In the century since their conception, people have come to understand the enormous impacts – beneficial as well as detrimental – plastics have on human lives and the environment. As a group of polymer scientists dedicated to inventing sustainable solutions for real-world problems, we set out to tackle this issue by rethinking the way polymers are designed and making plastics with recyclability built right in.

Why use plastics, anyway?

Everyday items including milk jugs, grocery bags, takeout containers and even ropes are made from a class of polymers called polyolefins. Polyolefins make up around half of the plastics produced and disposed of every year.

These polymers are used in plastics commonly labeled as HDPE, LLDPE or PP, or by their recycling codes #2, #4 and #5, respectively. These plastics are incredibly durable because the chemical bonds that make them up are extremely stable. But in a world set up for single-use consumption, this is no longer a design feature but rather a design flaw.

Imagine if half of the plastics used today were recyclable by twice as many processes as they are now. While that wouldn’t get the recycling rate to 100%, a jump from single digits – currently around 9% – to double digits would make a big dent in the plastics produced, the plastics accumulated in the environment and their capacity for recycling and reuse.

Recycling methods we already have

Even the plastics that make it to a recycling facility can’t be reused in exactly the same way they were used before – the recycling process degrades the material, so it loses utility and value. Instead of making a plastic cup that is downgraded each time it gets recycled, manufacturers could potentially make plastics once, collect them and reuse them on and on.

Conventional recycling requires careful sorting of all the collected materials, which can be hard with so many different plastics. Here in the U.S., collection happens mainly through single stream recycling – everything from metal cans, glass bottles, cardboard boxes and plastic cups end up in the same bin. Separating paper from metal doesn’t require complex technology, but sorting a polypropylene container from a polyethylene milk jug is hard to do without the occasional mistake.

When two different plastics are mixed together during recycling, their useful properties are hugely reduced – to the point of making them useless.

But say you can recycle one of these plastics by a different method, so it doesn’t end up contaminating the recycling stream. When we mixed samples of polypropylene with a polymer we made, we were still able to depolymerize – or break down the material – and regain our building blocks without chemically affecting the polypropylene. This indicated that a contaminated waste stream could still recover its value, and the material in it could go on to be recycled, either mechanically or chemically.

Plastics we need − but more recyclable

In a study published in October 2023, our team developed a series of polymers with only two simple building blocks – one soft polymer and one hard polymer – that mimicked polyolefins but could also be chemically recycled.

Connecting two different polymers together multiple times until they form a single, long molecule creates what’s called a multiblock polymer. Just by adjusting how much of each polymer type goes into the multiblock polymer, our team created a wide range of materials with properties that spanned across polyolefin types. But creating these multiblock polymers is easier said than done.

To link these hard and soft polymers, we adapted a technique that had previously been used only on very small molecules. This method is improved relative to traditional methods of making polymers in a step-by-step fashion, developed in the 1920s, where the reactive groups on the end of the molecules need to be exactly matched.

In our method, the reactive groups are now the same as each other, meaning we didn’t have to worry about pairing the ends of each building block to make polymers that can compete with the polyolefins we already use. Using the same strategy, applied in reverse by adding hydrogen, we could disconnect the polymers back into their building blocks and easily separate them to use again.

With an almost twofold increase in annual plastic use projected through 2050, the complexity and quantity of plastic recycling will only increase. It’s an important consideration when designing new materials and products.

Using just two building blocks to make plastics that have a huge variety of properties can go a long way toward reducing and streamlining the number of different plastics used to make the products we need. Instead of needing one plastic to make something pliable, another for something stiff, and a third, fourth and fifth for properties in between, we could control the behavior of plastics by just changing how much of each building block is there.

Although we’re still in the process of answering some big questions about these polymers, we believe this work is a step in the right direction toward more sustainable plastics.

We were able to create materials that mimic the properties of plastics the world relies on, and our sights are now set on creating plastic compositions that you couldn’t with existing methods.

A primary aim of this year’s conference, known as COP28, is to evaluate countries’ progress halfway to the 2030 deadlines.

Reports show that the world isn’t on track. At the same time, energy security concerns and disputes over how to compensate countries for loss and damage from climate change are making agreements on cutting emissions tougher to reach.

But as energy and environmental policy researchers, we also see signs of progress.

Global stocktake raises alarms

A cornerstone of COP28 is the conclusion of the global stocktake, a review underway of the world’s efforts to address climate change. It is designed to pinpoint deficiencies and help countries recalibrate their climate strategies.

A report on the stocktake so far stressed that while the Paris Agreement has spurred action on climate change around the globe, current policies and promises to cut greenhouse gas emissions still leave the world on a trajectory that falls far short of the agreement’s aim to limit warming to less than 1.5 degrees Celsius (2.7 Fahrenheit) compared with preindustrial temperatures.

If countries meet their current pledges, the world is likely to warm by about 2.5 C (4.5 F) by the end of this century, the U.N. warned in late November. And countries’ current policies put warming closer to 3 C (5.4 F), the U.N.‘s Emissions Gap Report shows.

Those temperature difference might seem minor, but the accumulated global benefits of limiting warming to 1.5 C (2.7 F) rather than 2 C (3.6 F) could exceed US$20 trillion.

Escalating greenhouse gas emissions are the primary factor driving the rise in global temperatures. Fossil fuels account for over three-quarters of those emissions, and data show governments worldwide plan to produce twice as much fossil fuel in 2030 than would be allowed under a 1.5 C warming pathway.

To avoid overshooting 1.5 C of warming, global greenhouse gas emissions will have to fall by about 45% by 2030, compared with 2010 levels, and reach net zero around 2050, according to the Intergovernmental Panel on Climate Change.

But emissions aren’t falling. They rose in 2022, surpassing pre-pandemic levels. The global average temperature briefly breached the 1.5 C warming limit in March and June 2023.

The global stocktake unambiguously states that, to meet the Paris targets, countries must collectively be more ambitious in cutting greenhouse gas emissions. That includes rapidly reducing carbon emissions from all economic sectors. It means accelerating adoption of renewable energy such as solar and wind power, implementing more stringent measures to stop and reverse deforestation, and deploying clean technologies such as heat pumps and electric vehicles on a wide scale.

The significance of phasing out fossil fuels

The report underscores one point repeatedly: the pressing need to “phase out all unabated fossil fuels.”

Fossil fuels currently make up 80% of the world’s total energy consumption. Their use in 2022 resulted in an all-time high of 36.8 gigatons of CO2 from both energy combustion and industrial activities.

Despite the risks of climate change, countries still provide huge subsidies to the oil, coal and gas industries. In all, they provided about US$1.3 trillion in explicit subsidies for fossil fuels in 2022, according to the International Monetary Fund’s calculations. China, the U.S., Russia, the European Union and India are the largest subsidizers, and these subsidies sharply increased after Russia’s invasion of Ukraine in 2022 disrupted energy markets.

U.N. Secretary-General António Guterres has stressed the importance of transitioning away from fossil fuels, criticizing the extensive profits made by “entrenched interests” in the fossil fuel sector.

African countries also made their view of subsidies clear in the “Nairobi Declaration” at the first Africa Climate Summit in 2023, where leaders called for the elimination of inefficient fossil fuel subsidies and endorsed the idea of a global carbon tax on fossil fuel trade.

The global stocktake highlights the significance of eradicating fossil fuel subsidies to eliminate economic roadblocks that hinder the shift to greener energy sources. However, it’s important to note that the report uses the phrase “unabated fossil fuels.” The word “unabated” has been contentious. It allows room for continued use of fossil fuels, as long as technologies such as carbon capture and storage prevent emissions from entering the atmosphere. But those technologies aren’t yet operating on a wide scale.

Solutions for an equitable transition

Several initiatives have been launched recently to expedite the move away from fossil fuels.

In July 2023, Canada unveiled a strategy to terminate inefficient fossil fuel subsidies, becoming the first G20 nation to pledge a halt to government support for oil and natural gas, with some exceptions.

The European Union is broadening its carbon market to include emissions from buildings and transport, targeting decarbonization across more sectors. Concurrently, the United States’ Inflation Reduction Act commits US$10 billion to clean energy projects and offers $4 billion in tax credits to communities economically affected by the coal industry’s decline.

To help low-income countries build sustainable energy infrastructure, a relatively new financing mechanism called Just Energy Transition Partnerships is gaining interest. It aims to facilitate cooperation, with a group of developed countries helping phase out coal in developing economies that are still reliant on fossil fuels.

South Africa, Indonesia, Senegal and Vietnam have benefited from these partnerships since the first was launched in 2021. The European Union, for instance, has pledged to support Senegal’s shift from fossil fuels to renewable energy. This includes managing the economic fallout, such as potential job losses, from shutting down fossil fuel power plants, while ensuring electricity remains affordable and more widely available.

By COP28, a comprehensive plan to help Senegal aim for a sustainable, low-emissions future should be in place. France, Germany, Canada and various multilateral development banks have promised to provide 2.5 billion Euros (about US$2.68 billion) to increase Senegal’s renewable energy output. The goal is for renewables to account for 40% of Senegal’s energy use by 2030.

To align with the Paris Agreement objectives, we believe global initiatives to reduce fossil fuel dependency and invest in developing nations’ sustainable energy transition are essential. Such endeavors not only champion reducing greenhouse gas emissions but also ensure economic growth in an environmentally conscious manner.

Animal nervous systems play a central role in both enabling and limiting how they respond to changing climates. Two of my main research interests as a biologist and neuroscientist involve understanding how animals accommodate temperature extremes and identifying the forces that shape the structure and function of animal nervous systems, especially brains. The intersection of these interests led me to explore the effects of climate on nervous systems and how animals will likely respond to rapidly shifting environments.

All major functions of the nervous system – sense detection, mental processing and behavior direction – are critical. They allow animals to navigate their environments in ways that enable their survival and reproduction. Climate change will likely affect these functions, often for the worse.

Shifting sensory environments

Changing temperatures shift the energy balance of ecosystems – from plants that produce energy from sunlight to the animals that consume plants and other animals – subsequently altering the sensory worlds that animals experience. It is likely that climate change will challenge all of their senses, from sight and taste to smell and touch.

Animals like mammals perceive temperature in part with special receptor proteins in their nervous systems that respond to heat and cold, discriminating between moderate and extreme temperatures. These receptor proteins help animals seek appropriate habitats and may play a critical role in how animals respond to changing temperatures.

Climate change disrupts the environmental cues animals rely on to solve problems like selecting a habitat, finding food and choosing mates. Some animals, such as mosquitoes that transmit parasites and pathogens, rely on temperature gradients to orient themselves to their environment. Temperature shifts are altering where and when mosquitoes search for hosts, leading to changes in disease transmission.

How climate change affects the chemical signals animals use to communicate with each other or harm competitors can be especially complex because chemical compounds are highly sensitive to temperature.

Formerly reliable sources of information like seasonal changes in daylight can lose its utility as they become uncoupled. This could cause a breakdown in the link between day length and plant flowering and fruiting, and interruptions to animal behavior like hibernation and migration when day length no longer predicts resource availability.

Changing brains and cognition

Rising temperatures may disrupt how animal brains develop and function, with potentially negative effects on their ability to effectively adapt to their new environments.

Researchers have documented how temperature extremes can alter individual neurons at the genetic and structural levels, as well as how the brain is organized as a whole.

In marine environments, researchers have found that climate-induced changes of water chemistry like ocean acidification can affect animals’ general cognitive performance and sensory abilities, such as odor tracking in reef fish and sharks.

Behavior disruptions

Animals may respond to climate adversity by shifting locations, from changing the microhabitats they use to altering their geographic ranges.

Activity can also shift to different periods of the day or to new seasons. These behavioral responses can have major implications for the environmental stimuli animals will be exposed to.

For example, fish in warming seas have shifted to cooler, deeper waters that have dramatically different light intensity and color range than their visual systems are used to. Furthermore, because not all species will shift their behaviors in the same way, species that do move to a new habitat, time of day or season will confront new ones, including food plants and prey animals, competitors and predators, and pathogens.

Behavioral shifts driven by climate change will restructure ecosystems worldwide, with complex and unpredictable outcomes.

Plasticity and evolution

Animal brains are remarkably flexible, developed to match individual environmental experience. They’re even substantially capable of changing in adulthood.

But studies comparing species have seen strong environmental effects on brain evolution. Animal nervous systems evolve to match the sensory environments of each species’ activity space. These patterns suggest that new climate regimes will eventually shape nervous systems by forcing them to evolve.

When genetics have strong effects on brain development, nervous systems that are finely adapted to the local environment may lose their adaptive edge with climate change. This may pave the way for new adaptive solutions. As the range and significance of sensory stimuli and seasonal cues shift, natural selection will favor those with new sensory or cognitive abilities.

Some parts of the nervous system are constrained by genetic adaptations while others are more plastic and responsive to environmental conditions. A greater understanding of how animal nervous systems adapt to rapidly changing environments will help predict how all species will be affected by climate change.

Because such deprivation dramatically affects the well-being of people who are homeless, public discussion of homelessness tends to focus on whether and to what extent the government should carry out anti-homelessness policy as a way of improving people’s overall quality of life.

Some philosophers have argued that while homelessness is clearly a state of deprivation, it is also a condition in which a person’s freedom is profoundly compromised.

These theorists insist a society that cherishes freedom – such as the U.S. – must implement anti-homelessness policy as a way of liberating people who lack housing.

Because the number of people experiencing homelessness continues to rise at a record rate, these academic ideas have become increasingly relevant to the real world. I am a philosopher interested in exploring the moral dimensions of homelessness, as well as shining a light on underdiscussed aspects of it. I believe that public debate would benefit greatly from increased attention to the ways homelessness limits Americans’ freedom.

Freedom to be somewhere

Since homelessness is usually discussed in terms of deprivation, the claim that homelessness has much to do with freedom can seem surprising.

Freedom is commonly understood as the ability to do what one chooses without being interfered with. My freedom is limited if you lock me in a cell or place a boulder on the street I want to drive down.

Homelessness, on the other hand, seems at first glance like a condition in which a person is mostly able to do as they choose, albeit without important resources that would make their life better.

The philosopher and legal theorist Jeremy Waldron sees things differently. Waldron says that private property often serves to interfere with people’s choices. If a person wants to walk in New York City from midtown Manhattan to Harlem, others’ property interferes with their ability to choose the most direct route. If a person wants to see a particular Andy Warhol painting, the fact that it is kept at a private residence interferes with their ability to choose to view it.

In itself, this isn’t a problem, as no one should be free to go anywhere and do anything they want. The trouble, says Waldron, comes when a person who is homeless does not have private property that they are able to occupy, free from interference. In such instances, the person will be confined to public spaces, such as sidewalks and parks.

But public spaces themselves are highly regulated through local ordinances, limiting who may use them and for what purposes.

A person who is homeless and sleeps on a public bench will often be told by the police to move. Someone who sets up a tent on a sidewalk will usually have it confiscated. Someone who urinates or defecates in a park can be arrested.

Now you can see why some think that homelessness compromises a person’s freedom. Sleeping and relieving oneself are necessary, life-sustaining tasks.

But as Waldron points out, “Everything that is done has to be done somewhere. No one is free to perform an action unless there is somewhere he is free to perform it.”

Given the way society protects private property and regulates public spaces, it seems that people who are homeless are left with no space at all in which they are free to do the things they need to do in order to live. This is about as severe an infringement on freedom as you can imagine, and Waldron’s point is that a society that loves freedom simply cannot tolerate it.

Anti-homelessness is not just about benevolence and generosity, then. It is about protecting liberty.

Freedom from others

Of course, people who are homeless do sleep and relieve themselves. So, in what sense do they actually lack the freedom to do so?

The political philosopher Christopher Essert argues that Waldron’s analysis should be taken one step further by considering its implications for interpersonal relations.

Since a person who is homeless has nowhere to freely perform life-sustaining tasks, typically they will either seek permission from someone to use their property, use the property and hope to not be noticed or, at worst, seek forgiveness. Either way, they depend upon the grace of another in order to do the things they need to do.

This puts people who are homeless at the mercy of those who have property.

Whether a homeless person has a place to sleep or whether they are arrested for sleeping somewhere without permission is completely determined by the wishes of others. Keesha might sleep on Felix’s couch for a few nights. But as soon as Felix is in a bad mood, he can throw her out. Or Felix might make access to his couch conditional upon her attending church services, supporting his preferred political candidate or performing sexual acts. What she does and does not do is now up to Felix.

Essert connects this set of observations to what is called a “republican” conception of freedom. This way of understanding freedom is less about whether a person is actually interfered with and more about the way they are placed under the arbitrary power of another.

The intuitive idea is that if someone else always has the power to determine your choices, then you aren’t free. Since a homeless person is always on property over which someone else has authority, they are always, writes Essert, “under the power of others, dependent on them, dominated by them, unfree.”

In the U.S. especially, arguments that appeal to freedom are taken very seriously. Even those who insist that it is not the government’s job to ensure everyone a good quality of life believe that it must ensure freedom. Even those whose ears close when they hear calls for charity and beneficence seem to pay attention when freedom is at stake.

By proposing this way of seeing the life of someone who is homeless, then, philosophers have raised the possibility that allowing homelessness to persist contradicts values that are, at heart, fundamentally American.

In 2022, 420 people – many of them unsheltered – died in Phoenix from heat-related causes. Estimates are not yet available for summer 2023, but given this year’s extreme conditions, the toll is expected to be higher.

For the past two years, we have worked as researchers with the Human Services Campus, a 13-acre complex in Maricopa County, Arizona, where 16 nonprofit organizations work together to help people who are experiencing homelessness. The campus includes Central Arizona Shelter Services, or CASS, Phoenix’s largest homeless emergency shelter, which assists 800 people experiencing homelessness on any given night.

Our work includes talking with staff and clients to better understand their challenges and identify possible solutions that draw from our work in the fields of architecture, health and social innovation.

Dormitories at CASS protect residents from extreme heat with a bunk to sleep in, day rooms for socializing, case management services, and sanitary shower and restroom facilities. But CASS struggles to provide dignified spaces that offer privacy, storage space and quiet environments. People need this kind of environmental support in order to battle recurring physical and mental health issues that often accompany homelessness and can hinder or prevent healing.

Overflowing shelters

As of 2022, the U.S. Department of Housing and Urban Development estimated that the U.S. had nearly 600,000 homeless people nationwide, with about 60% living in emergency shelters, safe havens or transitional housing. The other 40% lived outdoors or in places such as abandoned buildings and public transit stations.

Homeless centers must conform to architectural standards for emergency shelter. These standards have historically been influenced by institutional building design, which prioritizes attaining minimum conditions needed to keep people alive. Today, many homeless shelters struggle to provide even that level of care.

The Human Services Campus was originally constructed in 2003 to provide consolidated services and a coordinated entry plan for people experiencing homelessness. However, it was intended to be part of a larger system of shelters, not the sole service provider for Phoenix’s estimated 9,000 homeless people.

The city’s homeless population has grown, in part because of unprecedented rent increases and a lack of affordable housing. During this summer’s heat wave, nearly 1,200 unsheltered homeless people lived on sidewalks surrounding the campus, many in tents, with limited access to bathrooms and sanitation facilities.

Homelessness and mental health

When asked about causes of homelessness, policymakers and members of the public often point to mental illness and addiction, as well as a lack of affordable housing. They tend to pay less attention to the underlying impacts of past trauma other than noting that many women become homeless to escape domestic violence.

In a 2005 study, an alarming 79% of homeless women seeking treatment for mental illness and substance abuse reported experiencing a past traumatic event such as physical or sexual abuse. More recently, a 2020 study showed that nearly two-thirds of homeless women and almost half of homeless men reported that they were homeless because of trauma. Shelter design can affect homeless people’s ability to recover from past trauma and to battle addiction and other mental health issues that perpetuate cycles of homelessness.

For example, one woman who currently lives in CASS told us about trying to get a full night’s sleep while living in a day room where the lights were kept on around the clock and there was constant activity. Because she had several bags of personal items that were too big to store in the dormitory, she could not get a bed there.

“When they don’t turn the lights down at night, I start to feel like my body is vibrating,” she said. “I start to see people walking around, and I’m not sure if they are even really there.”

Routinely sleeping less than seven hours per night can be harmful to health. It lowers immune function, increases chronic pain and raises the risk of heart disease, high blood pressure, diabetes, stroke and death. For homeless people battling mental health challenges, addiction and past trauma, rest and recovery are essential to getting back on their feet.

CASS staff have tried to create healthier sleep spaces, such as dorms that remain dark, quiet and cool at all times. Priority access goes to people with jobs. These sections can house only about a third of CASS’s residents, leaving others to sleep in dorms where there is more noise and light.

More supportive spaces

Simply feeding people and providing them with places to sleep is a major challenge for shelters in cities where homelessness is rising. But some have found ways to think more broadly.

In San Diego, Father Joe’s Villages, a nonprofit network with a central campus and scattered-site programs, houses more than 2,000 people nightly. San Diego’s more temperate climate makes it less urgent to maximize the number of people they shelter indoors, so staff at Father Joe’s can use its decentralized design to create shelters with private and quiet spaces.

The Father Joe’s network includes multiple smaller-scale facilities where clean bathrooms are easily accessible and homeless people can use basic amenities like laundry and storage. One example is Mary’s Place, a collection of diverse shelters that provides emergency and long-term support in smaller facilities modeled after the simplicity and comfort of a home.

People experience less stress and can more easily navigate the challenge of ending their own homelessness when they can get a restful night’s sleep in a quiet environment, with spaces that allow them some privacy. We are encouraged to see other U.S. shelters moving in this direction – but there’s a long way to go.

Steps toward better design

To address the lack of privacy at CASS, we have proposed subdividing the day room into more private spaces to accommodate activities like online telehealth appointments, counseling and job interviews. To tackle long-term impacts of overcrowding, we also have recommended introducing sanitation amenities, such as laundry facilities, “hot boxes” to sanitize clothing and bedding, more bathroom facilities and reliable trash removal to reduce the spread of infection and pests such as bedbugs and lice.

For new facilities, designers could consider small changes, such as increased storage and more diligent regulation of temperature, light and noise.

Hospitals, nursing homes and retirement communities have found many ways in recent decades to use design to support patients’ health. Many of the same concepts can be applied to emergency shelters and help turn these facilities from institutional warehouses into spaces of health and opportunity.

Getting rid of these gases isn’t as simple as turning on an air purifier or opening a window on a clear day.

In a new study published in the journal Science Advances, colleagues and I tracked the life of these gases in a home exposed to wildfire smoke. We also found that the best way to get rid of the risk is among the simplest: start cleaning.

The challenge of smoke particles and gases

In December 2021, several of my friends and colleagues were affected by the Marshall Fire that burned about 1,000 homes in Boulder County, Colorado. The “lucky” ones, whose homes were still standing, asked me what they should do to clean their houses. I am an atmospheric and indoor chemist, so I started looking into the published research, but I found very few studies on what happens after a building is exposed to smoke.

What scientists did know was that smoke particles end up on indoor surfaces – floors, walls, ceilings. We knew that air filters could remove particles from the air. And colleagues and I were just beginning to understand that volatile organic compounds, which are traditionally thought to stay in the air, could actually stick to surfaces inside a home and build up reservoirs – invisible pools of organic molecules that can contribute to the air chemistry inside the house.

Volatile organic compounds, or VOCs, are compounds that easily become gases at room temperature. They include everything from limonene in lemons to benzene in gasoline. VOCs aren’t always hazardous to human health, but many VOCs in smoke are. I started to wonder whether the VOCs in wildfire smoke could also stick to the surfaces of a house.

Tracking lingering risks in a test house

I worked with researchers from across the U.S. and Canada to explore this problem during the Chemical Assessment of Surfaces and Air, or CASA, study in 2022. We built on HOMEChem, a previous study in which we looked at how cooking, cleaning and occupancy could change indoor air.

In CASA, we studied what happens when pollutants and chemicals get inside our homes – pesticides, smog and even wood smoke.

Using a cocktail smoker and wood chips, we created a surprisingly chemically accurate proxy for wildfire smoke and released small doses into a test house built by the National Institute of Standards and Technology. NIST’s house allowed us to conduct controlled chemistry experiments in a real-world setting.

We even aged the smoke in a large bag with ozone to simulate what happens when smoke travels long distances, like the smoke from Canadian wildfires that moved into the U.S. in the summer of 2023. Smoke chemistry changes as it travels: Particles become more oxidized and brown, while VOCs break down and the smoke loses its distinctive smell.

How VOCs behave in your home

What we found in CASA was intriguing. While smoke particles quickly settled on indoor surfaces, VOCs were more insidious.

At first, the house took up these smoke VOCs – on floors, walls and building surfaces. But once the initial smoke cleared, the house would slowly release those VOCs back out over the next hours, days or even months, depending on the type of VOC.

This release is what we call a partitioning process: During the smoke event, individual VOC molecules in the air attach to indoor surfaces with weak chemical bonds. The process is called adsorption. As smoke clears and the air cleans out, the bonds can break, and molecules “desorb” back out into the air.

We could watch this partitioning happen in the air by measuring smoke VOC concentrations. On surfaces, we could measure the weight of smoke VOCs that deposited on very sensitive balances and then were slowly released.

Overall, we concluded that this surface reservoir allows smoke VOCs to linger indoors, meaning that people are exposed to them not just during the major smoke event but also long after.

Why worry about VOCs?

Smoke VOCs include well-known carcinogens, and high levels of exposure can induce respiratory and health problems.

While smoke VOC concentrations in our test house decreased with time, they remained persistently elevated above normal levels.

Given that VOC concentrations from other sources, such as cooking and cleaning, can already be high enough in homes to harm health, this additional long-term exposure source from smoke could be important. Further toxicology studies will be needed to determine the significance of its health effects.

How to clean up when smoke gets in

So, what can you do to remove these lingering smoke gases?

We found that air purifiers can remove only some of the VOCs that are in the air – they can’t clean the VOCs on your floors or in your walls. They also work only when they’re running, and even then, air purifiers don’t work particularly well to reduce VOCs.

Opening windows to ventilate will clean the air, if it isn’t smoggy or smoky outside. But as soon as we closed windows and doors, smoke VOCs started to bleed off the surface reservoirs and into the air again, resulting in an elevated, near-constant concentration.

We realized that to permanently remove those smoke VOCs, we had to physically remove them from surfaces.

The good news is that cleaning surfaces by vacuuming, dusting and mopping with a commercial, nonbleach solution did the trick. While some remediation companies may do this surface cleaning for you after extreme exposures, surface cleaning after any smoke event – like Canadian wildfire smoke drifting into homes in 2023 – should effectively and permanently reduced smoke VOC levels indoors.

Of course, we could reach only a certain number of surfaces – it’s hard to vacuum the ceiling! That meant that surface cleaning improved but didn’t eliminate smoke VOC levels in the house. But our study at least provides a path forward for cleaning indoor spaces affected by air pollutants, whether from wildfires, chemical spills or other events.

With wildfires becoming more frequent, surface cleaning can be an easy, cheap and effective way to improve indoor air quality.

Sea ice, according to scientists, is melting at an alarming rate—so quickly that some researchers believe traditional methods for forecasting its extent may not keep up with the pace of a changing climate. 

By the year 2050, the Arctic could be ice-free in the summer months. And shipping traffic in the region is on the rise, but predicting sea ice extent is complicated. 

Today we’re looking at how machine learning—artificial intelligence—could become the tool of the future for sea ice forecasting. 

Leslie Canavera: We build artificial intelligence and machine learning models for the Arctic, based on the science of oceanography.

Schwing: That’s Leslie Canavera. She is CEO of a company called PolArctic, and she is trying to forecast ice in a different way than science ever has.

Since the late 1970s, scientists have relied on physics and statistical modeling to create sea ice forecasts. 

Canavera: When you take two water molecules, and you freeze them together, you know, like, right, this is how they freeze together. But there’s a lot of assumptions in that. And when you extrapolate to the ocean, there’s a lot of error.... And statistical modeling is based on, like, historical things of what’s happened. But with climate change, it’s not acting like the history anymore. And so artificial intelligence really takes the best of both of those and is able to learn the system and trends to be able to forecast that more accurately.

Schwing: Of course, that foundation of statistics and historical data is still important, even with its errors and caveats. 

Holland: We can't model every centimeter of the globe.

Schwing: Marika Holland is a scientist at the National Center for Atmospheric Research in Boulder, Colorado. The center has been using physics and statistical modeling to predict sea ice extent for the past five decades. Holland says that she is confident in the methodology but that these forecasts aren’t perfect.  

Holland: You know, we have to kind of coarsen things, and so we get a little bit of a muddy picture of how the sea ice cover is changing or how aspects of the climate or the Earth’s system are evolving over time. 

Schwing: Marika says there are also a lot of smaller-scale processes that can create problems for accurate forecasting.

Holland: Something like the snow cover on the sea ice, which can be really heterogeneous, and that snow is really insulating, it can affect how much heat gets through the ice.... We have to approximate those things because we aren’t going to resolve every centimeter of snow on the sea ice, for example.... So there’s always room for improvement in these systems.

Schwing: It’s that space—the room for improvement—where Leslie says artificial intelligence can be most helpful. And that help is especially important right now because of what is happening in the Arctic.

According to the Arctic Council, marine traffic increased by 44 percent through the Northwest Passage between 2013 and 2019. Search-and-rescue capabilities in the region are limited, and there has been increased attention on the region for its vast natural resource development potential. Leslie says AI can create a forecast on a smaller scale, homing in on specific locations and timing to benefit those user groups.

Canavera : We did a seasonal forecast and then an operational forecast where the seasonal forecast was 13 weeks in advance. We were able to forecast when their route would be open..., and we were actually to the day on when the route would be able to be open and they would be able to go. And then we did operational forecasts where it was like,“All right, you’re in the route, what [are] the weather conditions kind of looking like?”

Schwing: Using AI to forecast sea ice extent isn’t a novel approach, but it is gaining traction. A team led by the British Antarctic Survey’s Tom Anderson published a study two years ago in the journal Nature Communications. In a YouTube video that year, Tom touted the benefits of his team’s model, called IceNet.

[CLIP: Anderson speaks in YouTube video: “What we found is super surprising. IceNet actually outperformed one of the leading physics-based models in these long-range sea ice forecasts of two months and beyond while also running thousands of times faster. So IceNet could run on a laptop while previous physics-based methods would have to run for hours on a supercomputer to produce the same forecasts.”] 

Schwing: One of the biggest limitations when it comes to AI-generated sea ice forecasts is what Leslie calls “the black box.”

Canavera: And you have all of this data. You put it into the artificial intelligence black box, and then you get the answer. And the answer is right. And scientists get very frustrated because they’re like, “Well, tell me what the black box did,” right? And you’re like, “Well, it gave you the right answer.” And so there's a big trend in artificial intelligence that is called XAI, and explainable AI si hwat that kind of relates to and “Why did your artificial intelligence give you the right answer?”

Sometimes, she says, AI happens upon the right answer but for the wrong reasons. That’s why Marika at the National Center for Atmospheric Research says the most effective sea ice forecasts are likely to come from combining both machine learning and five decades’ worth of physics and statistical modeling.

Holland: If machine learning can help to improve those physics-based models, that’s wonderful. And that is kind of the avenues that we’re exploring—is how to use machine learning to improve these physics-based models that then allow us to kind of predict how the climate and the sea ice system are going to change on decadal, multidecadal [kinds] of timescales. 

Schwing: And there’s one piece of the sea ice forecasting puzzle Leslie, who is Alaska Native, believes is irreplaceable: traditional Indigenous knowledge.

Canavera: What's great about traditional Indigenous knowledge and artificial intelligence is that a lot of traditional Indigenous knowledge is data, and artificial intelligence builds models on data. And that’s why it works better than these like dynamical models in being able to incorporate the traditional Indigenous knowledge.

Islamist militants in Mali began a blockade of Timbuktu by cutting road access in August and then shut off river and air routes in an offensive that has put the city once again on the frontline of a jihadist insurgency.

The source for the flood was not heavy rainfall – it was a small glacial lake located in a side valley next to the Mendenhall Glacier.

Glacier-dammed lakes like this are abundant in Alaska. They form when a side valley loses its ice faster than the main valley, leaving an ice-free basin that can fill with water. These lakes may remain stable for years, but often they reach a tipping point, when high water pressure opens a channel underneath the glacier.

The rapid and catastrophic drainage of lake water that follows is called a glacial lake outburst flood, or GLOF for short. The flood waters race downstream over hours or days and often hit unexpectedly.

Glacial lake outburst floods have destroyed homes, infrastructure and human life around the world. They have killed hundreds of people in Europe and thousands of people in both South America and central Asia. Globally, an estimated 15 million people live downstream from these lakes, with those in Asia’s high mountains at greatest risk.

Flooding from a glacial lake in the Himalayas on Oct. 5, 2023, left dozens of people dead in India as water swept away bridges, damaged a hydropower station and flooded small towns. Satellite images showed that the lake level dropped markedly within hours.

I study Alaska’s glacial lakes and the hazards that glacier-dammed lakes in particular can create. Our latest research shows how these lakes are changing as global temperatures rise.

When glaciers hold back lakes

Some glacial lakes are dammed by moraines – mounds of rock and debris that are left behind as a glacier retreats. Too much pressure from extreme rainfall or an avalanche or landslide into the lake can burst these dams, triggering a devastating flood. Officials say that’s likely what happened when the Himalayas’ Lhonak Lake flooded towns in India in October 2023.

Glacier-dammed lakes, like Suicide Basin off of Mendenhall Glacier, are instead dammed by the glacier itself.

These glacial lakes tend to repeatedly fill and drain due to a cyclic opening and closing of a drainage path under the ice. The fill-and-drain cycles can create hazards every couple of years or multiple times a year.

How glacier lake hazards are changing in Alaska

In a new study, we identified 120 glacier-dammed lakes in Alaska, 106 of which have drained at least once since 1985.

These lakes have collectively drained 1,150 times over 35 years. That is an average of 33 events every year where a lake drains its contents, sending a pulse of water downstream and creating potentially hazardous conditions.

Many of these lakes are in remote locations and often go undetected, while others are much closer to communities, such as Suicide Basin, which is within 5 miles of the state capital and has frequently drained over the past decade.

Our study found that, as a whole, glacier-dammed lakes in Alaska have decreased in volume since 1985, while the frequency of outbursts remains unchanged. This suggests a regional decline in the potential hazards from glacier-dammed lakes because less stored water is available, a trend that has been documented for glacier-dammed lakes worldwide.

To better understand this trend, imagine a bathtub. The higher the sides of the tub, the more water it can hold. For a glacier-dammed lake, the glacier acts as a side of the bathtub. Warming air temperatures are causing glaciers to melt and thin, lowering the tub walls and therefore accommodating less water. That reduces the total volume of water available for a potential glacial lake outburst flood.

Smaller lakes, however, have had less significant change in area over time. As the August 2023 event clearly illustrated, even small lakes can have significant effects downstream.

Alaskans witnessed a new record of destruction in Juneau from the flood. The water reached nearly 15 feet at the Mendenhall River gauge – 3 feet above its previous record.

In summer 2023 alone, Alaskans saw record or near-record flooding from multiple glacier-dammed lakes near populated areas or infrastructure, such as Suicide Basin, near Juneau; Skilak Glacier-Dammed Lake, which affects the Kenai River; and Snow Lake, which impacts the Snow River. These lakes have remained about the same volume but have produced some larger floods in recent years.

One possible explanation is that with a thinner and weaker ice dam, the water can drain much more quickly, though further research is needed to understand the mechanics. Regardless, it’s a reminder that these lakes and events are unpredictable.

How will rising temperatures affect these lakes?

Glacier loss in Alaska is accelerating as temperatures rise. Due to the large volume of glaciers and the many intersecting valleys filled with ice in Alaska, there is a high probability that new lakes will develop as side valleys deglaciate, introducing new potential hazards.

Many of these lakes are likely to develop in remote locations, and their presence may only be noticed in satellite images that reveal changes over time.

Given the abundance of glacial lakes and their potential threat to human lives, early warning and monitoring systems are worryingly sparse. Efforts are underway, such as those in the Himalayas and Chile, but further research is needed to develop reliable, low-cost monitoring systems and to improve our understanding of these evolving hazards.