of air, along with currents of aerosol, and anything in the air below it — including pollutants, aerosols and burning biomass.

Earth’s atmosphere is the sheer bubble that protects of our planet like a snow globe. The stratosphere is the realm of the ozone layer, the buffer that absorbs so much of the sun’s radiation and helps keep Earth from turning into a Venusian hothouse.

Typically, the only particles that make it up into the stratosphere come from rare, globally notable and dramatic events — violent volcanoes and massive meteors. The incursions scientists found in this study aren’t necessarily chinks in the planet’s armor — yet. But they might be microfractures. And scientists aren’t sure yet what kind of effects these alterations might have.  

“This could be a really big deal for a number of reasons,” Cziczo said. “For one thing, for so long, we’ve assumed the stratosphere is a pristine area. But what this shows is that human impacts through a changing climate can affect the chemistry and the radiative ability of the stratosphere.

These particles can interact with sunlight and heat up, warm the stratosphere. It could affect its stability — which is vital to the planet.”

It’s not just the summer storms, either. Sometimes the wildfires themselves get so large that they create their own weather — directly generating their own storm clouds, called pyrocumulus, so strong that they catapult their own burning ash and biomass directly into the stratosphere above the fire. Cziczo notes that they observed this in the fires over Australia in the 2019 bush fire season, but that, as storm season warms, dries and increases in severity, this effect is becoming more frequent.

“There are actually two ways for this stratosphere puncture to happen,” Cziczo said. “It can be the one severe fire, but it can also be a bunch of little fires that are just constantly perturbing the stratosphere in a way that we didn’t recognize before.”

Up and away into the wild blue yonder

The stratosphere is a high and lonely place — usually the domain only of military aircraft, weather and research balloons, the grounded Concorde, and spacecraft passing through on their way up or down, as well as a few remarkable weather phenomena including red sprites and blue jet lightning.

To study it, NASA built a variant of the Lockheed Martin U-2 aircraft — dubbed ER-2 for Earth Resources 2. Equipped to sniff out aerosols, particles, and shifts in pressure, temperature, humidity and wind rather than adversarial forces and resources, the plane can reach altitudes of 70,000 feet — higher than 95% of the Earth’s atmosphere with an effective horizon of 300 miles. (In comparison, the reduced gravity aircraft — also called “vomit comets” — which frequently help train astronauts and conduct low-gravity science experiments, only reach altitudes of about 35,000 feet.)

Those two planes are based in California at the NASA Armstrong Flight Research Center, and the storms were happening in the Midwest, prompting one to temporarily transfer to Kansas.

“What’s kind of interesting about this, and this is one of these things that I’m not sure that everybody knows about, is that North America has a monsoon,” Cziczo said. “Most of us have heard about the Asian monsoon over the Indian subcontinent; these powerful storms that crash up against the Himalayas and drop all this rain. The Midwest has something analogous to that, and it is called the North American monsoon. Warm, wet air from the Gulf of Mexico comes up and gets hung up on the Rockies. That’s what creates a lot of those powerful thunderstorms over the Midwest and through the Great Plains area. That’s why we wanted to be in Kansas during the summertime; you can reach all these different systems from there. We flew up into Wisconsin, Illinois, Indiana, Upper Midwest, Great Plains and all over. I think we even got as far as Texas.”

The ER-2, which has been active since the 1980s, is equipped to measure minute changes in air quality and chemistry, allowing Cziczo and his team to track the footprints of the summer storms and fires through the stratosphere.

“Using these very sophisticated tools, we were able to tell that it’s not that we’re just throwing a bunch of tropospheric air and putting it in the stratosphere,” Cziczo said. “Putting this particulate matter in the stratosphere changes the dynamics; it changes the chemistry, and it changes the way that part of the atmosphere works. It changes the way it handles heat — it heats it up faster. And that’s what we’re worried about. That’s what we really need to investigate, to understand. We went to all this trouble to save the ozone layer.”

This research was funded by NASA’s Earth Science Project Office.

About Purdue University

Purdue University is a public research university leading with excellence at scale. Ranked among top 10 public universities in the United States, Purdue discovers, disseminates and deploys knowledge with a quality and at a scale second to none. More than 106,000 students study at Purdue across multiple campuses, locations and modalities, including more than 57,000 at our main campus locations in West Lafayette and Indianapolis. Committed to affordability and accessibility, Purdue’s main campus has frozen tuition 14 years in a row. See how Purdue never stops in the persistent pursuit of the next giant leap — including its integrated, comprehensive Indianapolis urban expansion; the Mitch Daniels School of Business; Purdue Computes; and the One Health initiative — at https://www.purdue.edu/president/strategic-initiatives.

Note to journalists:

Photos of Dan Cziczo and the ER-2, as well as a photo of an overshooting top are available on Google Drive. 

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Journal

Nature Geoscience

DOI

10.1038/s41561-025-01821-1 

Article Title

Stratospheric aerosol perturbation by tropospheric biomass burning and deep convection

Article Publication Date

13-Oct-2025

 

Most of California Wine Country’s agricultural workers have been exposed to wildfires, new survey finds

By partnering with the community, UC Berkeley researchers conducted a sweeping survey of California farmworkers on their experience working during wildfires.

University of California - Berkeley

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Sonoma County is known for its rolling fields and famed vineyards, making the region a pillar in California’s wine industry. But a sweeping new survey from UC Berkeley has found that approximately 75% of agricultural workers there have worked during wildfires since 2017, raising questions about worker safety and a program that could further expose workers during wildfire evacuations. 

About half of the 1,000-plus farmworkers who participated in the study reported having ailments like headaches or sore throats after working during a wildfire. Half reported a lack of health insurance, and many worked while feeling ill due to a fear of losing their jobs or not being able to afford basic needs due to lost wages. 

What’s more, a new program meant to ensure that the people who harvest grapes, tend livestock and irrigate fields can continue to work during wildfire evacuations may force workers to choose between their health or paying their bills, according to a policy-focused white paper accompanying the survey findings. 

Led by scholars from the School of Public Health and the Human Rights Center, the research was published today (Oct. 20) in the Journal of Agromedicine. The coinciding white paper calls attention to potential improvements to what’s called the Agricultural Access Verification Card Program — “Ag Pass” for short. 

“The most consistent theme throughout the surveys and interviews was that farmworkers felt it necessary to work in hazardous conditions … to be able to pay for basic needs such as housing and groceries,” the study says. 

The findings for both reports stem from a multiyear community-engaged research project and add critical understandings of the conditions and challenges facing agriculture workers in Wine Country and across California. 

At a time when health care and housing costs are already high, and fires present recurring challenges for communities across the state, the researchers hope the work can inform policy around agricultural workers and improve efforts to keep them safe during disasters. 

“We know farmworkers are going to continue to work in really dangerous conditions,” said Carly Hyland, an assistant professor in the School of Public Health and lead author of the study. “And so I think we’re continuing to strategize about how we can make that as safe as possible for workers.”

Project beginnings

In 2020, approximately one-quarter of wine grapes were believed to have gone unpicked due to lightning-sparked wildfires and effects from the COVID-19 pandemic. It was a major hit to an industry whose future is already uncertain due to changing habits around alcohol consumption, inconsistent weather due to climate change and intermittent wildfires that can bring operations to a standstill. 

The issue hasn’t been limited to vineyards. Elsewhere in California, wildfires have forced evacuations of cattle ranches and other agricultural operations, leaving animals and crops vulnerable and unattended to. Even if it was safe enough for someone to access a livestock operation during a wildfire, the policies surrounding who and how were uneven and unclear.

“Under the evacuation laws at that time, there was no clear way to do that,” said Linda Gordon, a climate researcher at Berkeley’s Human Rights Center and co-author of the new research. “Each county was designing their own programs, if any. There was very little oversight.” 

To clarify things, California lawmakers in 2021 passed legislation authorizing counties to develop a program for approved livestock producers or managers to access properties during disasters. The Sonoma County Board of Supervisors expanded the program to include commercial agricultural operations and all full-time employees, meaning people who tend crops could bypass closures and access vineyards.

While the county’s agricultural office collects basic details about workers and administers the Agricultural Access program, the sheriff’s office distributes passes and decides when and how to activate it. 

Gordon began studying Ag Pass as a law student two years ago. She was concerned it lacked clear input from public health officials and might put those who were expected to work behind evacuation lines at risk. She connected with Hyland, who — with the help of community partners — was already studying the effects of extreme heat, pesticide exposure and wildfire smoke on California farmworkers. 

“This Ag Pass program is really specifically focused on reentering an evacuation zone and does not take into consideration potential health or safety impacts on farmworkers,” Hyland said. “Totally separate from that is, even if an area isn’t evacuated, we know that it can still be really dangerous for farmworkers to be working in.”

‘Like an angel fell from the sky’

Gordon and Hyland knew that if they wanted to accurately document the experiences of agricultural workers, they’d need the help of someone with deep community connections. So they turned to Zeke Guzman.

Guzman is president of the farmworker advocacy group Latinos Unidos del Condado de Sonoma. When he talks about his interest in farmworker safety during fires, he describes his experience during the 2019 Kincaid Fire, when he helped arrange the delivery of more than 600 homemade burritos to a makeshift evacuation site. 

It was the start of his work during wildfires, but it wouldn’t be the end. 

As fires continually flared in subsequent years, Guzman became increasingly concerned about the health effects the smoke was having on those harvesting grapes.

As much as he tried to bring greater attention to the issue, he felt like he was hitting resistance. Then one day in 2022, he received a call from Hyland. 

“It was like an angel fell from the sky,” he said.

Farmworkers can be a hard-to-reach group who may be hesitant to speak with university researchers. After some discussions about the goals of the Berkeley project, Hyland asked if Guzman might be able to help them survey 200 workers. 

He paused. 

“No, probably not,” Guzman said. “But I can get 1,000.”

Community research underway

Guzman and the Berkeley researchers established a six-person community-engagement team from trusted nonprofits and health centers. Together, they developed and refined survey questions and a plan to get it in the hands of as many people as possible — a core tenet of community-engaged research.

Guzman said the process made the community “feel like their voice was important.”

It also led to compelling results. 

With the help of a team of Berkeley undergraduate students and the community partners, the research assistants fanned out in the community, from churches and health clinics to individuals’ homes known to be community hubs. Smaller group settings and recruiting through different messaging apps helped expand the sample size and led to more honest results, the team said.

In spring 2024, they collected 1,011 surveys. It was among the largest recent farmworker surveys in the region — and it surpassed what Hyland and Gordon imagined possible.

“The community engagement team was what made it possible for us to recruit that many participants,” Hyland said. “It again underscores the importance of working with trusted community partners and really listening to them and having them advise us on how to go about doing this work.”

“I really firmly believe not just that it can’t, but that this work shouldn’t be done without local partners,” Hyland added.

The results revealed in new depth the concerns workers had about working in fire zones, the skepticism they held toward the law enforcement agency that administers the program and the barriers to health care tools before they’re exposed to smoke and after they develop symptoms of illness or longer-term disease. 

At the time of the survey, the Ag Pass program had not yet been activated, so the research focused more broadly on previous experiences and sought to understand how the program was understood within the community. 

The vast majority of participants had not even heard of it, and roughly half said information about the program was inaccessible or were hesitant to have their picture taken by the sheriff’s office. They also showed a preference for interacting with community organizations and local health clinics, rather than county government entities.

Pamphlets alone were ineffective. Videos or input from knowledge experts — like in community clinics — would be a more effective way to learn about safety steps during fires, respondents said. 

Ultimately, there’s a bigger economic challenge to overcome, the study found.

“To be honest, it is very hard to stop work, and even if we were in danger because of the wildfires or the smoke or bad quality of air, we still have to work,” one participant said. “We do not have any other form of income.”

Besides pointing to what Hyland said was a “clear tension between health and economic security,” the research team says there are specific steps that can be taken to improve the program. 

At the county level, public health input should become part of the consideration on when to activate it, instead of relying exclusively on the sheriff’s office. The county should also create a data privacy policy that clarifies for the public how personal information collected for the application is stored, shared and protected. Increased outreach in Spanish and Indigenous languages, and collaboration with community groups could help increase trust and engagement with farmworkers, the team said. 

At the state level, the research team said there needs to be an economic safety net for farmworkers who currently cannot pay their bills without working in dangerous conditions. State health agencies should also enforce health and safety laws during wildfires and inside evacuation zones. 

“We can’t design California’s resilient climate policies without thinking about the people who will be most vulnerable and impacted by them when a wildfire hits,” Gordon said.

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Method of Research

Survey

Subject of Research

People

Article Title

Evaluation of “Agricultural Pass” Program and Farmworkers’ Experiences Working During Wildfires in Sonoma County, California

Article Publication Date

20-Oct-2025