Climate Central

Climate Central is a nonprofit science and media organization created to provide clear and objective information about climate change and its potential solutions.
  1. Following a year of weather extremes, disasters and policy clashes, we asked our readers to help us pick out the most important climate stories from the U.S. in 2017. Here's what you said.


    This was a brutal year for hurricanes in the U.S. A trifecta of storms (Harvey, Irma and Maria) battered Florida, the Gulf Coast and Puerto Rico, causing deaths and widespread destruction, driving many from their homes. Climate change is fueling hurricanes by increasing their rainfall, wind speeds, and storm surges. Our World Weather Attribution team was among the groups of scientists that found climate change increased the amount of flooding rainfall from Harvey.


    Sea-level rise projections got worse for U.S. coastal communities. New research factoring in the projected effects of warming on Antarctic ice outlined new scenarios for Gulf Coast and East Coast cities, where more than 10 feet of sea-level rise is possible in places this century. Sea-level rise could be kept to less than two feet if we aggressively curb our greenhouse gas emissions, reducing risks and impacts.


    The Trump administration worked to reverse climate protections this year, seeking to replace the Clean Power Plan and eventually withdraw from the Paris Agreement. The administration has been removing the phrase “climate change” from government websites and it greenlighted construction of the Keystone XL oil pipeline. All the while, hundreds of thousands of people marched for science and the climate, and states and cities and nations abroad vowed to fight harder to slow global warming.


    2017 was the year of Tesla co-founder Elon Musk. From a battery factory in Nevada, to South Australia where his batteries are helping a wind farm provide reliable power, to a new energy grid in hurricane-ravaged Puerto Rico, Tesla has taken the lead in producing batteries for energy storage and to power electric cars. And it has developed new all-electric semi trucks and solar shingles!


    California is battling its largest wildfire on record right now, but this wildfire season wasn’t just bad for the Golden State. Wildfires burned more than 9.5 million acres across the U.S., destroying neighborhoods and releasing dangerous smoke pollution. The Western wildfire season is 105 days longer than it was 45 years ago as climate change fuels more and bigger blazes.


    2017 is likely to be the third-hottest year on record for the U.S., behind 2016 and 2012. This record heat is particularly astounding considering the absence of an El Niño, which usually boosts global temperatures. If the final data matches expectations, five of the 10 hottest years on record will have come since 2006.


    The homes of Americans were destroyed or threatened by extreme weather and rising seas, with the poor hit the hardest. Hundreds of thousands of people had to flee Puerto Rico after Hurricane Maria devastated the island, relocating to Florida and other areas. Thousands more in New Jersey and Louisiana are hoping for federal help as they grapple with the ongoing effects of flooding linked to rising seas and climate change-fueled storms.


    Production of clean energy climbed as prices continued to come down. In March, 10 percent of all electricity generated in the U.S. came from wind and solar, with help from Texas (America’s number 1 wind provider) and California (the largest solar producer). Bloomberg New Energy Finance concluded in the summer that solar energy can now be as cheap as power from new coal plants in the U.S.


    Your car is contributing to the biggest source of U.S. emissions. Transportation recently overtook electricity generation as the biggest source of greenhouse gases from the U.S., as coal power plants were retired and replaced with renewables and natural gas facilities.


    It may be winter right now, but don’t forget about extreme heat, which is the number one weather-related killer. Climate change made a February heat wave across much of the eastern U.S. three times more likely. In June, another heat wave in the Southwest prevented planes in Arizona from taking off. Danger days are surging from Power, Montana to New York City, and a dramatic rise in dangerous heat and humidity will continue in the summertime.

  2. Research Report by Climate Central

    Antarctic ice sheet models double the sea-level rise expected this century if global emissions of heat-trapping pollution remain high, according to a new study led by Dr. Robert Kopp of Rutgers University and co-authored by scientists at Climate Central.

    Global average sea level is expected to rise by one foot between 2000 and 2050 and by several more feet by the end of the century under a high-pollution scenario because of the effects of climate change, according to the projections in the new peer-reviewed study. It shows 21st century sea-level rise could be kept to less than two feet if greenhouse gas emissions are aggressively and immediately reduced, reflecting a larger gap in sea-level consequences between high and low emissions scenarios than previous research has indicated.

    High-pollution projection for Norfolk and Portsmouth, Virginia in 2100. See interactive map here.

    The study provides a median projection for sea-level rise of 146 cm (4’9”) during the 21st century under a high-pollution scenario known as RCP8.5 (see Table 1), when results from new modeling of Antarctic ice sheet behavior are included. The Intergovernmental Panel on Climate Change’s most recent report, published in 2014, which assumed the Antarctic ice sheet would remain stable, provided a median projection for the same scenario during a similar time period of 74 cm (2’5”).

    Previous efforts to project future sea levels have combined projections for future levels of greenhouse gas pollution with findings from research into the effects of that pollution in warming oceans and melting glaciers. Those efforts have either excluded the possibility of ice sheet break-ups on the margins of Greenland and Antarctica, left out the consequential new mechanism of marine ice-cliff instability, or relied on experts’ opinions regarding these potential impacts.

    Ice loss in Antarctica could do more to raise sea levels than all of the other factors combined, and recent ice sheet modeling developed by Robert DeConto of University of Massachusetts and David Pollard of Pennsylvania State University has indicated the continent’s ice reserves may be less stable than previously thought.

    The new study,  “Evolving understanding of Antarctic ice-sheet physics and ambiguity in probabilistic sea-level projections,” combined the results of the modeling by DeConto and Pollard with sea-level rise projections published in 2014 and since employed by multiple cities, states and federal agencies. The new study, led by Kopp, was published Dec. 13 in the journal Earth’s Future. Other scientists involved with the research are affiliated with Columbia University, Harvard University, Princeton University, Boston College and Climate Central.

    The study projects a range of potential levels of sea rise under different greenhouse gas emissions scenarios. Even the lowest levels of projected sea-level rise would require heavy investments in adaptation efforts and could require residents and businesses to relocate. Greater levels of sea-level rise increase economic and social impacts.

    The median projection for sea-level rise from 2000 to 2050 in the study was roughly 30 cm (one foot) under RCP8.5. The research indicated that sea levels in 2050 will be affected little by the amount of greenhouse gas pollution that’s released during the coming years.

    The new projections warn of runaway risks during the second half of the century, with those risks substantially higher if current levels of greenhouse gas emissions continue.

    Under the high-pollution RCP8.5 scenario, the study’s median projection for the period 2000 to 2100 is for 146 cm (4’9”) of global average sea-level rise. According to the research, local rise would vary from region to region under the same scenario, and would exceed the global average for all U.S. Gulf and Atlantic coast locations, ranging up to 225 cm (7’5”) or more in Louisiana.

    Two of the authors of the paper were Climate Central’s Benjamin Strauss and Scott Kulp. For the study, the pair mapped local sea level rise projections worldwide, and calculated that, unless new protections are built, water could permanently inundate land currently home to 153 million people (see Table 2). For perspective, that is nearly half of the U.S. population, and more than three times the estimated number of refugeesworldwide at the end of 2016. This assessment used available global elevation data from NASA.  As these elevation data are known to significantly underestimate coastal exposure to sea-level rise, the affected population could be substantially larger.

    90 percent of the study’s simulations found that global sea-level rise will be between 93 cm (3’1”) and 243 cm (8’) during the 21st century under RCP8.5. Under the high-end 8-foot scenario, impacts would be particularly heavy in the continental U.S., where sea level would rise substantially more than the global average. Due to regional effects driven mainly by land subsidence and gravitational effects linked to ice mass loss from Antarctica, sea-level rise of 9 to 11 feet would be expected along densely populated Gulf and Atlantic coasts.

    Under an alternative scenario, known as RCP2.6, in which emissions are aggressively and immediately reduced, the study projects a median sea-level rise of 56 cm (1’10”) during the 21st century.

    The research cannot yet assign likelihoods to different sea-level outcomes, but it explores a wide range of possibilities, making the median (central) values relatively robust. The study represents an important early step at integrating Antarctic physics into sea-level projections.

    For a further perspective, read Kopp's blog at the Climate Impact Lab.

  3. By John Upton (Climate Central) and Kate Wheeling (Pacific Standard)

    David Ewing wore a bright white dust mask, his face behind it puffy and red, as he sat on a stone bench in downtown Santa Barbara, California. A fine layer of ash covered the pavement at his feet, dirty residue from wildfires ravaging the region.

    “When I woke up yesterday I couldn't breathe,” said Ewing, who is homeless and has been diagnosed with cancer. He spent the previous night sleeping behind a Saks department store. “This stuff is just wiping me out.”

    Smoke from the Thomas Fire, viewed from Santa Barbara on December 5, 2017.
    Credit: Doc Searls/Flickr

    Ewing is among the tens of thousands of homeless in Southern California who are struggling to escape the smoke as wildfires tear through the region. Experts caution against spending time outdoors when it’s smoky, but for many, staying inside isn't an option.

    This story was produced through a partnership with Pacific Standard. It's part of a Climate Central series on wildfire pollution, climate change and public health supported by the Bill Lane Center for the American West at Stanford University. Climate Central also published a research report on this topic.

    Wildfire seasons have been growing longer and more severe throughout the American West. Heat-trapping pollution and the effects of weather cycles have pushed up temperatures. Meanwhile, saplings and other fuel for fires has accumulated in forests. That’s stoking blazes that are undermining long-running efforts to clean the air using environmental regulations.

    “When we have warm conditions, that tends to draw more moisture out of vegetation,” said John Abatzoglou, a geographer at the University of Idaho who studies climate change and wildfires. “It tends to accelerate the rate at which vegetation dries up and becomes receptive to igniting and carrying fire.”

    Wildfire smoke can travel hundreds of miles and blanket valleys and regions, creating what scientists call smoke waves. Smoke waves are pulses of bad air caused by fires that linger stubbornly for days, similar to heat waves.

    Smoke contains chemicals from burning rubber and homes. It can also worsen ozone pollution. And it’s filled with tiny particles known as PM2.5, which can lodge inside lungs, trigger coughing, worsen diseases like asthma, and lead to long-term damage including cancer.

    Climate change-focused research published in the journal Environmental Research Letters a year ago concluded smoke could send 30 more people to hospitals across the West each year during the late 2040s than was the case 40 years earlier as smoke waves become more frequent and severe, mostly in the late summer and early fall. Some counties were projected to see little or no change. Impacts could be heavy in parts of central Colorado and Washington — and in Southern California.

    “The larger the fire, the more people are affected, and the worse the health impacts will be,” said Loretta Mickley, a Harvard University researcher who worked on the study. “It’s just one more consequence of our love of emitting these greenhouse gases. So it’s one more reason to think about, ‘OK, let’s cut these emissions back.’”

    Even a state with some of America’s most rigorous and progressive pollution standards can do little to protect itself. “Our state laws and policies and local efforts are all working to drive down smog and soot pollution,” said William Barrett, a policy analyst in California at the non-profit American Lung Association, which has been providing masks to the Red Cross to give to the needy. “But now with our changing environment, we’re seeing longer and more severe fire seasons and, along with that, greater impacts to air quality.”

    As with most pollution, the poorest and frailest are the most vulnerable to smoke waves. A U.S. EPA study of emergency room visits linked to a North Carolina wildfire that burned in 2008 showed health risks from PM2.5 increased in the counties with the poorest residents and with the greatest levels of income inequality.

    In California, where a fast-growing population is fueling a housing crisis, officials and non-profits have been working to protect the homeless population, such as by providing masks. Non-profit workers have also been providing masks to farm workers. Homeless people and farm workers can be especially vulnerable because they often have limited access to health care and have trouble sheltering inside when the smoke outside is heavy.

    Wildfires tore through Southern California this week fueled by hot and dry seasonal winds — called Santa Ana winds — blowing over landscapes left parched by an unusual absence of fall storms. The largest blaze, the Thomas Fire, which raced across the hills of Ventura, was stopped only by the Pacific Ocean after the flames hopped the 101 freeway. At least three others scorched the hills above Los Angeles.

    Photos of the explosive Thomas Fire shown here on December 5, 2017 taken from the cockpit of NASA’s high-flying ER-2 aircraft.
    Credit: Donald “Stu” Broce, provided courtesy of Armstrong Flight Research Center

    “This is probably one of the worst times I've had to deal with it,” said Kevin Ellis, 49, a marijuana farm worker who was walking his gray pit bull next to eerily empty volleyball courts on Santa Barbara’s East Beach on Friday. “It bothers me, I've been working in it — I worked 13 hours yesterday — but I've got a mask.”

    While California’s wildfire trends have in the past been linked to global warming, the fires ravaging Southern California this week have been driven largely by the whims of the weather. “Global warming is there and it’s having an influence,” said Park Williams, a climate and ecology researcher at Columbia University’s Lamont-Doherty Earth Observatory. “But there’s a bunch of other stuff going on too.”

    Homes and palm trees burn in the Creek Fire outside of Los Angeles, California on December 5, 2017.
    Credit: Los Angeles Fire Department/Flickr

    The conditions stoking the blazes in Southern California are projected to become more common and severe in the years ahead as greenhouse gas pollution from fossil fuel burning, deforestation, farming and other industrial practices accumulates in the atmosphere, changing temperatures and rainfall patterns.

    As a thick yellow haze filled the air this week, air quality alerts went out warning residents outside of evacuation zones to seek shelter. Winds late in the week were pushing the smoke far up the California coast, over the Silicon Valley and into San Francisco, affecting millions.

    “It’s been very difficult for outpatients to breathe,” said Laren Tan, a pulmonologist at Loma Linda University in San Bernardino County. He tells patients to stay inside as much as possible when smoke waves hit, and to close their windows and use air filters.

    But even getting indoors can be a major challenge for the homeless in L.A., one of the only U.S. cities where homelessness is rising. In 2017, the number of homeless people climbed to over 55,000 — up more than 13,000 from the year prior. L.A. also has the largest unsheltered subpopulation of any big city, according to Colleen Murphy, an outreach coordinator for the L.A. Homeless Services Authority.

    "In most big cities, there's at least shelters to go to at night. In Los Angeles, 75 percent of our homeless are unsheltered, so that means on any given night, they're sleeping outdoors or in their cars," she said. For comparison, 5 percent of New York City's 76,000 homeless are unsheltered. "It's very challenging even on a good day."

    Since the fires began, outreach teams, which sometimes include medical and mental health professionals, have fanned out across the city to try to get people off the streets and into the city's shelters or a Red Cross facility.

    The southern California wildfires could be seen by the International Space Station crew from their vantage point in low Earth orbit.
    Credit: NASA/flickr

    "We've mobilized our street teams, because we do get that extra bump of beds available during the winter months,” Murphy said. “We're trying to let people know, 'Hey the winter shelters are open, so please let us take you there.'”

    In Ventura County, where as of Friday the Thomas Fire had burned 132,000 acres and more than 400 buildings, workers at the transitional living facility operated by county officials were handing out masks. Some of the homeless are turning up at evacuation shelters as well.

    The fires have struck Southern California at an unusual time and with rare ferocity, bookending a deadly wildfire season that destroyed neighborhoods and killed dozens in wine country north of San Francisco and filled the sweeping Central Valley farming region with smoke from forest fires in mountains nearby.

    The blazes are part of a years-long fiery crisis for the West — one that’s only expected to get worse.

    “How much longer are we going to go through this?,” Ewing said, as he sat on the stone bench, his backpack and a large black garbage bag at his feet. “I'm homeless and I have to breathe it all day long.”


  4. As climate change fuels large wildfires, the pollution they're releasing is making Americans sick and undermining decades of progress in cleaning the air.

    SANTA ROSA, Calif. — As the deadliest fires in California history swept through leafy neighborhoods here, Kathleen Sarmento fled her home in the dark, drove to an evacuation center and began setting up a medical triage unit. Patients with burns and other severe injuries were dispatched to hospitals. She set about treating many people whose symptoms resulted from exposure to polluted air and heavy smoke.

    This story was produced through a partnership between Climate Central and Kaiser Health News with support from the Bill Lane Center for the American West at Stanford University. Kaiser Health News/California Healthline senior correspondent Barbara Feder Ostrov contributed reporting from Santa Rosa.

    “People were coming in with headaches. I had one. My eyes were burning,” said Sarmento, the director of nursing at Santa Rosa Community Health, which provides health care for those who cannot afford it. But respiratory problems — coughs and shortness of breath — were among the biggest risks. “We made sure everyone had a mask.”

    More than half of the evacuees at the shelter that October night were elderly, some from nursing homes who needed oxygen 24/7. Sarmento scrambled to find regulators for oxygen tanks that were otherwise useless. It was a chaotic night — but what came to worry her most were the weeks and months ahead.

    “It looked like it was snowing for days,” Sarmento said of the falling ash. “People really need to take the smoke seriously. You’ve got cars exploding, tires burning. There has to be some long-term effect” on people’s health.

    From Puget Sound to Disneyland and east over the Rockies, Americans have coughed and wheezed, rushed to emergency rooms and shut themselves indoors this year as pollution from wildfires darkened skies and rained soot across the landscape. Even to healthy people, it can make breathing a miserable, chest-heaving experience. To the elderly, the young and the frail, the pollution can be disabling or deadly.

    Even though the nation has greatly improved air quality over the last 40 years through environmental regulations and technological improvements, the increasing frequency of large wildfires now undermines that progress, releasing copious pollutants that spread far and wide through the air and linger long after the fires are extinguished.

    Views of San Francisco's skyline are smoke-filled on the morning of Oct. 9 as multiple wildfires burn in Mendocino and Sonoma counties.
    Credit: Amy Graff/SF Gate

    Scientists say climate change, degraded ecosystems and the fickleness of the weather have been amplifying fires in forests, grasslands and neighborhoods throughout the West. Nine times more western forestland is burning in large fires each year on average now than 30 years ago, according to calculations by two leading scientists.

    The blazes create smoke waves — pulses of pollution containing everything from charred plastic residue to soot to other small particles that lodge deep in the lungs. They can trigger short-term ailments, such as coughing; worsen chronic diseases, such as asthma; and lead to long-term damage, including cancer.

    The effect of the fires in Northern California’s wine country, which destroyed thousands of homes and killed 43 people, went well beyond the burn zone. The smoke choked the San Francisco Bay Area, home to 7 million people in nine counties, for days.

    Colette Hatch, 75, of Santa Rosa, who suffers from lung disease and uses a nebulizer daily, evacuated to her daughter’s home in Sunnyvale, in Silicon Valley, when the fires came. But even nearly 100 miles away, Hatch said she struggled to breathe, coughing so hard she couldn’t sleep.

    Wafting beyond Oakland and Livermore in the East Bay, the smoke headed into California’s agricultural heartland, the Sacramento and San Joaquin valleys.

    Known collectively as the Central Valley, it stretches for hundreds of miles roughly north to south, bracketed by mountain ranges that trap some of the dirtiest air in America. Increasingly, wildfires like the ones in Northern California’s wine country funnel smoke into the chute, significantly raising the pollution levels in places as far away as Fresno.

    Climate Central, a research and journalism nonprofit, examined air district data from California’s Sacramento and San Joaquin valleys. The analysis showed that while the number of heavily polluted days is falling overall each year on average — those days are occurring more frequently during the peak fire season. The researchers say wildfire smoke is to blame.

    Read the full Climate Central report here.

    Monitors in the San Joaquin Valley and San Francisco Bay Area showed levels spiked in October as the wine country fires sullied skies.

    With large wildfires on the rise, smoke and the attendant breathing ailments seemed everywhere this year. In September, smoke from fires burning in California, the Pacific Northwest and Montana pushed as far east as Pennsylvania. Smoke triggered emergency declarations in Washington state and California. The Evergreen State was experiencing few fires of its own in July when it was hit by smoke waves that poured across the Canadian border. And smoke returned to much of the northwest in August and September as fires broke out in the Cascades and the Columbia Gorge.

    “I remember waking up one morning and the sky was orangey-red and there was ash falling out of the sky,” said Jeremy Hess, a researcher and physician at the University of Washington in Seattle. “This summer was very busy for us in the emergency department and we were often over capacity. If it wasn’t the smoke, it was the heat,” Hess said.

    As World Warms, Environment And Health Suffer

    The blazes came after record-breaking late summer heat dried out grass that had flourished following record-breaking winter rains — both forms of extreme weather that are worsened by global warming. In addition, a high pressure system over the Pacific fanned the flames by driving unusually hot and powerful seasonal winds into Northern California from the dry highlands of Nevada.

    The immediate precipitant may have been sparks from power lines, although investigations into the causes are ongoing. But a changing climate helped fuel the blazes.

    “Climate change was not the cause but it’s definitely an ingredient,” said Park Williams, a climate and ecology researcher at Columbia University’s Lamont-Doherty Earth Observatory. And that means worse is to come.

    Williams said there was a clear connection between the nearly 2 degrees Fahrenheit overall increase in global temperature since the late 1800s and the severity of these and other fires. (Warming in the West has been outpacing the global average in recent decades because of natural cycles.)

    “Fire really responds strongly to even that small of a change of temperature,” said Williams, whose assessment of global warming’s role in the wine country fires is shared by other experts.

    Read the full Climate Central report here.

    Environmentally, the fires are a double whammy: They destroy trees that help to slow global warming by absorbing heat-trapping carbon dioxide as they grow. They also release carbon dioxide stored within, as well as black carbon that melts snow and ice.

    Research indicated in 2015 that large fires had helped turn California’s forests and other lands into polluters, releasing more carbon to the atmosphere than they suck back in. The state’s wildlands released more heat-trapping pollution from 2001 through 2010 than Vermont’s entire economy. Rising temperatures aren’t the only cause — the forests are overloaded with fuel following more than a century of aggressive firefighting.

    While public attention has tended to focus on other health risks from climate change such as heat stroke in summer and the spread of mosquito-borne diseases northward, the effects of smoke pollution have been gaining more attention following dramatic and widespread wildfires.

    The most dangerous pollution from wildfires is fine soot — “really small particles that we know can get into the lungs,” said Colleen Reid, a geographer at the University of Colorado who researches climate change and human health. It’s known as PM2.5, meaning “particulate matter” that’s less than 2.5 microns wide, only visible using microscopes.

    It can nestle into lung tissue and pass into the bloodstream, contributing to an array of health problems including infections and, potentially, heart attacks.

    Ed Corn sifts through the ashes of his former home in Santa Rosa’s Coffey Park neighborhood. “I can definitely taste the toxins in my throat and the back of my tongue,” he said.
    Credit: Heidi de Marco/Kaiser Health News

    Symptoms related to smoke waves may not be diagnosed right away, making it hard to recognize the role a fire may have played in an illness or death. Reid led an analysis published a year ago based on hundreds of studies into fire pollution’s health effects. The clearest links shown in the studies were between PM2.5 and asthma and other breathing problems; links to heart disease were less conclusive.

    Researchers from leading American universities examined fire pollution across the West, finding that two of every three counties in the region suffered at least one smoke wave from 2004 through 2009. When they correlated those findings with medical data, they found a 7 percent jump in breathing-related hospitalizations after smoke levels were most extreme.

    “An acute fire lasting, for example, days to weeks, may not show up as an immediate problem but as health problems that may occur over a time span of weeks or months,” said Loretta Mickley, a Harvard researcher who worked on the study.

    This Summer In California

    Elva Hernandez, 51, has lived in the San Joaquin Valley most of her life. She’s suffered from asthma since she was 10. This summer she was stuck inside her house for several weeks as smoke waves suffocated her neighborhood in the small town of Kerman, Calif., near Fresno.

    “The smell, all the dust, the smoke, the smog, everything, it’s just — you can’t breathe,” said Hernandez, a stay-at-home mom whose husband analyzes lab samples at a hospital. “You can’t live your life normally.”

    The San Joaquin Valley is home to 4 million people, many of them poor. One in six children suffers from asthma. Poor people often are most affected by air pollution, partly because they tend to live in more drafty housing in more polluted neighborhoods.

    But enforcement of federal regulations dating to the Nixon administration has been reducing air pollution from fossil fuels and fertilizers in the valley, requiring cleaner engines for trucks and the replacement of outdated equipment on farms.

    “We’ve been seeing a lot of positive trends,” said Jon Klassen, manager of the air monitoring team at the San Joaquin Valley Air Pollution Control District. At the same time, “there’s a lot more emissions coming from these fires. They’re uncontrollable. They’re very difficult to deal with.”

    Read the full Climate Central report here.

    Research looking at air pollution levels helps explain why people like Hernandez are suffering more during fire seasons. The Climate Central analysis of San Joaquin Valley air data showed that while the number of days each year on which levels of PM2.5 exceeded federal standards declined by about 45 percent overall from 2000 to 2016, they increased by almost a third during the peak summer fire season.

    In the Sacramento Valley to the north, summer fire season pollution has been responsible for about 40 percent of the days when federal standards for PM2.5 pollution were exceeded in recent years. That’s up from less than a tenth of them earlier this century, the researchers found.

    Wildfires also release toxic material and chemicals that react in the atmosphere to form ozone pollution, which can hang over neighborhoods as haze. Ozone irritates lungs and throats, triggers shortness of breath and aggravates diseases like bronchitis, emphysema, and asthma.

    Read the full Climate Central report here.

    Hernandez’s asthma doctor, Praveen Buddiga, who operates his own practice in nearby Fresno, treated patients with oxygen and medicine during September fires in the Sierra Nevada mountains, which straddle California and Nevada. He did so again following the wine country fires in October. For asthmatics, the onslaughts of fire pollution are “like pouring a little salt into the wounds,” he said.

    Buddiga suggests his patients limit their time outside, drive with windows rolled up and wear masks when smoke waves hit. Better yet, he advises them to leave the area if possible until the smoke clears.

    But risks can be difficult to gauge for patients and experts who want to offer precautions. Scientists who sampled pollution from wildfires using a NASA jet reported in June that fire pollution is being “significantly underestimated” by the federal government. While fleets of mobile air monitors are deployed near fires to help government agencies project the movement of smoke waves, the network of permanent monitors is sparse.

    “We have no real good way of communicating to people, ‘Hey, the wildfire smoke is really bad in these spots, and this is where you take precautions,’” said Rob Carlmark, a weathercaster with ABC10 in Sacramento whose audience stretches from Bay Area cities to Lake Tahoe at the Nevada border.

    Absent local smoke pollution data, he tells viewers, “The best smoke detector is your nose.”

    Lighting Up To Protect Lungs — and the Planet

    Josh Bien wore a heavy pack and held a hoe in one hand. Using the other, the firefighter dripped a burning mixture of diesel fuel and gasoline on the forest floor from a spouted canister. Saplings and beds of pine needles sizzled and burned around him in a national forest in the Sierra Nevada, an hour’s drive east of Fresno.

    Like smoke from suburban fires in the San Francisco Bay Area, that from large wildfires in the forest of this 600-mile mountain range can travel into the Central Valley. A spate of large fires in August and September created heavy smoke that suffocated foothills towns and drove people like Elva Hernandez indoors.

    Firefighter Josh Biel igniting the forest floor during a prescribed burn in the Sierra National Forest
    Credit: John Upton/Climate Central

    Devastating forest fire seasons in recent years have prompted research pointing to the need for more prescribed burns like this one. They’re set and managed by firefighters and foresters and guided by computer models that predict the spread of fires and their smoke. They’re aimed at removing highly flammable undergrowth and spare the mature trees.

    “You can either do it on your terms,” said Adam Hernandez, a prescribed fire and fuels management officer with the U.S. Forest Service, as gray smoke billowed around, “or you wait for that wildfire to come and it does it on its terms — and then you’re in a bad way.”

    Small fires used to burn regularly through the understories of the Sierra Nevada’s forests, started by lightning and native tribes. That changed after the Native Americans were forced from the mountain range, followed by more than a century of logging and aggressive firefighting.  Those activities replaced stands of large, fire-resistant trees with thickets of smaller ones, building up fuel for enormous blazes.

    “When you have some of these extreme wildfires, you’re creating more harmful emissions,” said Jonathan Long, an ecologist with the U.S. Forest Service. Extreme fires burn larger areas and their flames jump from forest floors to incinerate canopies, producing heavy black smoke and killing mature trees. “We think taking the medicine in small doses is a lot healthier.”

    The excessive undergrowth amplified the impact of California’s recent drought — there was too little water for so many trees. More than 100 million trees may have died across the Sierra Nevada in recent years. The dead trees can provide nesting cavities and their logs create important habitat for wildlife, but some scientists fear they may also intensify fires after they topple into desiccated piles.

    Trees killed by the effects of drought in the Sierra National Forest
    Credit: John Upton/Climate Central

    The federal government has been striking agreements with state agencies to use more prescribed burns and take other steps to better manage forests. In January, California released an ambitious draft plan to restore forests over the decades to come — through a focus on prescribed burns — with the goal of reducing pollution from wildfires.

    “We’re trying to ensure that we have healthy, resilient forests that are net sinks of carbon so that they’re storing more carbon than they’re releasing,” said Russ Henly, a California Natural Resources Agency official who helped draft the plan. By 2020, the plan seeks to double the amount of land treated using prescribed burns to 35,000 acres a year.

    With so many local, state and federal agencies overseeing environmental rules and owning land in California, the state says coordination will be key. For example, the San Joaquin Valley Air Pollution Control District can prevent national parks and other landowners from conducting prescribed burns when pollution levels will be affected — which is most of the time.

    Mindful of the growing danger of big blazes, the air district has become more accommodating of prescribed fires. Still, finding the money to pay for the work remains a challenge.

    Some members of Congress have pushed logging as a way to ease forest fires, though that approach could have the opposite effect: Trees valued by loggers tend to be the largest and most fire-resistant. Troublesome small trees and dead ones have little value other than as fuel for power plants, and even then they’re generally too expensive to gather. Low natural gas prices have been forcing the closure of biomass power plants, which are fueled with wood.

    Even if the money is found to improve forest management, climate change will likely limit the progress from improved forest management, said Christopher Field, an ecology professor at Stanford University. The fire season will continue to lengthen. Landscapes will continue to dry out. “The challenge we still face is how to get out of decades of managing forests in ways that increase, rather than decrease, fire risk,” he said.

    Field oversaw a survey dealing with Sierra Nevada forests completed by 75 academics, government officials and nonprofit and industry employees. While most agreed that prescribed burns and other approaches can lock carbon into the mountain’s ecosystems, they warned it will be difficult to overcome the losses from wildfires as temperatures rise.

    California doesn’t include carbon losses from forest fires when it tallies its progress toward reducing climate pollution. But amid the burning, logging and clearing of forests from Indonesia to the Amazon and the Congo, destructive fires in the forestlands of a U.S. state that has some of the world’s most ambitious climate goals are contributing to the problem.

    And, in the process, they are making people sick.

  5. Research Report by Climate Central
    November 2017


    Read "Breathing Fire," our feature story on fire pollution

    Smoke pollution is leading to serious public health impacts as large wildfires across the American West become more frequent and destructive. These fires are undermining progress made during recent decades in reducing pollution from tailpipes, power plants, and other industrial sources. The increasing frequency and area burned by large fires is linked to human-caused climate change as well as other environmental changes.

    Climate Central analyzed air quality trends from 2000 through 2016 in two large California air basins that are heavily affected by smoke pollution. The analysis focused on particulate matter (PM2.5), a dangerous air pollutant. We found that while the air is getting cleaner overall in recent years, it’s getting dirtier during the fire season —  a season that research has shown is growing longer in the western United States.

    California’s Central Valley — Climate Central Analysis

    The Central Valley is a large, flat region that dominates California’s geographic center. The valley comprises some 11 percent of the state’s land area and includes population centers such as Sacramento and Fresno, but the majority of the region is made up of farmland — some of the most productive on the planet. 

    Central Valley air quality was analyzed because the region is heavily affected by air pollution  that is produced within an even larger geographical area. Bounded by mountain ranges to both the east and the west, the valley’s geographical and meteorological features combine with industrial activity such as truck traffic to contribute to these high levels of pollution. Some of the pollution is generated within the valley, while other pollution sources include wildfires burning along the coast to the west and in the Sierra Nevada mountain range to the east. 

    Wildfires are a source of an especially problematic type of air pollutant known as PM2.5 (“particulate matter” less than 2.5 microns in diameter), which can become lodged in lungs and cause or exacerbate a wide array of health problems such as asthma and heart disease. Emerging evidence suggests PM2.5 could also be linked to premature births. Other PM2.5 sources include a wide variety of industrial and agricultural activities. To protect human health, the U.S. Environmental Protection Agency has established both daily (24-hour) and annual standards for PM2.5 of 35 µg/m3 and 12 µg/m3, respectively.1   

    To examine the contribution of wildfires to levels of PM2.5 in the Central Valley, Climate Central compared the number of days PM2.5 exceeded federal standards at at least one station in each air basin for the entire year, with the number of days the pollutant exceeded federal standards during the summer wildfire season from June to September. The analysis covered the period 2000 to 2016 and was conducted separately for two air basins comprising the Central Valley — the Sacramento Valley and the San Joaquin Valley. Together, these valleys cover 20,000 square miles2 and are home to nearly 6.7 million people.3

    Between 2000 and 2016, air quality in both the Sacramento Valley and the San Joaquin Valley improved, with the number of days per year with 24-hour PM2.5 exceedances falling by roughly 64 percent and 45 percent overall, respectively.  

    Amid this overall trend, a growing percentage of exceedances are occurring during peak fire season and when PM2.5 are typically low. That points to the increasing role of wildfires as a source of air pollution even as emissions from other sources continue to fall. The Sacramento Valley is now seeing some years with 50 to 60 percent of PM2.5 exceedances occurring during these months. In the earlier part of the period studied, summer exceedances typically accounted for less than 10 percent of the total. There has been a 31 percent increase in the number of exceedances during the summer fire season in the San Joaquin Valley compared to the number of exceedances during the summer fire season in 2000. The increase in proportion of summertime exceedances in the Sacramento Valley air basin has been even more dramatic with nearly a five-fold increase.

    Air quality data for the Central Valley prior to 2000 is only partially available. Data prior to 2000 was excluded based on the criterion of having less than 5 percent of the data missing. The data analyzed does not include 2017 because not all winter months have yet occurred this year. Note that winter months historically have the most exceedances.

    Because wildfire smoke can blow across county, state and national borders, the correlation between local PM2.5  and nearby wildfire activity is not exact. Comparing periods of exceedances at local levels with satellite images of smoke, however, provides another line of evidence connecting wildfires to PM2.5 pollution.

    For example, exceedances in PM2.5 concentrations were detected by air quality monitors at three locations in the Central Valley at the beginning of September 2017, with these exceedances coinciding with an outbreak of wildfires. Just a few days later, widespread smoke was still apparent in satellite images of the region, and there is a visible relationship between air quality data and the smoke. Areas where the wildfires are located and smoke is present  largely coincided with measurements showing the worst air quality.

    Major wildfires broke out north of San Francisco in early October, 2017, killing more than 40 people.4 Smoke from these North Bay fires spread throughout the San Francisco Bay Area and reached the Central Valley and beyond. Air in the Bay Area air basin is usually cleaner than in the Central Valley, and it has also experienced an overall decline in the number of days each year that PM2.5 exceeds federal standards. Smoke from the October fires heavily polluted the air, with one day in the Bay Area air basin experiencing twice the level of PM2.5 of any day going back to 2001.

    Climate Change

    Wildfire seasons are projected to become worse due to climate change, expanding in length and increasing the number of large fires and acreage that burns each year.  When compared with the 1970s, the average annual Western U.S. wildfire season is now 105 days longer, has three times as many large fires (larger than 1000 acres), and burns more than six times as many acres.5

    According to the 2014 National Climate Assessment, warming temperatures and drier conditions are major factors resulting in the increase in wildfires; both temperatures and reduced moisture are linked to human-caused climate change and affect the dryness and flammability of landscapes, measured by scientists as fuel aridity.6 High levels of fuel aridity can provide large areas conducive for the spread of wildfire once ignited.

    According to one study that looked at eight fuel aridity metrics in the Western U.S. and modeled climate change’s effects on them, human-caused climate change accounted for about 55 percent of the observed increases in fuel aridity between 1979 and 2015 (Figure 6), and added an estimated 4.2 million hectares of forest fire area between 1984 and 2015.7 Based on all eight metrics, the Western U.S. experienced an average of 9 additional days per year of high fire potential due to climate change between 2000 and 2015, a 50 percent increase from the baseline of 17 days per year when looking back to 1979. The correlation between fuel aridity and forest fire area each year was found to be highly significant (R2 = 0.75) for 1984 to 2015.

    One of the eight metrics analyzed by the study is the Keetch-Byram drought index (KBDI), a measure of the dryness of the top 8 inches of the forest floor on a scale from 0 to 800. Lower numbers on the scale indicate a higher moisture level on the forest floor and higher numbers on the scale indicate more severe drought and thus higher wildfire potential.

    Previous Climate Central research found that under a high-pollution future scenario (i.e., RCP8.5), California would experience an additional 24 days per year with a KBDI value of 600 (the level at which the potential for wildfires is high) or above by 2050.5 The only state with a greater increase in the number of days with high KBDI values is Arizona, at 34 additional days.

    Ecosystem changes and natural climatic variation can also have large influences on wildfire seasons. Even without human-caused climate change, wildfires would have increased in many regions due to other human activities and natural factors. In particular, although wildfires are a natural process in Western ecosystems, their roles in keeping forests in healthy condition have not been well understood, and so they are often extinguished as quickly as possible. As a result of strenuous efforts to suppress wildfire and other land-management practices such as livestock grazing, logging, and land-type conversion,8,9 many forests have experienced fire deficits, becoming overgrown and littered with flammable material such as leaf litter and saplings. Wildfires that break out during fire deficits can be unnaturally large and severe.10-12 In addition, the introduction of non-native species, especially invasive grasses, can have significant impacts on grassland wildfires as these plants can provide fuel for fires.13

    Wildfire Smoke and Health

    One of the greatest concerns with wildfires is their impact on air quality and associated health consequences; PM2.5  is just one of the pollutants in wildfire smoke, but its small size makes it a well-known threat to people’s health. Californians are at particular risk from wildfire-related health impacts, because the state has the largest population in the U.S. living in wildland-urban interface (inhabited areas approaching wildland areas) where there is an elevated risk of being exposed to wildfires.14 More than 11 million people, about 30 percent of the California population, live in these wildland-urban interfaces.5

    To explore specific linkages between wildfire smoke and health, Liu et al. (2016) developed the concept of “smoke-wave” days, defined as two or more days in a row with wildfire-specific PM2.5  concentrations above 20µg/m3 (the 98th quantile of wildfire-specific PM2.5 concentrations in the study area).15 In Liu et al. 2017, smoke wave days matched satellite (MODIS) records of large wildfires and the researchers found that as smoke-wave day intensity increased, respiratory admissions to hospitals increased.16 In particular, smoke-wave days with PM2.5  concentrations above 37µg/m3 (the 99.5th quantile) were associated with a 7.2 percent increase in respiratory related admissions to hospitals compared to non-smoke wave days. Cardiovascular admissions tended to be highest during the first two days of a smoke-wave and then decrease, while respiratory admissions exhibited the opposite trend, increasing as the days go by.16

    These findings are consistent with other studies, as highlighted in a critical review of the literature on the health impacts of wildfires published in 2016 by Reid et al.17 Various respiratory problems in asthmatics and non-asthmatics alike, measured by physician visits, emergency department visits, and hospitalizations were found to be strongly associated with wildfire smoke exposure as well as significant declines in lung function for those without asthma.17

    Included in the review analysis is one study that looks at how measures of community health modified health outcomes from a wildfire in North Carolina. The study found that health effects of wildfire pollution are significantly associated with poverty and income inequality.18 The study first finds that per 100µg/m3 of PM2.5 exposure, there was a 66 percent increase for hospital visits related to asthma on the day of exposure, and a 42 percent increase in visits related to congestive heart failure (CHF) the day after exposure.

    The study also finds that those counties ranked lowest on the 2010 County Health Rankings for North Carolina (a measure of overall community health based on specific determinants of community health, such as education, income, access to clinical care, diet and exercise) had significantly higher relative risks of asthma on the days of and immediately after wildfire-associated PM2.5 exposure than those counties ranked highest. Of the factors examined that combine to create the County Health Rankings, the counties ranked lowest for poverty, measured as the number of children below the poverty line, had twice the relative risk of asthma as an outcome from PM2.5 exposure than those counties ranked highest (the largest difference). Counties with the greatest income inequality had 223 percent higher risks of CHF as a health outcome from wildfire pollution.

    Wildfire smoke can travel and affect communities hundreds of miles away from its source. The North Bay Fires affected air quality in the Central Valley and satellite images show it traveled more than 500 miles over the Pacific, reaching as far south as Mexico.19 In 2015, smoke from wildfires in central Canada resulted in multiple days of exceedances of EPA standards in Maryland.20 In 2002, wildfire smoke from fires in Quebec impacted populations all along the East Coast of the United States, and a nearly 50 percent increase in hospital admissions for respiratory diagnoses for the elderly was associated with the smoke plume and concurrent PM2.5 in counties in states between New York and Washington, DC.21

    The decades of work that have gone into reducing PM2.5 through environmental regulations and technological improvements are being undermined by the West’s worsening wildfire seasons, with large wildfires being amplified by higher temperatures and drier conditions associated with human-caused climate change.


    Air quality data was acquired from the California Air Resources Board’s query tool site. For the multiyear time series the following selections were made for the Sacramento Valley and San Joaquin Valley Air Basins:  PM2.5, daily average, year-at-a-glance. The total number of exceedances, labeled on the site in red, were tallied for the yearly total exceedances. Then the number of exceedances during June, July, August, and September were tallied for peak wildfire season exceedances. The ratio of these two numbers gives the fraction of annual exceedances occurring during wildfire season. This was repeated for all available years for which >95% of the days in a year had a measurement available, which was 2000 to 2016. Linear regression fits to these data were calculated using the R Statistical Software package.22  The data for the San Francisco Bay air basin was queried in a similar manner as above, but instead of recording days above the federal standard the daily average concentrations at the highest monitoring site in the basin are reported by month through October 2017.

    About this project

    Climate Central is a nonpartisan and non-advocacy nonprofit based in New Jersey that researches and reports on the changing climate. This report was written by Research and Communications Fellow Julia Langer. Data analysis by Climate Scientist Todd Sanford, Ph.D. Additional research by Features Journalist John Upton. Graphics by Multimedia Designer Megan Martin.

    Please direct queries to

    “Breathing Fire,” a feature article about wildfire pollution written by John Upton and produced in partnership with Kaiser Health News with support from the Bill Lane Center for the American West at Stanford University, can be read on Climate Central’s website and elsewhere.

    We gratefully acknowledge John Abatzoglou (University of Idaho), Ana Rappold (EPA), and Jia Coco Liu (Yale University) for reviewing the analysis and providing helpful feedback on an earlier version of this report, and Loretta Mickley (Johns Hopkins) and Colleen Reid (University of Colorado, Boulder) for providing feedback on an earlier version of the report. 


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