Wildfires are unplanned, uncontrolled and unpredictable. Here's what you need to know.
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Wildfires have
occurred on our planet ever since terrestrial plants started appearing over 400
million years ago, in the period of Earth’s history known as the Silurian.
While certain regions
are well known for them, such as Australia, Greece, the Amazon and the western
USA, they actually take place on most areas of land around the globe. Wildfires
can even occur in some of the most unexpected places, such as the Arctic
Circle, where so-called ‘zombie fires’ can burn peat and permafrost under the
ice, persisting throughout the cold seasons.
The more well-known
events, such as the devastating fires in Turkey last summer, are generally
associated with the fast burning of large areas of forests. These can be
clearly seen as smoke plumes from a distance, and are even visible from space.
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Wildfires can wreak
havoc on everything in their path, be it humans, animals or buildings. In some
parts of the world, the loss in biodiversity can be catastrophic. But in other
cases, the natural occurrence of wildfires is so ingrained that some species
have evolved to work with it. For example, some plants’ seeds require exposure
to fire in order to sprout.
What are the
conditions for a wildfire to start?
Wildfires start when
the vegetation is ignited, with drier vegetation making this process much
easier. The ignition can be either human-caused (from barbecues, arson, or
discarded cigarettes) or natural (from lightning strikes or volcanic eruptions,
for example). A lot of fires are caused by humans, which is why many countries
have laws on what months people are allowed to have a barbecue, even on their
own property.
These things on their
own are not normally enough to allow the fire to spread. The moisture
accumulation over the preceding months, especially in soils, can help prevent
spread. Likewise, the current humidity, or whether or not it is raining, is
also critical. In some countries where wildfires spread rapidly, it is the wind
that is doing the real damage – fuelling the fire with replenished oxygen,
pushing the flames to adjacent vegetation, and spreading burning embers far and
wide.
Forest fires can
sometimes reach speeds of up to 11km/h, with smoke being particularly
disorientating for anything in the vicinity of the fire.
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Is climate change the
biggest factor to changes in wildfires?
Despite climate change
leading to an increased risk of wildfires, satellite data from the 1990s
onwards has actually shown that the global area burnt from wildfires has gone
down. A large part of this decrease is due to forested areas being converted to
farmland. It is therefore known that societal interventions are at least as
important for wildfires as climate change is, but for many regions around the
world, the interplay between each factor is not clear.
For some particularly
well-studied hotspots, such as western North America, there is strong evidence
that supports climate change as the dominant driver of the increases in burnt
land. But for most other regions around the globe, this is not the case, and it
is believed that natural climate cycles, deforestation, fire suppression and
agricultural burning can play a more dominant role.
The human
interventions here can be particularly important if the right policies are in
place, and the more that climate change leads to increases in wildfires, the
more we will need these societal interventions to combat that.
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Are fires changing due
to climate change?
Given the different
weather types that influence fire risk, the links with climate change are
complex. For many active wildfire regions around the world, fire risk is
projected to increase, mainly driven by elevated temperatures, but also from
decreasing humidity. This combination is ideal for drying out vegetation,
creating the perfect fuel for the fires.
Wildfires tend to
occur in summer, where temperatures are highest, but what goes on in the
earlier seasons can also be important. The amount of vegetation, or fuel, is
also critical, and we expect this to increase for many parts of the world, as
atmospheric carbon dioxide makes plant photosynthesis (and therefore growth)
more efficient.
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Even today, and all
else being equal, it is believed that climate change could be doubling the land
that is being burned from wildfires. On around a quarter of vegetated land, the
wildfire season has also increased, due to a combination of increasing droughts
and raised temperatures.
When trees burn, they
release their stored carbon into the atmosphere, and this can cause up to a
third of ecosystem carbon emissions. This is a vicious negative feedback cycle,
whereby climate change is causing more wildfires, which in turn leads to more
climate change.
Source:
https://www.sciencefocus.com/planet-earth/wildfires/
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