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Australia was struck by bushfires in September, and they are still continuing. Is this related to climate change? Delta asked climate scientists from TU Delft and the KNMI.
Smokey clouds from bushfires above the Opera House, Sydney. (Photo: Pxhere)

Australia was struck by bushfires in September, and they are still continuing. Is this related to climate change? Delta asked climate scientists from TU Delft and the KNMI.

Lees in het Nederlands

As early as 2014 the Australian Bureau of Meteorology released a report that higher temperatures caused by climate change would lead to decreases in rainfall and increases in bush fires. Today, in Australia an area of more than two times the size of the Netherlands has already gone up in flames. According to the Dutch newspaper ‘NRC Handelsblad’, the CO2 emissions of the Australian bushfires has already reached 350 million tonnes. This is more than twice the annual CO2 production of the Netherlands.

Professor Herman Russchenberg, climate researcher at TU Delft puts these emissions into context. “To get an understanding of this amount, compare it to the annual worldwide CO2 emission of fossil fuels. This latter is gigatons, and what we now speak of is megatons.”

“CO2 emission is only a bit more than 1% of the annual worldwide CO2 production and is thus not a worrying amount,” says also Jos de Laat, senior researcher at the Royal Netherlands Meteorological Institute (KNMI).

“Besides,” Russchenberg says, “the CO2 released by the bushfires is only temporary as the forest will continue to grow after the fires. And a growing forest consumes CO2. Only, depending on the species of trees, it can take roughly 20 years for a forest to recover from a bushfire. ”

Thunderclouds
According to these climate scientists, the impact of the CO2 emission might be small, the same cannot be said for the weather. Russchenberg says that the local weather is determined by the bushfires. A burning forest needs oxygen. The strong upwards draught of hot air sucks in air from the sides. This causes the wind to rise.

It works like a chimney, the hot smoke ascends and the air that is drawn in from the sides kindles the fire. (Illustration: Sija van den Beukel)
It works like a chimney, the hot smoke ascends and the air that is drawn in from the sides kindles the fire. (Illustration: Sija van den Beukel)

De Laat explains it as follows. “It works like a chimney, the hot smoke ascends and the air that is drawn in from the sides kindles the fire.” Russchenberg continues: “The smoke, ash and dust in the air cause thunderclouds to form.” De Laat adds that “These are not normal clouds as they contain so much particulate matter and dust that too little water is left for condensation and drop formation. These clouds can form thunder though.”

These clouds are so big, that they generate their own weather. If they travel to New Zealand, you would expect the temperature to drop because they block sunlight. De Laat: “For example, in 2017 there was a day that the bushfires in Portugal affected the weather in the Netherlands. It was less sunny that day and the temperature dropped a few degrees because of the clouds from the Portugal bushfires.”

Dust particles reach the stratosphere
De Laat, co-author of several studies on the dissemination of bushfire smoke, including from Australian bushfires, saw that this cloud formation caused particles to rapidly reach great height. “The smoke has now reached the stratosphere at a height of more than 15 kilometres. This is above the atmosphere, where our weather is formed. In the stratosphere, the particles can float around for a long time. There they have a cooling effect on the earth’s surface, because they prevent sunlight from reaching the earth. This same effect happens after strong volcanic eruptions.”

New Zealand glaciers covered in ashes
Dust from the bushfires is also transported across the Tasman Sea and end up at New Zealand’s glaciers and snow tops. The snow is now coloured brown, which tends to absorb the sunlight and increase glacier melt. Professor Andrew Mackintosh, Head of the School of Earth, Atmosphere and Environment at Monash University in Melbourne, who has studied glaciers in New Zealand for nearly two decades, said in the Guardian, that he estimated a 20 to 30 percent increase in this season’s glacier melt. 

The impacts of the dust event would likely last no longer than a year, Mackintosh says, but if Australia continued to be impacted by extreme wildfires and droughts “it will be one of the factors that is accelerating the demise of glaciers in New Zealand overall”.

Indian Ocean
One thing De Laat says he missed in the discussion about the  bushfires, is that once in a while the droughts in Australia are more extreme than in other years. “These droughts are strongly related to seawater temperature in the Indian Ocean. The west side of the Indian Ocean is now warmer than average and the east side is cooler than average. This is causing the increased drought in Australia. Such extreme temperature differences in the Indian Ocean happen once every 10 or 20 years. When this occurs, we see that the bushfires in Australia are more extreme than usual.” 

He does not expect bushfires such as these to happen next year again. “However, there are indications that the frequency of this seawater temperature pattern will rise.”

Whether or not forest fires are caused by climate change is hard to tell. However, Russchenberg does see the forest fires as a warning: “The only way to prevent the increasing severity of bushfires in Australia is to prevent temperature rise, thereby reducing CO2 emission, he says.  Australia still has one of the highest carbon emissions per person – twice the European average and comparable to the USA and Canada. The last few governments have had more climate sceptics. “Of course it is not the case that if we reduce CO2 emissions that there will be no bushfires next year. But let the bushfires be a warning to take climate change seriously. Take action, so that in the long term we can head towards a safe situation.

Extinguishing fires

Seawater is regularly used to extinguish fires near the coast. What consequences does this have for the ecology?

This extinguishing method, in which helicopters hang above the sea and suck up seawater with long hoses, is also often used for forest fires in California. “You can do this in real emergencies, but most of the times it means that the vegetation will respond negatively at first. It then needs time to grow optimally again,” says Emeritus Professor of Hydrology Huub Savenije.

“The salt often damages both crops and forests. If the area is well drained - if the terrain slopes for example - the salt water will probably leach out later. But on flatter terrain that salt can remain for a long time.”

But in Australia, saltwater causes much less ecological damage says Savenije. “The eucalyptus trees that grow there are very resistant to salt. They have very deep roots that reach all the way to the groundwater, and the groundwater in Australia is already quite salty.”

A few years ago, Savenije spent six months on sabbatical in Perth, in the west of the country. He fell in love with the eucalyptus trees. "I have become attached to the smell of eucalyptus oil. It‘s this oil that makes forest fires so fierce in Australia. The oil is highly flammable and is also in the bark. The soil is dotted with eucalyptus oil. Without fire, the trees can’t thrive. Seeds will only germinate after a fire has raged through.”

In Africa however, eucalyptus trees are a disaster. “They are planted because they grow fast and produce good quality wood. But they exhaust streams as their deep roots deplete groundwater reservoirs. In Africa, I hate these trees, but in Australia I love them.” (Tomas van Dijk)

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