Is climate change fanning megafires? | Science News for Students

Is climate change fanning megafires?

As wildfires grow in number and intensity, scientists look for the fingerprints of global warming
Nov 8, 2018 — 6:40 am EST
A nightime photo of a wildfire engulfing a forest across a lake. Everything is tinged bright red and orange from the flames.

Extreme wildfires are becoming more common in many parts of the world.


The biggest fire in California history ignited shortly after noon on July 27, 2018, and burned until mid-September. Called the Mendocino Complex Fire, its twin infernos started at the same time. They also burned close to one another and quickly blazed across forested lands. Together, they charred more than 1,800 square kilometers (700 square miles) — an area nearly half the size of the state of Rhode Island. Ninety crews of firefighters worked to contain it. They used hundreds of fire engines, 20 helicopters, 76 bulldozers and other tools. One firefighter died and four were injured. More than 150 homes burned, and smoke from the fire spread through the sky to nearby states.

Six of the state's worst fires blazed in 2017 and 2018. A wildfire that burned through Napa Valley in October 2017 was particularly bad. Before it ignited, people who lived in the area described incredible winds that could knock a person over. Once the fire started, witnesses saw fires jump across roads, rip through vast fields of grapes and hop over hills. During more than three weeks, the fire claimed 22 lives, destroyed more than 5,000 structures and burned more than 146 square kilometers (56 square miles). That’s an area as big as one-and-a-half Disney Worlds. By year end, 2017 became California’s worst wildfire year on record.

Many areas across the world have seen a rise in extreme fires in recent years. Those include western U.S. states and southern Europe. They also include places you might not expect.

For example, wildfires used to be uncommon on Alaska’s North Slope. This region borders the Arctic Ocean and is home to the largest U.S. oil field. Now, however, fires are igniting there more frequently. The same is true in other Arctic regions. In July, for instance, people had to evacuate cities in northern Sweden as wildfires swept through them.

Some reasons for the rise in destructive fires are clear. People have been building homes on the edge of forests that face a high risk of fire. Periods of heavy rainfall can also spur a massive growth in vegetation. If that same area later experiences a drought — and California has suffered from many droughts in recent years — that new vegetation may dry out and become tinder that burns easily.

“The Napa Valley fires were a good example of this,” said Timothy Brown. He spoke during an online press briefing in August 2018. (It had been organized by a science communication project called SciLine.) During the briefing, experts talked about climate and weather. “Extreme precipitation in the winter and spring allowed for extensive [vegetation] growth,” he noted. “Then, when that dried later in the fall, it became very flammable and susceptible to ignition.” Brown is a climate scientist at the Desert Research Institute in Reno, Nev.

The signal of climate change

Has climate change made wildfires worse and megafires more likely? That’s what Brown and other climate scientists want to know. More importantly, they worry that more intense fires could become the new normal.

Studies have long predicted that warmer temperatures, due to climate change, make droughts and heat waves more likely. Many areas hit by recent fires had suffered through extreme droughts and heat waves.

But connecting individual fires to climate change is complicated. That’s partly because fire is complicated. Blaming climate change for any single fire is too simple. It ignores the natural conditions that make fire possible. But hotter days and warmer nights, caused by changes in the climate, do likely boost the risk of fire.

Scientists are still trying to agree on what makes a blaze ignite and spread. A wildfire has three main ingredients. First, it needs a spark. This can come from lightning or a downed power line. It can also come from negligent or malicious people who set fires by accident or on purpose. Brown points out that people start four out of every five wildfires. Second, a fire needs fuel to burn. This can be the trees in the forest or the dead “litter” — leaves, twigs and grass — on or near the forest floor. Finally, a fire needs weather conditions, like wind and no rain, to help it spread.

Many studies predict that climate change will boost the number of droughts and heat waves. Fire-ravaged areas, including California and Sweden, have had extreme droughts and extreme heat in recent years. Some scientists point to these weather events as proof that climate change makes wildfires worse.

But it’s even more complicated than that, says Janice Coen.

Fires can make their own weather

Coen is a meteorologist at UCAR. That’s the University Corporation for Atmospheric Research in Boulder, Colo. Testing hypotheses about fire is difficult, she explains. After all, scientists can’t go out and start a megafire. But she can make a computer model to test various ideas about the conditions that play a role in them. And that is exactly what Coen and her team did.

California’s 2014 King Fire burned for 27 days. During that time, it destroyed 12 homes. It was started by a man who recorded a selfie of himself right afterward. (He’s now in jail.) Coen wanted to know why the blaze raced so quickly through a forest canyon. To find out, she recreated the fire with a computer program. It used math to study how air particles move. It included data about temperature, humidity, air pressure and wind speeds. Those measurements had been collected by satellites, weather stations and special planes with onboard sensors.

a sattelite image showing smoke from the King Fire in September 2014
Smoke from the King Fire can be seen in this September 17, 2014 satellite image of the border between California and Nevada.
NASA/Wikimedia Commons

These data helped her team explore why the King fire behaved as it did. Laws of physics “tell us what the answer ought to be,” she explains. Those answers can then help scientists predict how future fires will behave.

Some ecologists said the King fire burned so fast and so intensely because it had so much fuel. No fires had burned in that area for years. As a result, leaves and other plant debris had built up on the forest floor. Other researchers blamed the drought. But Coen found yet another culprit: the atmosphere. She reported her findings in the May Ecological Applications.

As a fire burns, it releases heat and water vapor, a gas. As that hot air rises, cooler air is drawn in at the bottom. This process creates a column of rising air. It also creates wind. In the case of the King Fire, those local winds drove the fire into new vegetation — more fuel, Coen’s team reported. As the fire grew, it created more wind, which made the fire more intense. That phenomenon, combined with the shape of the canyon, led to the fire’s rapid spread.   

“Weather directs the fire,” she says. “The fire, in turn, can change the weather.” When she ran the simulated fire without drought conditions, the blaze behaved almost the same way. That suggests the long drought and heat wave had not worsened the fire. Instead, the canyon’s shape and local weather conditions had boosted its intensity.

The terrible fires that have ravaged California in 2018 arose from a complex mix of ingredients. These included the Santa Ana winds, which blow hot and dry through the state every fall. They also included a lack of the rain that usually develops in the cooler months. Less rain may be due to a La Niña event (a natural phenomenon that affects weather patterns worldwide). Some of those ingredients may have been worsened by climate change. But as Coen's study points out, finding some clear fingerprint of climate change in wildfires is not easy.

Power Words

(more about Power Words)

air pressure     The force exerted by the weight of air molecules.

application     A particular use or function of something.

Arctic     A region that falls within the Arctic Circle. The edge of that circle is defined as the northernmost point at which the sun is visible on the northern winter solstice and the southernmost point at which the midnight sun can be seen on the northern summer solstice. The high Arctic is that most northerly third of this region. It’s a region dominated by snow cover much of the year.

Arctic Circle     The northernmost point at which the sun is visible on the northern winter solstice and the southernmost point at which the midnight sun can be seen on the northern summer solstice.

atmosphere     The envelope of gases surrounding Earth or another planet.

behavior     The way something, often a person, other organism or phenomenon acts or conducts itself.

climate     The weather conditions that typically exist in one area, in general, or over a long period.

climate change     Long-term, significant change in the climate of Earth. It can happen naturally or in response to human activities, including the burning of fossil fuels and clearing of forests.

computer model     A program that runs on a computer that creates a model, or simulation, of a real-world feature, phenomenon or event.

computer program     A set of instructions that a computer uses to perform some analysis or computation. The writing of these instructions is known as computer programming.

drought     An extended period of abnormally low rainfall; a shortage of water resulting from this.

ecology      A branch of biology that deals with the relations of organisms to one another and to their physical surroundings. A scientist who works in this field is called an ecologist.

equation     In mathematics, the statement that two quantities are equal. In geometry, equations are often used to determine the shape of a curve or surface.

flammable     Something that can burn (go up in flames) easily.

fuel     Any material that will release energy during a controlled chemical or nuclear reaction.

humidity     A measure of the amount of water vapor in the atmosphere. (Air with a lot of water vapor in it is known as humid.)

ignition     (in chemistry) The act of igniting a fuel in combustion, such as natural gas or gasoline.

La Niña     Extended periods when the surface water around the equator in the eastern Pacific cools for long stretches of time. Scientists will announce the arrival of a La Niña (lah NEEN yah) when the average temperature there drops by at least 0.4° C (0.72° degree F). Impacts on global weather during a La Niña tend to be the reverse of those triggered by an El Niño: Now, Central and South America may face severe droughts while Australia floods.

litter     Material that lies around in the open, having been discarded or left to fall where it may. (in biology) Decaying leaves and other plant matter on the surface of a forest floor.

meteorologist     Someone who studies weather and climate events.

model     A simulation of a real-world event (usually using a computer) that has been developed to predict one or more likely outcomes. Or an individual that is meant to display how something would work in or look on others.

NASA     Short for the National Aeronautics and Space Administration. Created in 1958, this U.S. agency has become a leader in space research and in stimulating public interest in space exploration. It was through NASA that the United States sent people into orbit and ultimately to the moon. It also has sent research craft to study planets and other celestial objects in our solar system.

particle     A minute amount of something.

phenomenon     Something that is surprising or unusual.

physical     (adj.) A term for things that exist in the real world, as opposed to in memories or the imagination. It can also refer to properties of materials that are due to their size and non-chemical interactions (such as when one block slams with force into another).

precipitation      (in meteorology) A term for water falling from the sky. It can be in any form, from rain and sleet to snow or hail.

risk     The chance or mathematical likelihood that some bad thing might happen.

satellite     A moon orbiting a planet or a vehicle or other manufactured object that orbits some celestial body in space.

simulate     To deceive in some way by imitating the form or function of something. A simulated dietary fat, for instance, may deceive the mouth that it has tasted a real fat because it has the same feel on the tongue — without having any calories. A simulated sense of touch may fool the brain into thinking a finger has touched something even though a hand may no longer exists and has been replaced by a synthetic limb. (in computing) To try and imitate the conditions, functions or appearance of something. Computer programs that do this are referred to as simulations.

vegetation     Leafy, green plants. The term refers to the collective community of plants in some area. Typically these do not include tall trees, but instead plants that are shrub height or shorter.

water vapor     Water in its gaseous state, capable of being suspended in the air.

weather     Conditions in the atmosphere at a localized place and a particular time. It is usually described in terms of particular features, such as air pressure, humidity, moisture, any precipitation (rain, snow or ice), temperature and wind speed. Weather constitutes the actual conditions that occur at any time and place. It’s different from climate, which is a description of the conditions that tend to occur in some general region during a particular month or season.


Journal: J.L. Coen et al. Deconstructing the King Megafire. Ecological Applications. Vol. 28, September 2018, p. 1565. doi: 10.1002/eap.1752.