Science

How a water scientist hopes to save California habitats that could be pumped dry

Published

8 months ago

May 26, 2024

How a water scientist hopes to save California habitats that could be pumped dry

WELDON, Calif. —

California is recognized as one of the world’s hotspots of biodiversity, with more species of plants and animals than any other state. And a significant number of the state’s species, from frogs to birds, live in habitats that depend on groundwater.

These rich ecosystems — including spring-fed streams, wetlands, riparian forests and oak woodlands — are vulnerable to declines in groundwater levels. In areas where unchecked pumping from wells severely depletes aquifers, once-thriving wetlands and forests can dry up and die.

Spotting threats to vulnerable natural areas has become a mission for Melissa Rohde, a hydrologist who has spent years analyzing satellite data and water levels in wells to come up with strategies for preventing ecosystems from being left high and dry.

“Nature has been getting the short end of the stick. It basically gets whatever is left behind, which oftentimes is not enough,” Rohde said. “How do we ensure that these ecosystems are protected?”

More than 300 species of birds have been seen at Kern River Preserve.

(Robert Gauthier / Los Angeles Times)

California is the only state with a groundwater law that includes provisions intended to protect groundwater-dependent ecosystems. But the law, adopted in 2014, gives considerable leeway to local agencies in developing water management plans that prevent “significant and unreasonable adverse impacts.”

When Rohde and other scientists examined the local plans for parts of the state that fall under regulation, they found only about 9% of groundwater-dependent ecosystems are adequately protected, while the remaining 91% are vulnerable.

When they looked at the entire state, they determined only 1% of the ecosystems are sufficiently protected under measures adopted to date.

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Rohde has been focusing on finding ways to change that, in California and around the world.

Often working at home, she has pored over satellite data to spot decreases in vegetation greenness during drought, a telltale sign of die-off caused by declining aquifer levels. And she has analyzed how different types of trees, including willows, cottonwoods and oaks, fare when water levels fall depending on the depth of their roots.

Rohde and other researchers recently published a study outlining how California can set targets for maintaining groundwater levels — based on a formula including the type of vegetation, local water data and satellite imagery — to ensure the plants that anchor each ecosystem will be able to reach water and survive during dry times.

Cattle graze at the Kern River Preserve.

“If we don’t have groundwater levels that are able to support these diverse native vegetation ecosystems, then basically we run the risk of losing that important habitat for a lot of our threatened and endangered species,” Rohde said. “When you play around with keeping groundwater levels too deep to support the habitat, then you could lose species, and then that’s irreversible. The consequences can be severe.”

In California’s Mediterranean climate, trees, shrubs and the species they support are naturally adapted to drought. But excessive pumping from wells can push habitats beyond ecological limits by depleting the sources that sustain them.

With humanity’s heating of the planet intensifying droughts, the strains affecting these ecosystems continue to grow.

Already, California has lost the vast majority of its original wetlands to development, water diversions and agriculture. To avoid losing what remains, Rohde said, the state needs “a precautionary and preventative approach that can ensure that these ecosystems can withstand the intensification of droughts in climate change.”

During a recent visit to Kern County, Rohde and several conservation specialists walked in the shade through a lush forest of cottonwood trees near the south fork of the Kern River, visiting a nature preserve she had previously seen only in satellite images.

Scientist Melissa Rohde stands in a riparian forest.

At the edge of a clearing, she came upon the bare, sunbleached skeletons of dead trees.

She said satellite data had revealed that parts of the forest died along this part of the Kern River during the drought between 2012 and 2016.

“That’s because the groundwater levels rapidly declined,” Rohde said.

After that die-off, she said, groundwater levels rebounded in the area, and the native vegetation has been growing back.

A sign reads "Kern River Preserve" on a gate, with trees in the background.

It helps that this forest is protected as part of the Kern River Preserve, which is managed by the National Audubon Society, and that some nearby farmlands have been retired and converted to conservation lands over the years.

The preserve’s managers, working with the organization Ducks Unlimited, have also restored an expanded wetland by diverting water from the river and flooding a section of pastureland where cattle used to graze.

The wetland attracts birds, such as coots and tricolored blackbirds, and also recharges the aquifer that the roots of cottonwoods and willows tap into.

Scientists and conservation specialists stand on a rock formation overlooking a wetland.

The 3,300-acre preserve has expanded as adjacent alfalfa fields have been purchased and agricultural wells have been shut down, said Reed Tollefson, the preserve’s manager. These efforts have helped protect a refuge for birds including willow flycatchers and yellow-billed cuckoos.

As he pointed to several dead trees poking from the living cottonwoods, he said protecting the forest from groundwater pumping and climate change will require additional effort.

“I think it’s tenuous,” he said. “We’ve got more work to do to try and really sustain this.”

The dead trees that have appeared here and elsewhere in California over the past decade represent the sort of die-off that water managers need to focus on preventing, Rohde said.

“It has to be an intentional practice of setting thresholds, monitoring, using satellite data or other scalable means to measure the impacts, in order to make sure that we are not allowing this to happen on a wider scale,” she said. “From a biodiversity perspective, it’s absolutely critical.”

Rohde said she felt hopeful seeing the forest rebounding and much greener than it was several years ago, with many young trees coming up.

Some other parts of California haven’t fared nearly as well.

One rainy day last month, Rohde visited an area along the Santa Clara River in Ventura County where several hundred acres of willows and cottonwoods dried up and died during the drought in the mid-2010s.

When groundwater pumping by farms and communities caused aquifer levels to fall, many trees died along the river near the city of Fillmore.

“We saw this catastrophic drop in groundwater at this site,” Rohde said.

She visited the area with a research colleague and two managers from The Nature Conservancy. They stood on a gravel road next to a lemon grove, checking on what remained of the forest.

Scientist Melissa Rohde stands beside tall reeds.

Where native trees died, an explosion of invasive reeds has taken over. The nonnative reeds, called arundo, have grown into thickets more than 20 feet tall. And unlike willows, Rohde said, arundo offers little value as habitat for birds.

“When we had that massive die-off, and the groundwater levels remained deep, there was no way for the native vegetation to regenerate,” she said. “But arundo is extremely efficient at extracting soil moisture. And so it was able to outcompete the native vegetation.”

She said efforts to prevent this sort of habitat degradation should be prioritized.

When managers of local agencies set goals for maintaining groundwater levels, she said, they can tailor targets to the type of vegetation — whether there are cottonwood trees, with roots averaging about 9 feet long, or oaks, with roots that average nearly 30 feet but can grow much deeper.

Her colleague Michael Bliss Singer said when native trees are ravaged by multiple years of low water levels, they will start losing leaves and then dropping branches.

In one study, Singer and others documented a “brown wave” of trees drying along the Santa Clara River between 2012 and 2016 — a loss they saw in satellite images.

“It’s completely transformed the ecosystem here,” said Singer, a professor at Cardiff University in Wales who is also a researcher at UC Santa Barbara.

When plants die off like this and don’t recover, it’s a symptom of an ecosystem in decline. To prevent more of these losses in an era when climate change is driving more severe droughts, Singer said, it’s crucial to “come up with creative solutions for the worst-case scenario.”

Rohde has found in her research, however, that most local groundwater plans in California haven’t adequately accounted for climate projections.

Previously, Rohde did other types of climate research, including a stint in Antarctica in 2010, where she was part of a drilling team collecting ice cores. From that experience, Rohde said she realized that “I didn’t want to spend my career convincing people that climate change was an issue; I wanted to do something about it.”

She wore a faded cap with an Antarctica map, a memento of that trip. Rohde said her recent work is motivated by concerns about the climate crisis and biodiversity, as well as a conviction that proactive steps to protect ecosystems can make a difference.

“I have two young kids. I really want to make sure that I’m doing the best thing that I can to ensure a sustainable future for them, where they can access nature,” Rohde said.

A man holds binoculars as he observes a wetland.

“Often groundwater is out of sight, out of mind,” she said. “We don’t measure it, we don’t understand it and we misuse it. And we need to make sure that we are managing groundwater so that it is supporting us, and making sure that we have a sustainable future.”

Rohde now works as an independent scientist. Previously, as a researcher for The Nature Conservancy, she helped write an atlas of threatened and endangered species that rely on groundwater.

California’s groundwater-dependent ecosystems lie not only along streams, but also in habitats such as mountain meadows, coastal redwood forests and mesquite bushes among desert sand dunes. The species they support range from tiger salamanders to desert pupfish, and from songbirds to mammals such as ground squirrels and bighorn sheep.

“The risks are high when species are on the verge of extinction,” Rohde said.

Rohde and other scientists have found that ecosystems sustained by groundwater are under threat worldwide. Some of the few regions that have measures intended to protect them, she said, include Australia, the European Union and California.

Still, even with California’s groundwater regulations and endangered species laws, Rohde said, “we continue to miss the mark in actually protecting them.”

Rohde said state officials should give local water agencies clear direction to ensure they’re using science-based methods to safeguard ecosystems in their state-mandated plans. She said agencies can now use the approaches scientists have outlined to map strongholds of biodiversity and set targets for maintaining aquifer levels.

“It’s very attainable,” she said. “Now, it’s just basically up to political will, or enforcement by the Department of Water Resources, to ensure that that happens.”

Walking in the rain at the Santa Clara River Preserve, Rohde followed her former Nature Conservancy colleagues Peter Dixon and E.J. Remson on a trail through a stand of healthy trees.

A man in a hooded rain jacket hikes along a soaked trail.

They stood on the banks of the fast-flowing river, watching the muddy water churn past.

In the summer and fall, this part of the river usually dwindles to a trickle.

And during the next drought, when the river dries up, the forest will depend on the same groundwater that nearby communities and farms also use.

If the water needs of this and other ecosystems aren’t prioritized, Rohde said, vital habitats will suffer.

“We need to be deliberate about the planning, and ensuring that they get their fair share,” she said. “Their existence is potentially imperiled if we don’t act.”

Science

2024 Brought the World to a Dangerous Warming Threshold. Now What?

Published

5 hours ago

January 10, 2025

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2024 Brought the World to a Dangerous Warming Threshold. Now What?

Source: Copernicus/ECMWF

Note: Temperature anomalies relative to 1850-1900 averages.

At the stroke of midnight on Dec. 31, Earth finished up its hottest year in recorded history, scientists said on Friday. The previous hottest year was 2023. And the next one will be upon us before long: By continuing to burn huge amounts of coal, oil and gas, humankind has all but guaranteed it.

The planet’s record-high average temperature last year reflected the weekslong, 104-degree-Fahrenheit spring heat waves that shuttered schools in Bangladesh and India. It reflected the effects of the bathtub-warm ocean waters that supercharged hurricanes in the Gulf of Mexico and cyclones in the Philippines. And it reflected the roasting summer and fall conditions that primed Los Angeles this week for the most destructive wildfires in its history.

“We are facing a very new climate and new challenges, challenges that our society is not prepared for,” said Carlo Buontempo, director of the Copernicus Climate Change Service, the European Union monitoring agency.

But even within this progression of warmer years and ever-intensifying risks to homes, communities and the environment, 2024 stood out in another unwelcome way. According to Copernicus, it was the first year in which global temperatures averaged more than 1.5 degrees Celsius, or 2.7 degrees Fahrenheit, above those the planet experienced at the start of the industrial age.

For the past decade, the world has sought to avoid crossing this dangerous threshold. Nations enshrined the goal in the 2015 Paris agreement to fight climate change. “Keep 1.5 alive” was the mantra at United Nations summits.

Yet here we are. Global temperatures will fluctuate somewhat, as they always do, which is why scientists often look at warming averaged over longer periods, not just a single year.

But even by that standard, staying below 1.5 degrees looks increasingly unattainable, according to researchers who have run the numbers. Globally, despite hundreds of billions of dollars invested in clean-energy technologies, carbon dioxide emissions hit a record in 2024 and show no signs of dropping.

One recent study published in the journal Nature concluded that the absolute best humanity can now hope for is around 1.6 degrees of warming. To achieve it, nations would need to start slashing emissions at a pace that would strain political, social and economic feasibility.

But what if we’d started earlier?

By spewing heat-trapping gases into the atmosphere, humankind has lifted global temperatures to record highs.

If nations had started reducing emissions in 2005, they could have made gradual cuts to limit warming to 1.5 degrees.

Starting in 2015, when the Paris agreement was adopted, would have required steeper cuts.

Starting today would require cuts so drastic as to appear essentially impossible.

“It was guaranteed we’d get to this point where the gap between reality and the trajectory we needed for 1.5 degrees was so big it was ridiculous,” said David Victor, a professor of public policy at the University of California, San Diego.

The question now is what, if anything, should replace 1.5 as a lodestar for nations’ climate aspirations.

“These top-level goals are at best a compass,” Dr. Victor said. “They’re a reminder that if we don’t do more, we’re in for significant climate impacts.”

The 1.5-degree threshold was never the difference between safety and ruin, between hope and despair. It was a number negotiated by governments trying to answer a big question: What’s the highest global temperature increase — and the associated level of dangers, whether heat waves or wildfires or melting glaciers — that our societies should strive to avoid?

The result, as codified in the Paris agreement, was that nations would aspire to hold warming to “well below” 2 degrees Celsius while “pursuing efforts” to limit it to 1.5 degrees.

Even at the time, some experts called the latter goal unrealistic, because it required such deep and rapid emissions cuts. Still, the United States, the European Union and other governments adopted it as a guidepost for climate policy.

Christoph Bertram, an associate research professor at the University of Maryland’s Center for Global Sustainability, said the urgency of the 1.5 target spurred companies of all kinds — automakers, cement manufacturers, electric utilities — to start thinking hard about what it would mean to zero out their emissions by midcentury. “I do think that has led to some serious action,” Dr. Bertram said.

But the high aspiration of the 1.5 target also exposed deep fault lines among nations.

China and India never backed the goal, since it required them to curb their use of coal, gas and oil at a pace they said would hamstring their development. Rich countries that were struggling to cut their own emissions began choking off funding in the developing world for fossil-fuel projects that were economically beneficial. Some low-income countries felt it was deeply unfair to ask them to sacrifice for the climate given that it was wealthy nations — and not them — that had produced most of the greenhouse gases now warming the world.

“The 1.5-degree target has created a lot of tension between rich and poor countries,” said Vijaya Ramachandran, director for energy and development at the Breakthrough Institute, an environmental research organization.

Costa Samaras, an environmental-engineering professor at Carnegie Mellon University, compared the warming goals to health officials’ guidelines on, say, cholesterol. “We don’t set health targets on what’s realistic or what’s possible,” Dr. Samaras said. “We say, ‘This is what’s good for you. This is how you’re going to not get sick.’”

“If we were going to say, ‘Well, 1.5 is likely out of the question, let’s put it to 1.75,’ it gives people a false sense of assurance that 1.5 was not that important,” said Dr. Samaras, who helped shape U.S. climate policy from 2021 to 2024 in the White House Office of Science and Technology Policy. “It’s hugely important.”

Scientists convened by the United Nations have concluded that restricting warming to 1.5 degrees instead of 2 would spare tens of millions of people from being exposed to life-threatening heat waves, water shortages and coastal flooding. It might mean the difference between a world that has coral reefs and Arctic sea ice in the summer, and one that doesn’t.

Each tiny increment of additional warming, whether it’s 1.6 degrees versus 1.5, or 1.7 versus 1.6, increases the risks. “Even if the world overshoots 1.5 degrees, and the chances of this happening are increasing every day, we must keep striving” to bring emissions to zero as soon as possible, said Inger Anderson, the executive director of the United Nations Environment Program.

Officially, the sun has not yet set on the 1.5 target. The Paris agreement remains in force, even as President-elect Donald J. Trump vows to withdraw the United States from it for a second time. At U.N. climate negotiations, talk of 1.5 has become more muted compared with years past. But it has hardly gone away.

“With appropriate measures, 1.5 Celsius is still achievable,” Cedric Schuster, the minister of natural resources and environment for the Pacific island nation of Samoa, said at last year’s summit in Azerbaijan. Countries should “rise to the occasion with new, highly ambitious” policies, he said.

To Dr. Victor of U.C. San Diego, it is strange but all too predictable that governments keep speaking this way about what appears to be an unachievable aim. “No major political leader who wants to be taken seriously on climate wants to stick their neck out and say, ‘1.5 degrees isn’t feasible. Let’s talk about more realistic goals,’” he said.

Still, the world will eventually need to have that discussion, Dr. Victor said. And it’s unclear how it will go.

“It could be constructive, where we start asking, ‘How much warming are we really in for? And how do we deal with that?’” he said. “Or it could look very toxic, with a bunch of political finger pointing.”

Methodology

The second chart shows pathways for reducing carbon emissions that would have a 66 percent chance of limiting global warming this century to 1.5 degrees Celsius above the preindustrial average.

Science

U.S. Efforts to Cut Emissions Stalled in 2024 as Power Demand Surged

Published

13 hours ago

January 9, 2025

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U.S. Efforts to Cut Emissions Stalled in 2024 as Power Demand Surged

America’s efforts to cut its climate change pollution stalled in 2024, with greenhouse gas emissions dropping just a fraction, 0.2 percent, compared to the year before, according to estimates published Thursday by the Rhodium Group, a research firm.

Despite continued rapid growth in solar and wind power, emissions levels stayed relatively flat last year because demand for electricity surged nationwide, which led to a spike in the amount of natural gas burned by power plants.

The fact that emissions didn’t decline much means the United States is even further off-track from hitting President Biden’s goal of slashing greenhouse gases 50 percent below 2005 levels by 2030. Scientists say all major economies would have to cut their emissions deeply this decade to keep global warming at relatively low levels.

Since 2005, United States emissions have fallen roughly 20 percent, a significant drop at a time when the economy has also expanded. But to meet its climate goals, U.S. emissions would need to decline nearly 10 times as fast each year as they’ve fallen over the past decade. That seems increasingly unlikely, experts say, especially since President-elect Donald J. Trump has promised to dismantle Mr. Biden’s climate policies and promote the production of fossil fuels, the burning of which generates greenhouse gases.

“On the one hand, it is notable that we’ve now seen two years in a row where the U.S. economy grew but emissions went down,” said Ben King, an associate director at the Rhodium Group. “But it’s far from enough to achieve our climate targets.”

The biggest reason that U.S. emissions have fallen in recent years is that electric utilities have been retiring their older, dirtier coal-fired power plants and replacing them with cheaper and less-polluting natural gas, wind and solar power. That trend mostly continued last year, with a few unexpected ups and downs.

The nation’s demand for electricity, which has stayed more or less flat for two decades, suddenly jumped by roughly 3 percent in 2024, in large part because scorching heat during the summer caused many Americans to crank up their air-conditioners. A smaller factor was that tech companies have been building more energy-hungry data centers in states like Virginia and Texas.

While power companies installed large numbers of wind turbines, solar panels and batteries last year to meet rising demand, natural gas use also rose to record highs, while coal use declined only slightly. The net result was that emissions from the power sector increased an estimated 0.2 percent, according to the Rhodium Group.

At the same time, transportation, the nation’s largest source of greenhouse gases, saw an 0.8 percent rise in emissions last year. Gasoline and jet fuel consumption both increased as Americans continued to drive and fly more after the pandemic. Nearly 10 percent of new car sales in 2024 were less-polluting electric vehicles, but those models still make up a small fraction of total cars on the road and have yet to put a major dent in transportation emissions.

On the flip side, emissions from America’s industrial sector — which includes steel, cement and chemicals — fell by 1.8 percent in 2024. Some of that may have been the result of lost output, as two hurricanes and a strike at the nation’s ports disrupted some factory activity in the fall, Mr. King said.

“It’s a reminder that there’s always some bumpiness in emissions,” Mr. King said. “It’s not just a question of how many electric vehicles are on the road or how much solar we’ve installed. A big portion of our economy still relies on fossil fuels.”

One of the most striking findings in this year’s data was that emissions from oil and gas operations dropped roughly 3.7 percent in 2024. Even though the United States produced record amounts of oil and near-record amounts of natural gas last year, many companies appear to have curbed leaks of methane, which is the main ingredient in natural gas and which can seep into the atmosphere and contribute significantly to global warming.

Over the past few years, the Biden administration and several states have adopted new regulations that require oil and gas producers to detect and fix methane leaks. Many companies also have financial incentives to capture methane to sell rather than vent it into the air.

Between 2014 and 2024, U.S. companies appear to have reduced the amount of methane that escaped, per each cubic feet of gas they produced, by 40 percent, according to the Rhodium Group.

Several experts have estimated that greenhouse gases generated in the United States could start dropping sharply in the years ahead if many clean energy policies stay in place, particularly the 2022 Inflation Reduction Act that pumped hundreds of billions of dollars into low-carbon energy technologies such as electric vehicles, wind turbines, solar panels, nuclear reactors, green hydrogen and batteries.

While Mr. Trump has pledged to scrap many of Mr. Biden’s subsidies and tax credits for electric vehicles and low-carbon energy, it remains to be seen whether Congress will agree.

That law has not yet had a major impact on the country’s emissions, said Mr. King, since it takes time for new factories to open and power plants to get built. But, he said, data shows that low-carbon energy and transportation now make up fully 5 percent of total U.S. private investment.

“That’s a leading indicator that things are changing quickly,” he said.

Science

How to protect yourself from the smoke caused by L.A. wildfires

Published

1 day ago

January 9, 2025

Press Room

How to protect yourself from the smoke caused by L.A. wildfires

You don’t have to live close to a wildfire to be affected by its smoke. With severe winds fanning the fires in and around Pacific Palisades, the Pasadena foothills and Simi Valley, huge swaths of the Southland are contending with dangerous air quality.

Wildfire smoke can irritate your eyes, nose, throat and lungs. The soot may contain all kinds of dangerous pollutants, including some that may cause cancer. The tiniest particles in smoke can travel deep into your lungs or even enter your bloodstream.

Conditions like these aren’t good for anyone, but they’re particularly bad for people in vulnerable groups, including children, those with asthma or other respiratory conditions, people with heart disease and those who are pregnant.

Here’s what you should know to keep yourself safe.

Stay indoors

Minimize your exposure to unhealthy air by staying inside and keeping your doors and windows shut.

If you have a central heating and air conditioning system, you can keep your indoor air clean by turning it on and keeping it running. Make sure the fresh-air intake is closed so that you’re not drawing in outdoor air.

Keep your pets inside

They shouldn’t breathe the unhealthy air either.

Check your air filters

Clean filters work better than dirty ones, and high-efficiency filters work better than regular ones. The California Air Resources Board and the South Coast Air Quality Management District recommend filters with a MERV rating of 13 or higher.

You might consider using portable high-efficiency air cleaner in a room where you spend the most time. The U.S. Environmental Protection Agency has information about them here, and CARB has a list of certified cleaning devices here.

Don’t pollute your indoor air

That means no burning candles or incense. If your power is out and you need to see in the dark, you’re much better off with a flashlight or headlamp.

If you’re cold, bundle up. This is not the time to start a cozy fire in the fireplace. Don’t use a gas stove or wood-fired appliances, since these will make your indoor air quality worse, not better, the AQMD says.

The CDC also advises against vacuuming, since it can stir up dust and release fine particles into the air.

Take care when cleaning up

You don’t want your skin to come into contact with wildfire ash. That means you should wear long sleeves, pants, gloves, socks and shoes. The AQMD even wants you to wear goggles.

If you’re sweeping up ash outdoors, get a hose and mist it with water first. That will keep it from flying up in the air as you move it around. Once the ash is wet, sweep it up gently with a broom or mop. Bag it up in a plastic bag and throw it away.

It’s a good idea to wash your vehicles and outdoor toys if they’re covered in ash. Try not to send ashy water into storm drains. Direct the dirty water into ground areas instead, the AQMD advises.

Those with lung or heart problems should avoid clean-up activities.

Discard spoiled food…

If you lost power for a significant length of time, the food in your refrigerator or freezer may be spoiled.

Food kept in a fridge should stay safe for up to four hours if you’ve kept the door closed. If you’ve been without power for longer than that, you’ll need to toss all perishable items, including meat, poultry, fish, eggs, milk and cut fruits and vegetables. Anything with “an unusual smell, color, or texture” should be thrown out as well, according to the U.S. Centers for Disease and Control Prevention.

Refrigerated medicines should be OK unless the power was out for more than a day. Check the label to make sure.

…even if it was in the freezer

Your freezer may be in better shape, especially if it’s well-stocked. Items in a full freezer may be safe for up to 48 hours if it’s been kept shut, and a half-full freezer may be OK for up to 24 hours. (The frozen items help keep each other cold, so the more the better.)

If items have remained below 40 degrees Fahrenheit (4 degrees Celsius) or you can still see ice crystals in them, they may be OK to use or refreeze, according to the federal government’s food safety website.

Ice cream and frozen yogurt should be thrown out if the power goes out for any amount of time. Meat, poultry, seafood, eggs, milk and most other dairy products need to go if they were exposed to temperatures above 40 degrees F for two hours or longer. The same goes for frozen meals, casseroles, soups, stews and cakes, pies and pastries with custard or cheese fillings.

Fruit and fruit juices that have started to thaw can be refrozen unless they’ve started to get moldy, slimy or smell like yeast. Vegetables and vegetable juices should be discarded if they’ve been above 40 degrees F for six hours or more, even if they look and smell fine.

Breakfast items like waffles and bagels can be refrozen, as can breads, rolls, muffins and other baked goods without custard fillings.

Consider alternative shelter

If you’ve done everything you can but your eyes are still watering, you can’t stop coughing, or you just don’t feel well, seek alternative shelter where the air quality is better.

Hold off on vigorous exercise

Doing anything that would cause you to breathe in more deeply is a bad idea right now.

Mask up outdoors

If you need to be outside for an extended time, be sure to wear a high-quality mask. A surgical mask or cloth mask won’t cut it — health authorities agree that you should reach for an N95 or P-100 respirator with a tight seal.

Are young children at greater risk of wildfire smoke?

Very young children are especially vulnerable to the effects of wildfire smoke because their lungs are still rapidly developing. And because they breathe much faster than adults, they are taking in more toxic particulate matter relative to their tiny bodies, which can trigger inflammation, coughing and wheezing.

Any kind of air pollution can be dangerous to young children, but wildfire smoke is about 10 times as toxic for children compared to air pollution from burning fossil fuels, said Dr. Lisa Patel, clinical associate professor of pediatrics at Stanford Children’s Health. Young children with preexisting respiratory problems like asthma are at even greater risk.

Patel advises parents to keep their young children indoors as much as possible, create a safe room in their home with an air purifier, and try to avoid using gas stoves to avoid polluting the indoor air.

Children over the age of 2 should also wear a well-fitting KN95 mask if they will be outdoors for a long period of time. Infants and toddlers younger than that don’t need to mask up because it can be a suffocation risk, Patel said.

What are the risks for pregnant people?

Pregnant people should also take extra precautions around wildfire smoke, which can cross the placenta and affect a developing fetus. Studies have found that exposure to wildfire smoke during pregnancy can increase the risk of premature birth and low birth weight. Researchers have also linked the toxic chemicals in smoke with maternal health complications including hypertension and preeclampsia.

What about other high-risk populations?

Certain chronic diseases including asthma, chronic obstructive pulmonary disease or other respiratory conditions can also make you particularly vulnerable to wildfire smoke. People with heart disease, diabetes and chronic kidney disease should take extra care to breathe clean air, the CDC says. The tiny particles in wildfire smoke can aggravate existing health problems, and may make heart attacks or strokes more likely, CARB warns.

Get ready for the next emergency

Living in Southern California means another wildfire is coming sooner or later. To prepare for the bad air, you can:

Stock up on disposable respirators, like N95 or P-100s.
Have clean filters ready for your A/C system and change them out when things get smoky.
Know how to check the air quality where you live and work. The AQMD has an interactive map that’s updated hourly. Just type in an address and it will zoom in on the location. You can also sign up to get air quality alerts by email or on your smartphone.
Know where your fire extinguisher is and keep it handy.
If you have a heart or lung condition, keep at least five days’ worth of medication on hand.

Times staff writer Karen Garcia contributed to this report.