The 2019-2020 Australian Bushfire Season: Causes and Effects

By Connie Chandler

Global warming is one of the biggest threats to currently face our planet. Each decade since the 1980s has been warmer than all preceding decades on record with a global average temperature 0.61(±0.05) °C higher in the 2010s than the 1961-1998 average (Osborn & Jones, 2020). 2016 holds the record for the hottest year on record with a global average temperature 0.94 °C higher than the 20th century average of 13.9 °C (NOAA, 2017). 2020 only narrowly missed out the record by having an average temperature 0.02 °C cooler than that of 2016 (Thompson, 2020). 

An increase in global temperature by less than one degree may not sound like a huge change, but it takes a huge amount of heat energy to heat up all the oceans, atmospheres and land by this much. For perspective, in the 17th century, global average temperatures were between 1 and 2°C colder than the period between 1951-1980 and this caused the ‘Little Ice Age’. During this time ice was extremely prevalent in the northern hemisphere and in North America there was a great decline in food supplies (Shindell et al., 2001). This rapid increase in global temperature is caused by a range of factors. Most of these factors are either being directly caused by or accelerated by human influence. One of the main factors is known as the ‘Greenhouse Gas Effect’. 

Greenhouse gases (GHGs) are necessary to keep the planet at a habitable temperature. As solar radiation from the sun reaches Earth, it is absorbed by the Earth’s surface and helps to warm it. The Earth then radiates energy as infrared radiation and some of this is absorbed by GHGs such as carbon dioxide and methane in the atmosphere. This in turn causes heat to be redirected back towards the Earth’s surface and cause further heating. The more GHGs that are being trapped in the atmosphere, the more heat is trapped, which is what is leading to these increased global temperatures year after year (Berger & Tricot, 1992). Some of the reasons why there are more GHGs being emitted into the atmosphere are the burning of fossil fuels, deforestation and increased livestock farming (Bueno & Helene, 1991; Grossi et al., 2018; Lelieveld, et al. 2019). 

The effect of these on a global scale means that there is a huge amount of carbon dioxide, nitrous oxide and methane being emitted into the atmosphere and with a lack of vegetation, carbon dioxide cannot be absorbed, and the climate cannot be properly regulated (Solomon et al., 2010). The effects of global warming are being seen more and more frequently around the world in the form of ice melting, ocean acidification and extreme weather events (Bouwer, 2018). One of the most dangerous of these effects that has occurred much more frequently in recent years is fire. These fires are raging over thousands of kilometres for months at a time – much worse than ever before. This was the case for the 2019-20 south-eastern Australian bushfires.

 2019-2020 Australian Bushfires

In previous years, Australia has faced many bushfire seasons, and these can be attributed to several different reasons. The first of these reasons is the overall climate in Australia. Generally, the climate in Australia is hot and dry and can be prone to drought (Hughes, 2003). Being such a large country, the areas in which a bushfire season may occur depends on the time of year as different weather patterns affect different regions of Australia temporally (Ladbrook, 2015). An example of this is bushfire season for New South Wales occurring around spring or early summer, whereas the Northern Territory experiences most fires in winter and spring. Another reason for the existence of bushfire seasons in Australia is the weather. Thunderstorms are common in Australia but due to their climate the associated lightning storms and high wind speeds are considered to be the major natural cause of bushfires around Australia (Dowdy & Mills, 2016). Bushfires can also start through direct human impact. This can occur purposefully through the means of clearing vegetation for land management or accidentally through examples such as barbecues or campfires becoming out of control (Bird et al. 2016; Harris & Lucas, 2019). 

To try and minimise damage, there is existing legislation and policy that states that fires must be regulated and only allowed under a permit (Australian Government, 1999). A reason as to why bushfires can spread so easily in Australia is the nature of the vegetation. To exist, fire requires oxygen, an ignition source and dry fuel. During droughts, vegetation can be very dry and there may be a large amount of fuel load (fallen leaves, branches and bark) that accumulate in the landscape (Russell-Smith et al., 2010). This means that if a fire starts, naturally or through human influence, it can spread very easily. However, considering the natural ecosystems in Australia have evolved with frequent bushfires, many native plant species (e.g., the Eucalyptus) are fire prone and depend on fire to regenerate (Burrows & Middleton, 2016). 

However, the 2019-20 Australian bushfire season was unusually intense and soon became the worst bushfire season that Australia had ever recorded. Known as the ‘Black Summer’, the bushfire season occurred between September 2019 and March 2020 and during this time the fires burnt 186,000 km2 of land, destroying nearly 6000 buildings and killing 34 people (Filkov et al. 2020). In terms of effects on biodiversity it is estimated that nearly 3 billion animals were killed or injured, and many endangered species were driven to extinction (Ward et al. 2020). These fires came at a huge environmental, social and economic cost to Australia. It is estimated that the economic fallout from these bushfires could be as high as $5 billion (Dangar, 2020). Fire is known as one of the most destructive elements seen in nature. This is because it will burn all kinds of vegetation that it encounters and produces many environmentally damaging chemicals such as inorganic ash, sulphur dioxide and nitrogen oxide (Radojevic, 2003). 

During the worst period of the fires, air quality was considered ‘hazardous’ in all southern and eastern states of Australia, causing potential long-term health issues for many Australian people (Vardoulakis et al. 2020). By January 2020, 400 megatonnes of CO2 – a greenhouse gas - had been released into the atmosphere, contributing directly to global warming (Taylor, 2020). As global temperatures increase, droughts and extreme weather events will become more frequent. As these become more frequent, it is much more likely that extreme events such as the 2019-20 Australian bushfire season will become much more common in many places around the world (Dutta et al., 2016). This cycle helps us to see how climate change itself is a huge influence on the cause of these fires. 

How has climate change influenced these fires?

Global Temperatures

Although bushfires of this scale require specific conditions and depend on factors such as rainfall, temperature and humidity in the months preceding the fire event, it has been determined that wildfire events such as the 2019-2020 season in south-eastern Australia are now at least 30 percent more likely to occur due to anthropogenic climate change (Van Oldenborgh et al., 2020). The main reason for this is the increase in global temperatures. At the start of 2019, Australia experienced its hottest summer on record in terms of both seasonal mean and mean maximum temperatures. In December 2019, during the peak of the fire event, ‘national mean and mean maximum temperature anomalies were respectively at 3.21 and 4.15 °C above the 1961-90 December average’ (Van Oldenborgh et al., 2020). Such high ‘anomalies’ have become common as in 2018 it was reported that nine of the country’s top ten hottest years had occurred since 2005 (Bureau of Meteorology, 2019) and this is likely to set the precedent for future years. In 2019, Australia was named as the most vulnerable nation to climate change amongst all other developed nations (National Climate Science Advisory Committee, 2019). The report claims that global warming has caused increased frequency and intensity of extreme heat and drought and longer fire seasons. Fig.1., gives a visual representation of this, showing the number of days where mean temperatures in Australia were in the warmest 1% day of each month from 1910 to 2019.

Fig. 1. Graph taken from ‘State of the Climate 2020’ report showing the number of days where the Australian area-averaged daily mean temperature was extreme (CSIRO & Bureau of Meteorology, 2020).

Extreme Weather Events and Drought

Another way in which global warming has influenced the 2019-20 Australian bushfires is through droughts caused by two modes of tropical variability: the Indian Ocean Dipole and El Niño Southern Oscillation events (Wang & Cai, 2020). The Indian Ocean Dipole (IOD) is a climate phenomenon in which an irregular oscillation of sea surface temperatures causes the western Indian Ocean to become alternately warmer and the colder than the eastern part of the ocean. The warmer phases are known as positive phases and the colder phases are known as negative phases and positive phases (Bureau of Meteorology 2016). During a positive phase, when conditions are warmer in the eastern Indian Ocean, this causes less precipitation and therefore more droughts in Australia. On average, four of these positive-negative events occur during a 30-year period however there have been twelve positive phases since 1980 and only one negative event since 1992 which suggests that there is increased frequency of extreme IOD events due to greenhouse warming (Cai et al., 2014). 

El Niño is a climate pattern that describes the ‘unusual warming of surface waters in the eastern equatorial Pacific Ocean’ (National Geographic, n.d.). In Australia, during years of an El Niño event there are increased average temperatures and less precipitation leading drought and more extreme fire weather (Harris & Lucas, 2019). Whilst the frequency of an El Niño event can be irregular, they generally occur every two to seven years and a period will last between two to twelve months. It has also been found that El Niño events are becoming increasingly more intense due to anthropogenic warming (Wang et al., 2019; Marjani et al., 2019). Both climate phenomena individually contribute to the weather conditions in Southern and Eastern Australia by causing increased drought and higher temperatures. However, in 2018 and 2019 there was a two-year consecutive concurrence of a positive IOD and El Niño. The conjunction of these events has only occurred once since 1911, indicating that this could be one the reasons as to why the 2019-2020 bushfire season in Australia was so severe (Wang & Cai, 2020). Furthermore, the increased frequency of these events due to climate change indicate that fire events as severe as the 2019-2020 season may begin to occur much more frequently. 

Increased Evaporation Rates

Increased temperatures and drought over long periods of time have caused evaporation rates on Australian vegetation to set new records, particularly in eastern states where the 2019-2020 bushfires occurred. In July 2018, national mean evaporation averages were 145.21 mm, which is 16.61 mm above the average July rates, and the highest rates since 1975 (Hannam, 2018). Evaporation rates were highest in 2018 in eastern Australia as shown in Fig. 2.

 

Fig. 2. Graph showing evaporation rates in Eastern Australia from 1975-2018 (Hannam, 2018).

With increased evaporation rates comes dry or even dead vegetation, which burns more easily than vegetation with high levels of moisture (Zhou et al., 2015). As these record evaporation rates occurred one year before the 2019-2020 extreme bushfire event, it is likely that these contributed to the rapid spread of the fires. Since these high evaporation rates are caused by increased global temperatures and low precipitation levels, this is another example as to how climate change has influenced the Australian bushfires. 

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