Inferno on Earth: Wildfires Spreading as Temperatures Rise

Inferno on Earth: Wildfires Spreading as Temperatures Rise

19 November 2009

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Global– Future firefighters have their work cut out for them. Perhaps nowhere does this hit home harder than in Australia, where in early 2009 a persistent drought, high winds, and record high temperatures set the stage for the worst wildfire in the country’s history. On February 9th, now known as “Black Saturday,” the mercury in Melbourne topped 115 degrees Fahrenheit (46.4 degrees Celsius) as fires burned over 1 million acres in the state of Victoria—destroying more than 2,000 homes and killing more than 170 people, tens of thousands of cattle and sheep, and 1 million native animals.

Even as more people move into fire-prone wildlands around the world, the intense droughts and higher temperatures that come with global warming are likely to make fires more frequent and severe in many areas. (Seetable of regional observations and predictions.) For southeastern Australia, home to much of the country’s population, climate change could triple the number of extreme fire risk days by 2050.

Although fires typically make the news only when they grow large and put lives or property at risk, on any given day thousands of wildfires burn worldwide. Fire is a natural and important process in many ecosystems, clearing the land and recycling organic matter into the soil. Some 40 percent of the earth’s land is covered with fire-prone vegetation. A number of plants—such as giant Sequoia trees and certain prairie grasses—need fire to propagate or to create the right conditions for them to flourish.

Fire patterns have changed over time as human populations have grown and altered landscapes by clearing forests, allowing pasture animals to overgraze grasslands, and importing new plant species. Across parts of the western United States, for example, cheatgrass, an invasive annual adapted to frequent burns, has supplanted native brush, desert shrub, and perennial grasses that typically experience longer intervals between fires. In other areas, mixed-age and mixed-species forests have been replaced by single-species plantations where flames can jump easily from tree to tree. The result, instead of a low-intensity restorative fire, is a fire so hot that it can cause lasting harm to soils.

Humans have also altered fire patterns through deliberate suppression. After 1910, when a severe wildfire charred more than 3 million acres of western U.S. forest in just two days, the strong desire to protect timber resources gave life to a policy of quickly extinguishing fires. For decades firefighters proved remarkably successful in this endeavor, but the upshot was that forests became so loaded with fuel that a blaze that evaded control could quickly grow into a dangerous megafire.

Now policies are shifting in many places to let some fires proceed naturally or through preventative controlled burns; yet by warming the planet, we may be relinquishing even more control than we bargained for. Higher average global temperatures mean extremes are in store: even as climate change brings more flooding in some areas, other places will be plagued by droughts and extended heat waves. As the temperature rose between the 1970s and early 2000s, for instance, the share of total global land area experiencing very dry conditions doubled from less than 15 percent to close to 30 percent. A hotter, drier world burns more readily. Global warming could be pushing us into a new regime of larger, longer-burning, more intense fires as well as fires in places that historically have been hard to ignite, like moist tropical forests.

Already there is evidence of the connection between higher temperatures and wildfire. Anthony Westerling of Scripps Institution and colleagues found a marked uptick in forest fires in the western United States since the mid-1980s, with the wildfire season lengthening by 78 days over the last 15 years compared with the preceding 15 years. The fire season length and the duration of each fire rose in concert with regional spring and summer temperatures, which were an average 0.87 degrees Celsius higher in the later period. Higher temperatures are melting mountain snow cover earlier in the spring, leaving less moisture for the summer and giving fires a better chance to spread. And while human land use certainly has had a direct effect on wildfire patterns throughout the West, the biggest increase in U.S. wildfire frequency has actually occurred in the largely untouched mid-elevation Northern Rockies forests, implicating climate change.

Farther north, Alaska’s and Canada’s boreal forests recently have experienced more-frequent fires, releasing enough carbon to transform them in some years from net absorbers to net emitters. Between the 1960s and the 1990s, the total area burned more than doubled.  Higher temperatures have extended the range of the tree-damaging spruce budworm into new territory and allowed spruce beetles, no longer delayed by cold winters, to complete their typical two-year life cycle in just a single year. Drought has limited the efficacy of the trees’ defenses. Together the insects and the drought are leaving millions of acres of dead wood in their wake, providing fuel for wildfires. Overall, a warmer climate is predicted to double the area burned in northern Canada by 2100; in Alaska, the area could double by as early as 2050.

In other parts of the world fire regimes are changing and are projected to change even more as the planet heats up. Over much of Europe fire frequency decreased during most of the twentieth century, and expanding forests soaked up carbon.  Now, however, some areas may be starting to see more fires. Between 2000 and 2006, some 50,000 fires burned each year in the Mediterranean region, compared with 30,000 a year in the 1980s, though the total area burned did not increase, in part because of more vigilant firefighting.

During Europe’s record 2003 heat wave, which killed over 50,000 people, an estimated 650,000 hectares of forest burned continent-wide. Although the number of fires during this warm and dry year was not particularly high, the area burned was a record. More than 5 percent of Portugal’s forest area burned, four times the 1980–2004 annual average, resulting in economic damages exceeding 1 billion euros. If future warming is not kept in check, hot and dry summers like 2003 could happen as frequently as every other year, dramatically increasing wildfire risk.

For Southeast Asia, the extreme 1997–98 El Niño brought a major drought to the region, allowing some of the most severe fires in recent history to burn in Indonesia, the Philippines, and Laos. Fires set to clear land jumped from grasslands and shrublands to logged forests and peat swamps, where they burned underground. For months Southeast Asian skies were hazy from smoke. Nearly 10 million hectares burned in Indonesia alone, affecting 23 of 27 provinces and costing more than $9 billion.

During that same El Niño, more than 20 million hectares burned in Latin America, wreaking damages of up to $15 billion. In 2001 the following El Niño brought more drought and put a frightening one third of Amazon forests at risk of burning. With a temperature rise of more than 3 degrees Celsius—well within the range projected for this century barring rapid and dramatic action to curb carbon emissions—much of South America is likely to see more frequent wildfires.

Just as a weakened immune system leaves a person vulnerable to otherwise innocuous germs, the combination of logging, road construction, and intentional burning to clear forests for cattle ranches, farms, and plantations has fragmented the world’s tropical forests, increasing their vulnerability to fire. Piling higher temperatures on top of such stresses could completely undermine forests’ resilience. For the massive Amazon rainforest, we risk reaching a tipping point where recurrent droughts dry out the landscape enough so that small fires can turn into devastating conflagrations.

We all rely on trees to soak up greenhouse gases and store carbon. If large swaths of forest go up in flames, it could set into motion a vicious cycle, where more wildfires in turn release more carbon into the atmosphere. Stabilizing climate, and doing so quickly, takes on a new urgency when it means averting an inferno on earth.

Wildfires by Region: Observations and Future Prospects  AreaObservationsFuture Prospects   WORLDWIDE   Around the world, somewhere between 75 million and 820 million hectares of land burn each year. The Intergovernmental Panel on Climate Change states that “climate variability is often the dominant factor affecting large wildfires” despite widespread management practices aimed at reducing flammable materials in forests. Wildfires (not including fires intentionally set to clear land) burn some 3–8 percent of total terrestrial net primary productivity annually, releasing on average 1.7–4.1 gigatons of carbon into the atmosphere.Global warming will alter fire regimes. Climate models predict that higher temperatures and longer droughts will increase wildfire frequency, particularly in semi-arid regions. Higher rainfall in some areas could reduce fire frequency, though it could also foster more vegetation, thus providing more fuel for fires. Lightning, an important ignition source, is thought to increase in a warmer climate, and more-intense rainstorms could exacerbate post-fire runoff and landslides. Fire is expected to grow as a source of carbon dioxide.   AFRICA  Sub-Saharan AfricaSome 54 percent of all fires occur in Africa, with hotspots in Northern Angola and the southern Democratic Republic of the Congo, as well as southern Sudan and the Central African Republic. In these areas, grasslands and fields (which have largely replaced the tropical forests that were deforested decades ago) burn more readily, prohibiting forest regrowth.Increased fires are predicted as temperatures rise in the Sahel and southern Africa. Places affected by desertification will likely see fewer fires because of lack of vegetation to burn.Tropical AfricaAn estimated 70 percent of all forest fires occur in the tropics, with half of these in Africa. Recent El Niño events may have expanded the area burned in tropical Africa. Some models forecast reduced fire frequency in tropical Africa because of the regional wetter conditions projected with increased global temperatures.   EUROPE  Northern, Central, and Eastern EuropeOver much of the continent, fire frequency has been decreasing, in part due to increased suppression efforts, contributing to the carbon land sink. However, some areas have started to see a change in fire patterns. Between 1965 and 1998, for instance, England and Wales have had warmer and drier summers and more fires.For Central and Eastern Europe, summer precipitation is projected to decline, increasing water stress. “Catastrophic” peatland fires are projected to occur more frequently during dry years. Fire danger is likely to rise, though less than in Southern Europe.Southern / Mediterranean EuropeLarge swaths of forests have burned during recent droughts and heat waves. During the record 2003 heatwave, fires consumed some 650,000 hectares of forest, mostly in the south. This hot and dry year was a record in terms of fire area but not incidence. More than 5 percent of Portugal’s forest area burned, four times the 1980-2004 average, resulting in economic damages exceeding 1 billion euros. Between 2000 and 2006 an average of 50,000 fires burned each year across the Mediterranean region, compared with 30,000 per year in the 1980s.High temperatures and drought are projected, along with an increase in the frequency of wildfires. Hot and dry summers like 2003 are likely to become more common in a warmer world; some scenarios project that by 2080 such conditions could arise every other year. For a 1.0–2.8 degrees Celsius rise in temperature above preindustrial levels, most areas will experience an 8–20 percent increase in fire risk periods lasting a week or more. Fire season across the Mediterranean region is expected to lengthen by a month, and fires are predicted to occur more frequently, changing forest ecosystems to scrubland.   ASIA  Northern AsiaOver the last decade some 12,000–38,000 fires have burned each year in Asia’s boreal forests, affecting up to 3 million hectares. Higher temperatures in Siberian peatlands and increased human activity are tied to an increase in fires (with 20 million hectares burned in 2003 alone). In Mongolia, the temperature has risen by 1.5 degrees Celsius, and springtime precipitation has fallen by 17 percent over the last 60 years. Over the last 50 years forest and steppe fires have occurred more frequently and have burned larger areas.Climate change is likely to increase the frequency and extent of forest fires, leading to the release of more carbon to the atmosphere.Himalayas and the Tibetan PlateauWhile dry-season fires set for agricultural purposes are common, fires in Nepal in late 2008 and early 2009 became unusually severe because they followed a record dry spell of nearly six months with no precipitation.Fire risk in high elevation areas, like the Tibetan Plateau, is projected to increase at higher global temperatures (with changes becoming more pronounced at increases of more than 3 degrees Celsius above preindustrial levels). Reduced snow and ice coverage will facilitate the spread of fires.Southeast AsiaThe severity and extent of forest fires has increased over the last two decades, associated with intensification of land use on top of higher temperatures and less rainfall. Some 3 million hectares of peatland has burned over the past decade. Some of the most extreme forest fires in recent history burned in Indonesia, the Philippines, and Laos during a major drought associated with the 1997–98 El Niño. These fires mostly were lit by people to clear land, but they spread rapidly because of the extremely dry conditions. In Indonesia alone the fires led to $9 billion in economic losses, including health damage from the smoke, and, according to NASA, “released as many greenhouse gases as all the cars and power plants in Europe emit in an entire year.”Global warming could bring more rainfall to this region, but it is uncertain whether this would outweigh the heightened fire risk from increased temperatures. It is possible that El Niño-type events could increase in frequency and duration in a warmer world, multiplying the conditions that made the 1997–98 fires so severe.    OCEANIA  AustraliaAustralia’s natural vegetation is fire prone, with some areas burning each year. Severe fires are closely linked with droughts and higher temperatures, often associated with El Niño–Southern Oscillation and Indian Ocean Dipole events. In the latter half of the twentieth century, Australia saw a trend toward higher temperatures, longer heat waves, and more dry periods. Drought has persisted for more than a decade in southeastern Australia, setting the stage for catastrophic fires. In February 2009, more than 400,000 hectares in Victoria burned in the country’s worst “natural” disaster in over a century, killing more than 170 people, tens of thousands of livestock, and more than 1 million native animals and destroying more than 2,000 homes. In southwestern Australia the woodland area burned over the last 7 years accounts for more than half of the total 4.5 million hectares burned in the past 36 years. Drought, heat waves, and fire are projected to increase with high certainty. Fire danger is likely to increase because of shorter intervals between fires, increased fire intensity, more rapid fire spread, and fewer fire extinguishments. Southeastern Australia, where much of the population resides, is likely to see the occurrence of extreme fire risk days increase by up to 65 percent by 2020 and up to 300 percent by 2050. Indian Ocean Dipole events, which are tied to lower rainfall and higher temperatures that lead to higher bushfire risk, are also predicted to increase with global warming.   NORTH AMERICA  United States overallSince 1980, some 2.2 million hectares have burned each year, almost double the 1920 to 1980 average. The area burned per fire has also risen.Distinct regional wildfire seasons could start to blur into a year-round phenomenon throughout the United States. More fires could encourage savannas to take over forested areas.Western United StatesAcross the western United States the annual wildfire season has lengthened by 78 days in the last 15 years compared with the previous 15 years, in association with higher temperatures and reduced snowpack. The increase has been the greatest at higher elevations in the Northern Rockies, areas where fire regimes are less likely to have been altered directly by people.The U.S. Forest Service projects that a 1.6-degree Celsius rise in summer could double wildfire area in 11 western states. Alaska and Western CanadaTundra is burning more frequently. Between the 1960s and 1990s, the total area burned in the North American boreal region increased by a factor of 2.5 while the area burned by human-ignited fires did not change. Some of the worst fires on record have come since 2000. With higher temperatures and drought in the 1990s, damaging insects have extended their range into new territory, leaving trees more vulnerable to fire.With warmer temperatures the trends of higher temperature, drought, and insect outbreaks are predicted to worsen. Fire may accelerate ecosystem change between taiga and tundra. By the end of the century, the area burned in parts of Canada’s circumboreal forest could double, and fire occurrence could increase by 50 percent. For Alaska, the area burned could double by mid-century and triple or quadruple by 2100.   LATIN AMERICA  South and Central AmericaFire has traditionally been used to clear land, but fires can spread out of control during droughts. During the 1997–98 El Niño more than 20 million hectares across Latin America burned, resulting in damages of up to $15 billion.More frequent wildfires are likely in much of South America, increasing by some 60 percent with a temperature increase of more than 3 degrees Celsius.AmazoniaWhile the tropical rainforest is typically extremely difficult to ignite, tropical forest fires are becoming more common, extending beyond traditional land clearing. Drought is a major factor: some one third of Amazon forests were at risk of fire during the 2001 El Niño–Southern Oscillation period. Subsequent droughts in 2005 and 2007 brought major fires to the southern Amazon.The higher temperatures and more frequent and longer lasting droughts projected with global warming could subject much of the Amazon to fire vulnerability, setting off a self-reinforcing cycle if major fires release hundreds of millions of tons of greenhouse gases into the atmosphere. Fire could accelerate the transition of forests to savanna.Compiled by Janet Larsen, Earth Policy Institute,, November 2009.Sources include the Intergovernmental Panel on Climate Change. Full citations available on request.

For more background information see:

Global Pyrogeography: the Current and Future Distribution of Wildfire

Fire in the Earth System

The Amazon’s Vicious Cycles: Drought and Fire in the Greenhouse.Ecological and Climatic Tipping Points of the World’s Largest Tropical Rainforest, and Practical Preventive Measures

Warming and Earlier Spring Increase Western U.S. Forest Wildfire Activity

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