USA — In the immediacy of a raging wildfire, smoke is a tangible, burningpresence. It has a taste and a smell. It can color the world.
But smoke is fleeting, too. When the fires are quenched or the wind shifts,the smoke can seem to vanish.
Elizabeth Davis, 17, photographed smoke billowing from the Poomacha fire on Palomar Mountain Oct. 23. Wildfires generate tons of atmospheric pollutants.Photo: Scott Linnett / Union-Tribune Only it really doesn’t. Rather than ceasing to exist, the smoke may simply havemoved on, physically drifting and chemically shifting toward other, sometimesdistant, places.
You can see it in photos taken last week by NASA’s Terra satellite, orbiting435 miles above the Earth: Plumes of brown-gray smoke from Southern California’swildfires blowing west over the ocean, extending hundreds of miles out to sea.
Where and how far these plumes travel ultimately depends on windcurrents and weather patterns. Some of the smoke may, in fact, blow back,becoming a local health hazard once again.
But scientists see in the plumes an even larger and longer-term problem:global air pollution and its effect on climate change.
There are growing concerns among scientists that fires not just here butaround the world are part of a spiraling and destructive feedback loop: Hot,dry weather caused by climate change increases the frequency and ferocity ofwildfires. These fires release into the atmosphere ever-larger amounts ofparticulates, pollutants and greenhouse gases that, in turn, result in evenhotter, drier weather and more fires.
It’s not unreasonable to argue there’s a connection, said VeerabhadranRamanathan, a noted climate scientist at UCSD’s Scripps Institution ofOceanography.
A photograph taken by NASA’s Terra satellite Oct. 23 showed smoke from the San Diego County wildfires being blown hundreds of miles out to sea. To be sure, the connection is extraordinarily complicated and incompletelyunderstood. Scientists cannot declare Southern California’s wildfires last weekto be the unambiguous consequence of global warming. The fires may, in fact, beprimarily the result of local factors: a years-long drought, abundant fire-pronevegetation and Santa Ana winds, said Anthony Westerling, an assistant professorof environmental engineering at the University of California Merced.
How all of these components fit and work together, said Westerling in astatement with colleagues Thomas Swetnam and Gregg Garfin of the University ofArizona, is not known with sufficient certainty to conclusively link globalwarming with this disaster.
Nonetheless, diverse sources of data gathered here and around the worldsuggest an ill wind is blowing in an alarming direction.
Wildfire smoke is a farrago of burned matter (particulates), gases, vaporsand chemical compounds, the recipe unique to each blaze.
More than 90 percent of the mass of wildfire smoke consists of carbon dioxideand water, but hundreds of other chemicals can be present, among them: carbonmonoxide, mercury, aldehydes, nitrogen oxides, polynuclear aromatic hydrocarbons(PAHs), sulfur dioxide, volatile organic compounds and ozone.
Many of these ingredients pose immediate and obvious health hazards. Smokeparticles smaller than the diameter of a human hair can be inhaled deeply intothe lungs, causing everything from lung irritation to an increased risk ofcancer.
Carbon monoxide (CO) is an odorless, tasteless, invisible poisonous gas.Mercury is an extremely toxic element. Aldehydes are gases that irritate theeyes, nose and mouth. Some forms, like formaldehyde, are carcinogenic, as arePAHs.
Nitrogen oxides are associated with acid rain. In the presence of sunlightand hydrocarbons (organic compounds readily produced in fires), nitrogen oxidescombine to create ozone, a gas that inflames and impairs the lungs and triggersasthma attacks.
These compounds can linger in seemingly clear air for days, even weeks.Perhaps the best cleanser is rain, followed by time and dilution. But theproblem is that the increased frequency and severity of wildfires means thereare more fires billowing more pollutants into the air more of the time.
And they are doing so in enormous amounts.
In 2004, for example, massive wildfires in Alaska and Canada’s YukonTerritory the worst on record scorched more than 11 million acres, anarea roughly the size of the states of New Hampshire and Massachusetts combined.
Scientists monitoring the resulting smoke plumes estimate that the fires fromJune through August produced 30 trillion grams of carbon monoxide an amountequal to all human-generated CO production for the entire continental UnitedStates in the same period. Surface levels of ozone increased as much as 25percent in the northern United States and 10 percent in Europe.
Something similar happened a couple of years earlier when widespread firesroared across western Russia and Siberia, leading to the so-called dirtywinter of 2002-03, when unnaturally high CO and particulate levels hoveredover much of the Northern Hemisphere.
Satellite observations showed the Russian fires had a huge impact on airquality on a global scale, said David Edwards, a researcher at the NationalCenter for Atmospheric Research (NCAR), based in Boulder, Colo.
Wildfires aren’t the only source of airborne pollutants. An estimated 8billion metric tons of dry biomass is burned in vegetation fires each yeararound the world, much of it in fires intentionally set to clear land or oldcrops.
Biomass burns are quite common in the tropics, most associated withagriculture, said Daniel Jacob, an atmospheric scientist at HarvardUniversity.
The result is approximately 4 billion metric tons of carbon released into theatmosphere, the equivalent of about 70 percent of all human fossil-fuelemissions (oil, gas, coal).
Black carbon particulate in the atmosphere causes complex problems. So-calledbrown clouds both absorb sunlight, warming the air, and block it, dimmingthe ocean’s surface and interfering with photosynthesis. The overall effect iscontradictory, but warming seems to be winning.
Ocean temperatures have generally risen over the last 50 years. A studypublished last year found that as seas warmed, growth rates for phytoplankton (microscopicmarine plant life) broadly declined, due perhaps to less photosynthetic activityand less nutrient-mixing in the warmer, stratified water.
Carbon particulate plays a role on land as well. As it settles out of smokeand other forms of air pollution, it can behave like an electric blanket,reducing the albedo, or reflectivity, of the snow while simultaneously warmingit.
When smoke settles on snowy surfaces, it enhances absorption of sunlight,which plays an important role in the retreat of sea ice and melting snowcaps,said Ramanathan at Scripps.
This soot can come from far away. For example, more than 75 percent of theatmosphere-warming, snow-melting soot that falls over the West Coast of theUnited States each spring is delivered by prevailing winds originating in Asia,according to a recent study by Ramanathan.
North America, in turn, sends its air pollution eastward, the jet streamcarrying it over the Atlantic Ocean to Europe.
Dust plays a similar long-distance role. A study earlier this year by theNational Snow and Ice Data Center found that windblown dust fromdrought-stricken or disturbed lands can shorten mountain snow cover hundreds ofmiles away by up to one month.
Virtually all scientists agree that the primary culprits in global warmingare greenhouse gases, such as carbon dioxide (CO2), methane andnitrous oxide. All three gases are abundantly produced by wildfires.
Tom Bonnicksen, a professor emeritus at Texas A&M University, estimatesthe Southern California fires generated 19 million tons of these gases in justthe first three days of burning.
Plant life is among the great absorbers of carbon dioxide, removing thegreenhouse gas from the atmosphere during photosynthesis. But the increasingloss of vegetation worldwide from fires and pollution may skew the process.
In the past, forests have been an important buffer against climate changebecause of the way they absorb carbon, said Johann Georg Goldammer, head ofthe fire ecology research group at the Max Planck Institute for Chemistry inGermany. But warming, bringing more frequent drought and fires, may affectthe balance of the global carbon pool and release extra CO2 into theatmosphere.
As a source of pollutants linked to global air pollution and climate change,human activity is far more problematic than nature. Wildfires tend to beseasonal. Human pollution occurs year-round. The sprawling brown clouds thatblow from Asia (covering the distance in just days) are mostly produced byman-made sources, such as factories and auto exhaust. The situation has onlygotten worse as the economies of China and other countries have grown rapidly.
In 2004, for example, it was estimated that China would surpass the UnitedStates in CO2 production in 20 years. Chinese emissions are nowexpected to exceed American levels this year.
Without doubt, controlling and reducing local pollution sources remains themost pressing issue. You can’t really blame China for air pollution in LosAngeles, said Gabriele Pfister, an atmospheric chemist at NCAR.
But the problem of global air pollution and its implications for climatechange presents a bigger and more burdensome worry for scientists and,arguably, everybody else living on Earth.
The pollutants churned high into the atmosphere by last week’s wildfires posereal and potential hazards, seen and unseen, for anybody downwind. The same canbe said for the billions of tons of chemicals spewed daily into the air by humanactivity around the world.