The Science of Wildfires
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The Science of Wildfires

Did you know that trees contain the same kind
of compound as gasoline? It’s true! When wood is heated to about 150 degrees Celsius,
its cells start to break down and release volatile gases. You know these gases as smoke. But they’re
actually full of hydrocarbons — the same kind of molecule that you find in other fuels,
like octane and methane. When they’re heated up enough, hydrocarbons
ignite easily, and burn really well. So if that smoking wood gets even hotter,
those gases react quickly with the oxygen in the air and combust to form flames! That, friends, Chemistry of Fire 101, and
it’s responsible for more than 100,000 uncontrolled chemical reactions — more commonly known
as wildfires — in the U.S. that together consume up to 3 million hectares of forest
and brush every year. That’s an area about the size of Maryland,
burning annually. However, that’s not entirely a bad thing
— fire serves a lot of important ecological purposes, and many ecosystems have adapted
to make the most of it. The problem is that it’s fire’s job to
destroy things, and when that encroaches on human territory, which is pretty much everywhere,
we have a problem. Wildfires really are an amazing force of nature:
They can leap across highways, create their own wind, and in certain conditions, move
at speeds exceeding 30 kilometers per hour. Yeah, that’s probably faster than you can
run. And scientists are beginning to find changes
in how and where wildfires are occurring: Truth be told: They’re getting bigger, and
fast. [Intro] It makes sense when you think about it, but
every fire requires three things: heat, oxygen and fuel. Foresters know this as the fire triangle,
and wildfires will always spread in the direction that has the most abundant of these three
elements. Likewise, the only way to put a fire OUT is
to eliminate, or at least significantly limit, one of these things. The source of heat that starts a fire can
be either natural or not — like lightning, a match, or an ember from a camp fire. But which fuel actually ignites from this
heat depends on a number of factors, including its moisture content, how much of it there
is, even how it happens to be spread out over the environment. Lighter fuels — like grasses, leaves and
needles — tend to dry out quickly and burn quickly. Heavy fuels, like the branches and trunks
of a tree, will take longer to warm and ignite. Either way, it’s really the quantity of
fuel that determines whether a fire can spread. And how about oxygen, the third point on the
triangle? Well, air is made up of about 21% oxygen, and most fires require only at least
16% oxygen to get started, and keep going. Put together, these three elements combine
to form one of nature’s most powerful, important, and transformative forces. Because, even though we typically think of
fire in terms of what it destroys, many ecosystems depend on it for renewal and maintenance. On grasslands, fires promote the growth of
herbs and grasses, and prevent trees and non-native plants from crowding them out. And fire has been such constant part of forest
ecosystems that a bunch of species have actually adapted to take full advantage of it. There’s the jackpine, for instance: Its cones
open when exposed to the intense heat from a fire, dropping its seeds into the ash-enriched
soil. Every single living jackpine can die in the
fire, but this adaptation makes sure that new ones will grow in their place. Forest fires also tend to stimulate the flowering
and fruiting of many plants. And that’s because wood ash is one of the
best fertilizers around — it contains just about all of the nutrients that soils supply
for plant growth, including calcium, potassium and magnesium. And ash also acts a liming agent, because
of the carbonates that remain after wood burns. This raises the pH to help neutralize acidic
soils. Fires also remove much, if not all, of the
canopy — the uppermost layer of the forest. With that overhead cover gone, sunlight and
rainfall can make their way to the forest floor. A nice, open canopy can encourage other grasses
and wildflowers to take hold, while reducing the competition for water and nutrients in
the soil. So, I mean, what’s not to love about fire? Oh, yeah! The destruction! We like to call them natural disasters, but
wildfires are almost always the result of human behavior. According to the U.S. National Park Service,
nearly 90% of all wildland fires in the U.S. are caused by people, whether by illegal or
unattended campfires, discarded cigarettes, or arson. Even sparks from power equipment and fallen
power lines have been known to cause forest fires. But the remaining 10% of fires are the result
of nature — almost always a lightning strike, or, in much rarer cases, lava, if a volcano
happens to be nearby. Now, for decades, scientists have been studying
fire behavior, in the hopes of better understanding these notoriously unpredictable natural phenomena. And it’s a complicated science. Weather
is obviously a major factor here, whether it be wind, temperature or humidity. Wind can not only push flames toward new fuel
sources, it can also create more fuel by drying materials in moist areas. And as I mentioned, fires can actually generate
their own wind, with the upwelling of hot air that they create. This allows fresh air
to fill the vacuum left behind, providing a new supply of oxygen. Things like sunlight and temperature can also
help drive a fire. During the day, sunlight heats the ground and the warm air rises, allowing
air currents to travel up sloped landscapes. At night, the process is reversed — the ground
cools and the air currents travel downward. As a result, fires often burn upslope in the
day and downslope at night. Meanwhile, high humidity levels may be annoying
for humans, but the extra moisture in the air can actually slow the spread of flames
by dampening the fuel. Fires tend to burn less intensely at night because that’s when
the humidity is usually higher. Understanding factors like these has made
us better at combating, and preventing, wildfires. Because, after all, we can’t always let
nature takes its course. Fighting fires means eliminating one piece
of the fire triangle, and the easiest piece for us to control is the fuel. So, firefighting isn’t always a matter of
putting the fire out — instead it can just be a matter of finding a way for the fire
to run out of fuel. To get in front of the threat, foresters often
turn to prescribed burning, where fires are intentionally lit before the dry season, to
remove the dead wood and other fuel. Firefighters will also use this strategy during a fire,
setting blazes to destroy the fuel supply before the wildfire arrives. And of course, there’s water. Now I don’t
know if you know this, but water’s really good at putting fires out. Water attacks all three parts of the fire
triangle — it dampens wood and grasses, helping to reduce their usefulness as fuel; it cools
things down, both on the ground and in the air, reducing the amount of heat; and it helps
block oxygen, mainly by creating steam in the air that helps push the oxygen away. However, water evaporates quickly, especially
when a nice, hot fire is around. So firefighters add things like gels to create what is basically
sticky water that smothers fuels while also cooling them down. This mixture, or slurry,
is often dropped from helicopters or airplanes. Some companies even throw in a dash of fertilizer
to boost plants’ recovery after the fire, and dye it red so pilots can see where it’s
been dropped. But one important lesson that we’ve learned
about fighting fires, is when not to fight them. For most of the 20th century, foresters, at
least in the U.S., tried to put out as many fires as they could, as fast as they could.
And as a result, forests became overgrown, with more small trees and shrubs below the
canopy than you’d normally find with a natural fire cycle. So as a result, frequent, smaller fires have
been replaced by megafires that are larger, hotter, and more severe. A study by the American Geophysical Union
found that the number of large forest fires in 17 Western states increased by about 7
per year between 1984 and 2011. And the total area that these fires burned increased by
more than 36,000 hectares each year. But, as you might guess, the growing severity
of forest fires isn’t just the result of decades-old policy. Climate change is playing
a larger role than ever. Our warming climate is causing higher temperatures,
widespread drought, and earlier snowmelt, which causes earlier spring growth. It also allows infestations of insects, like
winged bark beetles, to expand into new regions where they once couldn’t survive. More infestations
means more dead trees, and more dead trees means more fuel. All of these factors put together may explain
why, in the U.S., the seven most severe fire seasons since 1960 have all occurred after
the year 2000. And it’s not just in the U.S., the outlook
is looking pretty much the same elsewhere in the world. Recent studies predict that drier places in
the middle latitudes and Australia will likely experience more fires in the long term. And
not only that, but places at higher latitudes may also be at greater risk as time goes on.
And that is because those places tend to have lots of carbon-rich peat soil, which can burn
as long and as hot as coal. I am certainly not looking forward to the
day when wild-peat fires above the Arctic Circle become a regular thing. Thank you for watching this SciShow Infusion
— especially our Subbable subscribers. To learn how you can support us in exploring
the world, just go to And as always, don’t forget to go to
and subscribe!

100 thoughts on “The Science of Wildfires

  1. I feel like SciShow tends to have a "greenwashing" approach in some cases. Why they don't tackle the issue of CO2 emissions caused by wildfires? It's nearly a fifth of the total manmade emissions. Forest regeneration is a feeble positive side in comparison to that.

  2. This was a VERY informative video and it is pretty dense too. This is a great video for school revision and I would highly recommend others to watch it as well.

  3. Yeah here in Canada I sometimes wonder how anything can be left in British Columbia because it seams to always be on fire. There was one year where a fire there was so big that it covered all of lower Canada in smoke. The days were dark and people tried staying indoors. If you had to go outside, you but on a mask.

  4. Watch the following video for a SERIOUS suggestion as to how to quell wildfires all over the entire Mountain and Pacific time zones.

    "California Firefighters Over 8,000 firefighters battling over 20 wildfires in California".

  5. I know a lot of you don't believe in God here but I think this is a natural process that cleans the earth and God has arranged it that way. We see the result of interfering with it.

  6. First video ever seen in this channel……………………………………………………………………………………………………………………………………………………………………………………………………………………………………….
    ……….. I love it!! Clicked the subscribe button

  7. I once met a forest firefighter who told our group of 16 year old junior rangers that if they were to encounter a forest fire, their best bet was to run into the forest fire as no one could outrun them. And that they would be safe on the other side. Im now wondering if he hated teens.

  8. One of the coolest things about large fires is their ability to create their own weather systems. (Yeah, they actually try to teach us firefighters science, heh. We don't just hike and smack the ground with tools all the time.)
    The smoke plume of large fires can produce thunderstorms, which ignite small fires in front of the head of the main fire via lightning. In an unstable atmosphere firewhirls can grow very large. In '14 there was a F1 scale tornado made out of fire in N. Cal that snapped Doug Fir like toothpicks.
    It's also pretty hard for people to understand why we light the forest on fire to stop forest fires. We spend a lot of our time lighting shit on fire – it's like legal arson. Greatest job in the world. 😛

  9. Oh, okay. A wildfire is faster than me and it can follow me up and down hills. Anybody know any good deals on house-boats?

  10. every time they say 90% of forest fires are caused by humans I wonder how much that was in prehistory because we've controlled fire for a while and it's possible that nature adapted to our carelessness with it

  11. This video was shown in my fire fighting training course. I think I was the only guy there that had watched some of your videos beforehand.

  12. As a fire educator at the University of Idaho I appreciated this positive shout out to fire. We need more things like this. My only complaint is that the image of a "dense" forest was of a bald cypress swamp that does not burn often anyway. With so many stock images of crowded pine stands I am not sure why that was used.

  13. The 2009 Kinglake fire in Australia reached 1000 degrees Celsius and traveled at 40 km an hour. Due to a wind change it reached a 100km fire front (width)

  14. No mention of how the tree huggers shut down logging. State and Federal lands used to sell the trees (fuel) to logging companies. They would remove the fuel and then burn the branches and brush (controlled burning). I bet you will find most of the clean air acts that eliminated slash and burn logging passed just a few years before massive wild fires started happening. Less income for land managing agencies, fewer jobs, and in the end the trees are not saved and air quality is worse.

  15. This video was very helpful in understanding wildfires. I just watched Only the Brave and was wondering why they occurred.

  16. You not about to convince me it's any good in forest fires after saying 90% of them are started by humans like forest fires is something that supposed to happen by seeking benefits of the fire

  17. You nerd, you forgot to inform the public about decades long Chemtrails sprayings as both dessicants and as incendiaries, dual desirable properties that promote heat and super-high temperatures and strongly promote wildfires once they can become initiated. All they did is spray the reactants separately so that the layers mix nicely on the plants and homes to where a thermal incendiary Thermitic type of reaction will only occurr when, for example a laser beam from a satellite or manned satellite or from an overflying jet that can accurately thermal laser anything he can aim at. Using scientific deduction one can conclude that incendiary caliber fires could cause the home levelling effects of thermitically-based fires and heat and temperatures, to melt all the metals, to incinerate cinder blocks, to incinerate roofing tiles with extraordinary resistance to heat and high temperatures, to incinerate red clay bricks in home walls, to melt the wheels and engines of nearby parked cars and motor vehicles, just like in the incineration of the vehicles on 911 and at the Oklahoma City Bombing(S), all super high temperatures events, all were proven incendiary thermal events and nature, 1000s of degrees Celsius…hot enough to melt or incinerate materials that under house fire conditions do not melt or incinerate.
    Only incendiary-based fires could destroy the homes as they did, level with the foundations…..

  18. But what if the firefighters start another fire trying to burn the fuel source for the first fire..idk I'm stoned.

  19. So can anyone point me to a video where a tree gets to 150 degrees+ and randomly combusts starting a “wild” fire?

  20. I'm just here because of my what in the world homework.
    My teacher wants me to watch all of this so I can get information and list what I know

  21. I'm an 18 year old Native American and I've completed my rookie year of wildland firefighting this summer. How many of you 20 year old "adults" can say they served a job that has a purpose?

  22. Poor video. Thumbs down. The narrator entirely neglects to discuss increased fire FREQUENCY and the effects on ecology.
    There some mention here:

  23. S 130/190 prep anyone. I can’t be the only guy here to not sound like a total tool during my red card class

  24. Rx fires literally here. Even some of our native plants won't grow without reaching sufficient heat first. But, being the lightning capitol of the world, that naturally occurs often enough without carelessness.

  25. The number of trees is not the problem. Instead, the type are. Deciduous hardwoods are less likely to burn than conifers. Dense forests are actually cooler, more humid, and less windy.

  26. "wildfires will always move in the direction that has the most abundant (of the 3 elements of the fire triangle)" @1:35 Fire will ALWAYS move in that direction? I knew about the fire triangle's existence since, well, decades ago but… ALWAYS move in that direction?!? Really?

  27. who's watching in 2019, while the freaking rainforest is burning ? Pretty scarry to see a 4 year old video that speaks about current events as far off disasterous times.

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