Climate & Environment

Researchers wake up microbes trapped in permafrost for thousands of years

Daniel William Strain — Thu, 02 Oct 2025 17:41:38 +0000

Researchers wake up microbes trapped in permafrost for thousands of years Daniel William… Thu, 10/02/2025 - 11:41

Daniel Strain

Thawing permafrost in Alaska. (Credit: Brandt Meixell/USGS)

In a new study, a team of geologists and biologists led by CU Boulder resurrected ancient microbes that had been trapped in ice—in some cases for around 40,000 years.

The study is a showcase for the planet’s permafrost. That’s the name for a frozen mix of soil, ice and rocks that underlies nearly a quarter of the land in the northern hemisphere. It’s an icy graveyard where animal and plant remains, alongside plentiful bacteria and other microorganisms, have become stuck in time.

That is, until curious scientists try to wake them up.

The group discovered that if you thaw out permafrost, the microbes within will take a while to become active. But after a few months, like waking up after a long nap, they begin to form flourishing colonies.

“These are not dead samples by any means,” said Tristan Caro, lead author of the study and a former graduate student in geological sciences at CU Boulder. “They’re still very much capable of hosting robust life that can break down organic matter and release it as carbon dioxide.”

The U.S. Army Corps of Engineers’ Permafrost Tunnel near Fairbanks, Alaska. (Credit: Tristan Caro)

Robyn Barbato of the Cold Regions Research and Engineering Laboratory drills a sample from the walls of the Permafrost Tunnel. (Credit: Tristan Caro)

Caro and his colleagues published their findings in September in the journal JGR Biogeosciences.

The research has wide implications for the health of the Arctic, and the entire planet, added study co-author Sebastian Kopf.

Today, the world’s permafrost is thawing at an alarming rate because of human-caused climate change. Scientists worry this trend could kick off a vicious cycle. As permafrost thaws, microbes living in the soil will begin to break down organic matter, spewing it into the air as carbon dioxide and methane—both potent greenhouse gases.

“It’s one of the biggest unknowns in climate responses,” said Kopf, professor of geological sciences at CU Boulder. “How will the thawing of all this frozen ground, where we know there’s tons of carbon stored, affect the ecology of these regions and the rate of climate change?”

Long slumber

To explore those unknowns, the researchers traveled to a one-of-a-kind location, the U.S. Army Corps of Engineers’ Permafrost Tunnel. This unusual research facility extends more than 350 feet into the frozen ground beneath central Alaska.

When Caro entered the tunnel, which is about as wide as a mine shaft, he could see the bones of ancient bison and mammoth sticking out from the walls.

“The first thing you notice when you walk in there is that it smells really bad. It smells like a musty basement that’s been left to sit for way too long,” said Caro, now a postdoctoral researcher at the California Institute of Technology. “To a microbiologist, that’s very exciting because interesting smells are often microbial.”

In the current study, the researchers collected samples of permafrost that was a few thousand to tens of thousands of years old from the walls of the tunnel. They then added water to the samples and incubated them at temperatures of 39 and 54 degrees Fahrenheit—chilly for humans, but downright boiling for the Arctic.

“We wanted to simulate what happens in an Alaskan summer, under future climate conditions where these temperatures reach deeper areas of the permafrost.” Caro said.

With a twist: The researchers relied on water made up of unusually heavy hydrogen atoms, also known as deuterium. That allowed them to track how their microbes drank up the water, then used the hydrogen to build the membranes made of fatty material that surround all living cells.

Arctic summers

What they saw was surprising.

In the first few months, these colonies grew at a creep, in some cases replacing only about one in every 100,000 cells per day. Under lab conditions, most bacterial colonies completely turn over in the span of a few hours.

But by the six-month mark, that all changed. Some bacterial colonies even produced gooey structures called “biofilms” that you can see with the naked eye.

Caro said these microbes likely couldn’t infect people, but the team kept them in sealed chambers regardless.

He added that the colonies didn’t seem to wake up that much faster at hotter temperatures. The results could hold lessons for thawing permafrost in the real world: After a hot spell, it may take several months for microbes to become active enough that they begin to emit greenhouse gases into the air in large volumes.

In other words, the longer Arctic summers grow, the greater the risks for the planet.

“You might have a single hot day in the Alaskan summer, but what matters much more is the lengthening of the summer season to where these warm temperatures extend into the autumn and spring,” Caro said.

He added there are still a lot of open questions about these microbes, such as whether ancient organisms behave the same at sites around the world.

“There’s so much permafrost in the world—in Alaska, Siberia and in other northern cold regions,” Caro said. “We’ve only sampled one tiny slice of that.”

Across the Arctic, bacteria and other microorganisms have become trapped underground in frozen soil and ice. A new study finds that these ancient microbes may still be capable of forming thriving colonies.

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Corals might be adapting to climate change

Yvaine Ye — Wed, 01 Oct 2025 03:09:31 +0000

Corals might be adapting to climate change Yvaine Ye Tue, 09/30/2025 - 21:09

Yvaine Ye

Corals, the foundation of ocean biodiversity, are threatened by climate change. But new research suggests that these organisms might be more resilient than previously thought.

In a study published August 27 in Science Advances, a CU Boulder researcher showed that despite a gradual increase in ocean acidity levels over the past 200 years, some corals seem to be able to adjust and continue to generate their hard, stony skeleton structures.

Jessica Hankins taking a coral sample. (Courtesy of Jessica Hankins)

“We found that corals were able to regulate the mechanism they use to build and maintain their skeletons despite the ocean becoming more acidic,” said Jessica Hankins, the paper’s first author and a PhD student in the Department of Geological Sciences. “It’s an unexpected and hopeful signal; however, we need more long-term data to know what it really means.”

As corals grow, they form their skeletons by absorbing ions from seawater into a space between the existing skeleton and the soft tissue above called the coral calcifying fluid. The coral has ways to regulate the chemistry of this fluid to make conditions ideal so that calcium and carbonate ions can combine to form calcium carbonate, the material coral skeletons consist of.

The ocean absorbs about 30% of carbon dioxide emissions from human activities. As more CO₂dissolves in the ocean, the seawater undergoes a chemical reaction that makes the ocean surface more acidic. Previous studies suggest that ocean acidity has increased by 40% since the Industrial Revolution and is likely to rise further.

This shifts the balance of carbon species in seawater, resulting in fewer carbonate ions available in seawater, something that corals need to build their skeleton.

Scientists have predicted that ocean acidification would make it harder for corals to grow and maintain their skeletons, leading to less dense structures that are more prone to breakage. But prior experiments in the laboratory and in the wild have yielded unclear results.

Hankins set off to study long-lived coral skeletons using an advanced imaging technology called Raman spectroscopy.

Raman spectroscopy uses lasers to reveal uses lasers to reveal the chemical makeup and molecule arrangement in objects like rocks, paintings and proteins. This method could show detailed information about coral skeleton chemistry, said Hankins, who is also the manager of CU Boulder’s Raman Microspectroscopy lab.

Corals in the Great Barrier Reef off the coast of Australia. (Courtesy of Jessica Hankins)

When corals rapidly form the calcium carbonate mineral that composes their skeletons, which typically occurs when more carbonate ions are available, the resulting structures tend to contain other minerals extracted from seawater. These “impurities” affect the molecular arrangement and structure of calcium carbonate, showing an increase in the chaos of the coral skeleton under Raman spectroscopy.

“When conditions are favorable, corals seem to prioritize growth, even if that means producing skeletons that are a bit more disordered at the molecular level,” Hankins said.

Hankins studied two pieces of coral skeleton, one nearly 200 years old and one 115 years old, from the Great Barrier Reef and the Coral Sea located off the northeastern coast of Australia. Using Raman spectroscopy, she found that both corals were able to regulate their internal fluid chemistry to maintain growth of their skeleton, despite an ongoing increase in ocean acidity due to ocean acidification. The corals appeared to be able to sustain the production of calcium carbonate even as the chemistry of the surrounding seawater grew less hospitable.

While it remains unclear how the corals adapted to the changing environment, Hankins said the secret might lie in their calcifying fluid.

“It could be that the processes corals use to modify and regulate their calcifying fluid are more complex than we’ve been able to constrain previously,” said Hankins. “More studies are needed to determine if different species, or if the same species in a different location, have similar responses,” she said.

In addition to ocean acidification, corals still face increasing stress from warming sea surface temperatures, human-induced pollution, and unsustainable fishing practices, Hankins said. Between 2023 and mid-May 2024, scientists have confirmed mass coral bleaching in at least 62 countries and territories worldwide. Coral bleaching occurs when corals expel the algae living in their tissues under stressful conditions, such as high ocean temperatures, causing them to turn completely white.

Coral reefs are the backbone of one of the largest ecosystems in the world. They protect shorelines threatened by erosion and storm damage, while providing marine organisms with a habitat, nursery, and spawning grounds.

“Corals provide the physical framework that reef ecosystems depend on. If they consistently grow weaker, less dense skeletons, it could trigger a domino effect that leads to a broader ecological collapse,” Hankins said. “The ocean may feel distant from Colorado, but it’s not separate. Every system on earth is connected. What happens to coral reefs reverberates far beyond the shore.”

A new study of corals up to 200 years old suggests that the organisms are showing signs of resilience to the impacts of an increasingly acidic ocean.

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Corals in the Great Barrier Reef off the coast of Australia. (Courtesy of Jessica Hankins)

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Corals in the Great Barrier Reef off the coast of Australia. (Courtesy of Jessica Hankins)

Fixing solar's weak spot: Why a tiny defect could be a big problem for perovskite cells

Megan Maneval — Wed, 24 Sep 2025 12:47:53 +0000

Fixing solar's weak spot: Why a tiny defect could be a big problem for perovskite cells Megan Maneval Wed, 09/24/2025 - 06:47

Solar energy is a crucial part of our clean energy future, but a new highly efficient solar material has a hurdle that needs to be addressed. A recent study reveals how a microscopic weak spot can lead to total device failure and what to do about it.

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Students study metal contamination in Colorado waterways

Megan Maneval — Thu, 18 Sep 2025 20:45:05 +0000

Students study metal contamination in Colorado waterways Megan Maneval Thu, 09/18/2025 - 14:45

A team at CU Boulder is studying heavy metal pollution in a watershed near Aspen. Their efforts have a dual goal: contributing to clean-up efforts and studying the potential of recovering some of the metals.

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CUriosity: The aspens are changing color in Colorado. Why do they do it?

Yvaine Ye — Wed, 17 Sep 2025 21:06:20 +0000

CUriosity: The aspens are changing color in Colorado. Why do they do it? Yvaine Ye Wed, 09/17/2025 - 15:06

Yvaine Ye

In CUriosity, experts across the CU Boulder campus answer pressing questions about humans, our planet and the universe beyond.

This week, plant biologist Barbara Demmig-Adams answers: “Why do leaves change color in the fall?”

Varsity Lake was awash in Fall colors during the 2024 Family weekend on the CU Boulder campus. (Credit: Glenn J. Asakawa/CU Boulder)

Autumn paints Colorado’s mountains in light and color.

Barbara Demoing-Adams

Bands of yellow and orange aspen trees ripple across the slopes, flickering against the dark green of conifer forests. The display is dazzling, but leaves don’t change color just for decoration. The transformation is the result of a chemical process inside each leaf that helps trees prepare for the coming winter, says plant biologist Barbara Demmig-Adams.

“Trees have developed different strategies so they can survive with limited resources and avoid competing with each other,” says Demmig-Adams, professor of distinction in the Department of Ecology and Evolutionary Biology. “That’s why we see some leaves turn yellow, some turn red and some stay green.”

Changing leaf color is a unique trait of deciduous trees, a group that includes aspens, maples and oaks. These species have broad leaves that they shed in the fall. Evergreen trees, like pines and firs, stay green through the seasons.

Previously in CUriosity

How do emergency alerts work, and where do they fall short?

Or read more CUriosity stories here

During spring and summer, when sunlight is abundant, deciduous trees produce chlorophyll, a green pigment that captures light and turns it into food through photosynthesis.

As temperatures drop and days shorten in the fall, deciduous trees stop producing chlorophyll and begin pulling nutrients, especially nitrogen, back into their trunks and roots before shedding the leaves.

Without chlorophyll, the yellow and orange pigments that have been present in the leaves all along shine through.

“The yellow pigment is mainly composed of carbon, which is abundant in the environment and in the plants, so trees are fine with letting it fall away,” Demmig-Adams says.

Red leaves tell a different story. Unlike the yellow pigment, trees make the red pigments, called anthocyanins, freshly in the fall.

When trees experience a succession of warm, sunny Autumn days, their leaves produce lots of sugar. If the nights become significantly cooler, the veins that carry fluids into and out of the leaves close off, trapping sugar inside. That sugar then binds with other chemical molecules to form anthocyanins.

This year, fall foliage started to emerge in the Front Range in late August, weeks earlier than the typical mid-September timing. This is mainly because of the drought conditions Colorado is experiencing, which triggered the color-changing process early as trees try to conserve nutrients.

“Trees are very smart. They’re always keeping track of all of the changes in the environment and respond promptly,” Demmig-Adams says.

Colorado's golden autumn colors are emerging as trees prepare for winter. This process is driven by quiet chemical changes inside each leaf.

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US to retire its only icebreaker, stranding polar research

Yvaine Ye — Tue, 16 Sep 2025 15:17:14 +0000

US to retire its only icebreaker, stranding polar research Yvaine Ye Tue, 09/16/2025 - 09:17

Stephanie Maltarich

On Sept. 10, the U.S. National Science Foundation announced that the agency is terminating the lease for Nathaniel B. Palmer Icebreaker, the sole U.S. icebreaker dedicated to Antarctic research.

This move, which came as a result of budget cuts under the current administration, worries polar researchers, including Naomi Ochwat, a postdoctoral researcher in CIRES’ Earth Science and Observation Center.

Ochwat is a glaciologist who studies the changes on the edges of Antarctic glaciers and how they relate to climate change. Decades of data collection conducted from the decks of the Palmer has been integral to her work.

“There was a cruise back in 2006, where the Palmer went to an area that I study on the Antarctic Peninsula,” Ochwat said. “It was one of the few times the sea ice was actually low enough that they could reach the front of the glaciers that I study. Now 17 years later, I've used that data, and it's been very important for the research I've done.”

As the National Science Foundation plans to decommission the Palmer after it returns from its last expedition this October, Ochwat shares her take on what’s at stake.

Why is the Palmer icebreaker important for United States’ Antarctica research?

We are currently a global leader in Antarctic research and Antarctic exploration, where the Palmer is an integral aspect of the U.S. Antarctic Program.

Earth’s climate is rapidly changing, and in order to understand the extent of those changes, we need to know what's happening in Antarctica, especially along the glacier edges, where we have a lot of drastic changes happening right now. Antarctica is really far away, and we rely heavily on research vessels to get there.

The Ross Ice Shelf at the Bay of Whales, Antarctica, and the Palmer in the background. (Credit: Michael Van Woert/ NOAA)

Are there other reasons beyond research?

Antarctica is a very special place because nobody owns the continent, and so you don't have any official territories or any kind of land ownership. As long as you are on the Antarctic Treaty, you can go to Antarctica to study it, following the treaty rules. So it’s important to be able to say we have a presence in Antarctica.

Having research stations and these research vessels puts us at the forefront of science and the forefront of Antarctic science and exploration on a global scale.

Why do polar researchers need a designated ice-breaking vessel?

Parts of Antarctica have persistent sea ice year round that can restrict access to areas along the coast. The sea ice can be several meters thick in some places, and you don't have the ability to wait for it to melt out, so you absolutely need an ice breaker in order to go through the sea ice. You have a very short period of time in which you can go to Antarctica—the sea ice has its own schedule.

What does it look like to conduct research on the Palmer?

You’re usually at sea for at least a month, and you're doing research that entire time, except when you're crossing the Drake Passage (between the tip of South America and the Antarctic Peninsula) which is known to be very rough seas. It’s equipped with enough supplies so scientists can spend large amounts of time doing research without having to return to port. I’ve never been on the ship, but the data it collected has been vital to my research.

In 2006, the ship went to the eastern side of the Antarctic Peninsula to the Larsen B Embayment, and it collected multi-beam bathymetry data, meaning it mapped the topography of the sea floor. This dataset has allowed me to investigate the role of the bed topography on the 2022–24 glacier retreats in this area.

How does Antarctic research impact everyday Americans?

If we’re talking about sea level rise, we've already seen the kind of flooding that can happen with storm surges, which have been exacerbated by sea level rise. So, you're not going to be able to live on the coast because your house insurance is going to be skyrocketing, or your job in your warehouse that was right on the coast is going to be flooded, and now you can't work there.

People are going to move, and I think that's one of the biggest things with climate change and sea level rise. It is not so much that the sea is rising, but more that people are going to have to relocate because of it.

CU Boulder Today regularly publishes Q&As with our faculty members weighing in on news topics through the lens of their scholarly expertise and research/creative work. The responses here reflect the knowledge and interpretations of the expert and should not be considered the university position on the issue. All publication content is subject to edits for clarity, brevity and university style guidelines.

With the United States government retiring its only Antarctic ice breaking ship, a CU Boulder researcher shares what's next for polar research.

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The Palmer in Barilari Bay, Antarctic Peninsula, January 1999. (Credit: Adam Jenkins/National Science Foundation)

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The Palmer in Barilari Bay, Antarctic Peninsula, January 1999. (Credit: Adam Jenkins/National Science Foundation)

The end of EV tax credits? An expert's take on what's at stake

Yvaine Ye — Thu, 11 Sep 2025 14:53:15 +0000

The end of EV tax credits? An expert's take on what's at stake Yvaine Ye Thu, 09/11/2025 - 08:53

Yvaine Ye

Electric vehicle sales in the United States are setting records. Over the past two months, consumers across the country have been rushing to car dealerships to buy EVs before a federal incentive providing up to $7,500 in tax credits ends Sept. 30.

In July, automakers sold more than 130,000 EVs, about 25% more than the month before. That number reached an all-time high in August, with about 12% of all new cars sold being electric.

The federal government rolled out current EV tax incentives in 2008, aiming to bridge the price difference between gasoline and electric cars. In 2022, the Inflation Reduction Act modified the policy by adding income caps for those eligible to receive the tax break and limiting the credit to EVs under a certain price. To qualify, vehicles also must be built in the United States using domestically sourced materials. This policy was set to run through 2032.

But in July, Congress approved the tax and spending legislation colloquially known as the Big Beautiful Bill, scrapping the discount seven years before its original expiration date.

“The move is broadly reflective of the government not wanting to promote electric vehicle adoption or environmental policy more generally,” said Stephanie Weber, assistant professor in the Department of Economics, noting that several other pro-EV policies have already been eliminated.

Stephanie Weber

As the program comes to an end, CU Boulder Today sat down with Weber, who is also a fellow at the Renewable and Sustainable Energy Institute, to discuss the impact federal incentives had and the outlook for electric cars.

Have the tax incentives for electric vehicles worked?

There’s evidence that a meaningful share, from 10% to 30%, of the EVs that were being sold were purchased because of the incentives.

Over the past 15 years, the types of products automakers offer in the United States have also improved. For example, we now have EVs with larger batteries that have more range before they need to be charged. We can attribute some of those improvements to the incentives. They motivate automakers to develop new products, knowing there’s this enhanced demand for EVs.

The current tax credit policy for EVs was set to expire in 2032. Doesn't that mean the government was going to phase out the incentives anyway?

The subsidies were always intended to be phased out. But from an economic perspective, some should maybe persist.

Economically, we want to use these incentives to solve what are called market failures—basically anything that causes us to deviate from efficient outcomes under a free market. In the case of vehicles, the major market failures are environmental impacts from gasoline vehicles, from local air pollution to greenhouse gas emissions.

Consumers, when they buy a car, don't necessarily have an incentive to consider the pollution impacts on other people. So we might want an ongoing incentive to push people into buying electric vehicles.

What happens now that the federal incentives are ending?

In the immediate term, we're seeing really big increases in electric vehicle adoption, because people want to make the purchase before the tax credit expires.

Over time, we will see a reduction in sales relative to what we’d see under the policy. It may not be an absolute decline in sales, although that's also possible, but it might be a flattening out in growth. Some estimates suggest that between 2026 and 2028, about 4% of new vehicles sold will be EVs, about half the current share, due to these policy changes.

How is this policy change affecting automakers?

We are going to see fewer new products than we might have otherwise. Some automakers have actually canceled EV models that they had previously announced. For example, Honda canceled plans for a large electric SUV in July, anticipating a decrease in U.S. demand. General Motors and Volkswagen have announced that they’re scaling back EV production. They are also going to spend less money trying to develop new electric vehicles and trying to improve the technology in the United States.

And it’s not just the tax credits that are getting taken away. There are other incentives on the automaker side for promoting EVs and fuel-efficient vehicles. Many of those have also been eliminated in the last year.

One was a waiver that allowed California to set its own vehicle emission rules, which were stricter than federal standards. The state mandated that a certain percent of new cars sold in California be zero-emission, ramping up to all new cars by 2035, and 11 other states, including Colorado, adopted California’s standards. They have also eliminated penalties for failing to meet Corporate Average Fuel Economy standards, which require automakers to sell more fuel-efficient vehicles, including electric vehicles.

What would be a better long-term policy than EV subsidies?

EV subsidies, as we've been doing them, are not the optimal policy, partly because these subsidies tend to disproportionately benefit wealthier people who can afford new vehicles.

From an economic standpoint, an effective environmental policy should align people's private incentives with societal incentives. So in this case, we would want to directly make it more expensive to generate pollution, through ways like putting a surcharge on gasoline.

Such a policy can have impacts beyond car-buying behaviors too. It would also make people consider things like, “Should I drive to the grocery store, or is this actually a small trip that I can make via the bus or bike?” and reduce their emissions that way. An EV subsidy isn't going to do that.

With federal incentives for electric vehicles ending in the United States this month, CU Boulder economist Stephanie Weber shares what's next for consumers and automakers.

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Electric car charging. (Credit: Andrew Roberts/Unsplash)

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As salmon disappear in warming rivers, Indigenous communities face an uncertain future

Yvaine Ye — Wed, 10 Sep 2025 20:24:27 +0000

As salmon disappear in warming rivers, Indigenous communities face an uncertain future Yvaine Ye Wed, 09/10/2025 - 14:24

Yvaine Ye

For millennia, Indigenous people living in Alaska and Canada’s Yukon territory have relied on Chinook salmon. The large, fatty fish provide essential nutrients for Arctic living and have influenced traditions and languages across generations.

But over the past three decades, many communities have been unable to fish Chinook amid a sharp salmon population decline.

The situation could worsen as climate change warms rivers in the Arctic, stunting salmon growth, according to a CU Boulder-led study published August 6 in Scientific Reports.

“The fish are really important for maintaining the culture and language of Indigenous communities,” said Peyton Thomas, a research associate at the Institute of Arctic and Alpine Research.

Peyton Thomas

In collaboration with locals on the ground, the team is now working to help communities prepare for the changes ahead.

Over the past two summers, Thomas and her team visited many Alaskan tribes to understand changes to the lands and communities.

“People pointed to not being able to teach their children the names of the fish or the practices of how to process them,” Thomas said.

The silver lining: Some rivers in the area could remain suitable for young salmon, and a less popular fish species, Dolly Varden, might benefit from warming waters.

Melting North Pole

Over the past 50 years, the Arctic has warmed nearly four times faster than the global average. Climate change has melted sea ice, thawed frozen ground and eroded coastlines, reshaping the Arctic landscapes Indigenous peoples have called home for generations.

In Alaska, Indigenous community members told Thomas that these changes have disrupted many aspects of their life: In winter, they haven’t been able to access neighboring villages, because the river connecting them didn’t freeze. Thinning and fragmented sea ice has made travel and hunting harder and riskier, cutting off sources of food and income. The area has seen more frequent and intense extreme weather events like typhoons, further damaging already limited infrastructure.

Prior research has suggested that increased river temperatures can affect fish species adapted to cooler environments. Chinook salmon in the Arctic are a prime example. These fish spend their first one to two years in cold river water bulking up, before embarking on a journey of hundreds of thousands of miles to the ocean. There, they spend the next six years growing, to up to 100 pounds, before returning to the rivers to spawn.

In recent decades, river communities in Alaska have seen a major decline in the number of young and adult salmon in the water. One study estimated that Chinook salmon populations in the Yukon River, Alaska’s largest, plummeted by more than 57% between 2003 and 2010.

When Thomas and team visited Indigenous tribes near the Alaska-Yukon border along the Yukon River, community members told them that they hadn’t been able to fish Chinook in 30 years.

“The loss of fish, as well as the loss of access to fishing and foraging grounds, means people are relying more on buying food from the store, which is really expensive and doesn’t meet their nutritional needs,” Thomas said.

Two fishes, two tales

Working closely with Indigenous communities in Alaska, Thomas and her team set out to better predict how climate change would affect fish populations in the seven river basins spanning watersheds in Alaska and Yukon.

After talking to tribal members, the team focused on two species important for subsistence, Chinook salmon and Dolly Varden, a type of trout.

Using computer models, the team simulated how the region’s climate and rivers might change by mid-century. They found that summer river temperatures could rise by 1.26 °C (2.27 °F) by mid-century compared to the average between 1990 and 2021.

When they combined these data with a fish growth model, they found that in the warmest future years, four out of seven river basins would experience water temperatures surging above what juvenile Chinook salmon can tolerate.

Rivers in Alaska are changing rapidly. (Credit: Peyton Thomas)

On the other hand, Dolly Varden thrive in slightly warmer water than Chinook salmon. The simulations suggested that these fish might nearly double their growth in many rivers.

“It is good news that not all species are going to decline under warming,” Thomas said. “But communities have different preferences about fishing Dolly Varden. We’re trying to show that maybe in warm years, Dolly Varden could be an alternative.”

The team also identified some rivers that may serve as refuges for Chinook. For example, the Aniak and Andreafsky rivers, both tributaries of the Yukon River in Alaska, are likely to remain suitable habitats. Protecting and restoring juvenile salmon in these rivers could bring the greatest benefit, Thomas said.

“We are hoping to provide communities with some applicable information, like when and where the water would be too warm for salmon, which could help them decide whether to reduce fishing,” she said.

Uncertain future

This study comes just a year after Alaska and Canadian authorities agreed to pause Chinook salmon fishing, both commercial and subsistence, for seven years in a bid to allow their populations to recover.

The fishing ban only applies to Canadian-origin Chinook. Commercial fishing continues for the Alaska stock.

“Everything has an impact on fish populations. We need more studies to look into not just the environmental factors, but also how fishing activities play a role,” Thomas said.

Wild Fish Conservancy, a nonprofit conservation group, has filed a petition with the National Oceanic and Atmospheric Administration (NOAA) to have Alaska Chinook salmon receive federal protection under the Endangered Species Act, which would ban commercial fishing of this species. The decision is still pending.

Meanwhile, Thomas plans to return to Alaska next year.

“The coolest part of this work is just being able to see how we're all trying to connect with each other,” Thomas said. “We learned so much from history and people's daily lived experiences in these places. Everyone should be a part of all of this work, because we can't do it just by modeling.”

New research shows that climate change is exacerbating salmon declines in the Arctic, but warming waters could give another fish species a temporary boost.

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Yukon-Charley Rivers National Preserve in Alasaka. (Credit: Alaska National Park Service/Flickr)

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Yukon-Charley Rivers National Preserve in Alasaka. (Credit: Alaska National Park Service/Flickr)

Katrina 20 years later: What we've learned

Lisa Marshall — Fri, 29 Aug 2025 18:05:21 +0000

Katrina 20 years later: What we've learned Lisa Marshall Fri, 08/29/2025 - 12:05

Lisa Marshall

Driving into New Orleans two weeks after Hurricane Katrina made landfall, Lori Peek was overcome with sorrow.

Lori Peek stands near the Lower Ninth Ward in New Orleans prior to the 10th anniversary of Hurricane Katrina. Credit: Charles Varley

Trees were flattened for miles. Water marks up to 20 feet high blackened apartment buildings. Holes in rooftops revealed where desperate families had used axes to try to escape the rising floods.

“You looked up at these houses, and you just had to pause and be silent,” recalled Peek, who just months before Katrina’s landfall had earned her doctorate in sociology from CU Boulder.

Weeks after the storm, she traveled to Louisiana to begin a collaborative study of Katrina’s impacts on children. “Not knowing if these people had survived, or what had happened to the children and their parents...these are images I will never forget.”

Twenty years later, Peek has co-authored three books and nearly 20 research papers about the historic storm, which killed more than 1,800 people, displaced an estimated 1.2 million residents from the Gulf Coast, and separated 5,000 children from their families.

Now, as director of CU’s Natural Hazards Center and professor of sociology, she views Katrina as a “pivotal turning point” for the country. It not only revealed what’s possible—meteorologically—amid a warming climate, she said, but it also pulled back the curtain on social inequities that make some populations more vulnerable to natural hazards.

Nearly 20 years after Katrina, CU Boulder Today caught up with Peek to discuss what the disaster taught us—and what we have yet to learn.

What was unique about Katrina?

A New Orleans resident seeks shelter on a rooftop during Hurricane Katrina. Credit: Charles Varley

The storm itself was a monster. Even though it was only a Category 3 when it made its second landfall in Louisiana on Aug. 29, 2005, it was at one point a Category 5 and, at that time, one of the most intense Atlantic hurricanes ever recorded.

We’re still talking about Katrina 20 years later, though, not because of its meteorological properties, but due to the social impacts. This was the first time in New Orleans history that the city was placed under a mandatory evacuation order. It was the first major natural disaster that was captured in a 24-hour news cycle, so people's immense suffering was on full display. It starkly revealed inequalities along race, class, gender and age lines.

How so?

People were told they were supposed to leave New Orleans, but at least 100,000 did not, and research has revealed that in most cases, they didn’t evacuate because they didn't have the resources.

It was the end of the month, and many people reported they didn't have money for gas or they didn't have a car. Others were caring for elders or children. New Orleans also had one of the highest disability rates in the country, and some couldn’t get access to transportation or couldn’t leave without their caregiver.

At the end of the day, the images that people saw on TV were overwhelmingly of Black Americans, low-income Americans, children, people with disabilities and elders suffering. People were stuck on rooftops in sweltering heat or wading through toxic floodwaters. Thousands ended up in so-called “refuges of last resort”—like the Superdome or Convention Center, which were not meant to house that many people for a week.

Were certain groups more likely to perish?

Yes. Even though people over age 65 only made up about 12% of the population of New Orleans, they made up 67% of those who died.

What happened in the months and years after the storm?

At one point, data indicated that Katrina survivors landed in every single state in the nation, and even in every county in Colorado. But when you look at who was displaced the farthest and who was or was not able to return, it, again, revealed how pre-existing inequalities shape people’s recovery.

Even 10 years after Katrina, data showed that low-income people, Black residents, single mothers and people with disabilities were least likely to be able to return home. It’s important to say that these survivors were not passive. Much research documented the incredible ingenuity and strength of families that worked tirelessly to rebuild their lives after the catastrophe.

What about the children?

Of the 5,000 children separated from their caregivers during the chaos of Katrina, the last child was not reunited with her family until April of 2006—more than six months after the storm. Even two years after, one study showed that some 160,000 children were still displaced from their home school district and not back into stable education and housing.

The boys and girls who we followed for nearly a decade for our book, "Children of Katrina," experienced loss of community and separation of family, but they also were generous and creative as they worked to contribute to the recovery.

New Orleans residents line up outside the Louisiana Superdome, seeking shelter, after Hurrican Katrina left much of the city underwater.

What changes resulted from Katrina?

It was a reckoning for the emergency management community.

The former head of the Federal Emergency Management Agency was fired in the midst of the disaster, and, later, the government accepted responsibility for the failures that occurred at multiple levels.

In response, the emergency management community, nationwide, began to update their planning guidance to take much more careful account of vulnerable populations and better plan for the whole community.

This was a wake-up call for personnel in other countries, too. They were surprised that something like this could happen in the United States.

Learn more

Learn more

The Natural Hazards Center will host a webinar, Hurricane Katrina at 20: Looking Back and Moving Forward, at 11 a.m. Friday, Aug. 29.

Could it happen again today?

Absolutely. Meteorologists have obviously recorded even bigger and more rapidly intensifying storms since. More people live in coastal areas now. And because we're also seeing rising economic inequality, we have more people without the means to take recommended preparedness actions.

We’ve also had a rollback of hazard mitigation and preparedness planning grants and initiatives recently and a loss of many of our federal officials who have been most responsible for leading mitigation and preparedness. This leaves us more exposed and vulnerable at a time when the risk of severe storms is rising.

What advice do you have, as we reflect on this somber anniversary?

Go back and look at the images from Katrina. Look at the city of New Orleans, a vital city, underwater, but then home in and look at those people's faces. Know that there were actions that could have been taken in advance to lessen the suffering.

There are all kinds of lessons to be learned, but we're running out of time. The next disaster is right around the corner.

On Aug. 29, 2005, Hurricane Katrina tore through New Orleans, killing more than 1,800 people and displacing 1.2 million. Natural Hazards Center Director Lori Peek reflects on what we learned—or should have.

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New research paves way for greener construction practices

Megan Maneval — Tue, 19 Aug 2025 19:46:00 +0000

New research paves way for greener construction practices Megan Maneval Tue, 08/19/2025 - 13:46

College of Engineering and Applied Science

A study led by doctoral student Daniel Donado-Quintero shows that setting carbon benchmarks can encourage asphalt producers to lower emissions and optimize production processes—supporting Colorado’s Buy Clean Act and other efforts.

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