Humans, forest fires and climate change

#CarbonCatchers series

Although forest fires are a natural phenomenon, a large number of forest fires are started as a result of human carelessness or deliberately as a business strategy. It is estimated that a staggering 84% of wildfires are in fact caused by humans. Furthermore, #climate change, which is widely demonstrated to be driven by human activities, is increasing both the intensity, frequency and duration of these forest fires. This article is the second in a series of three exploring the topic of forest fires. This article will move on from the first, which explored the change in forest fire patterns throughout geological history, and will investigate the interactions between humans, forest fires and climate change.

The history of humans and fire

The history of humans is interwoven with the ability to use fire. Indeed, it is believed that the rise of Homo erectus, a primitive form of modern humans, was driven by the ability to use fire to cook food and thus increased their overall fitness (Wrangham et al., 1999). Fire also allowed humans to colonise colder environments by keeping them warm, thus promoting the #radiation of humans out of Africa where they first originated 2.5 million years ago (James, 1989). This spread of humans in conjunction with changes in the climate results in the mass disappearance of megafauna such as Mammoths and giant ground sloths (Burney and Flannery, 2005). Humans altered the natural landscape with fire during the Neolithic agricultural revolution in order to clear land for crops, a practice that continues today (Pyne, 1995). Humans so greatly altered the landscape that there is great debate over whether major changes to vegetation in the last 6000 years were caused by climatic changes or were human induced. Such vegetation changes include changes from an area dominated by forest to one dominated by grasses (Olofsson and Hickler, 2008).

Humans changed the land and then the land changed humans. By about 9500 BC, the invention of agriculture led to #sedentarism and stirred the establishment of large civilisations, a radical shift from previous nomadic life. From an estimated 5 million individuals in 10,000 BC, the global population grew to 40 million by 5000 BC and 100 million by 1600 BC. Continuous population growth exacerbated the pattern of land transformation. It is understood that forest fires were the main instrument to such transformation.

The frequency of forest and wildfires has certainly been increasing in recent decades. In the summer of 2019, wildfires in the Arctic circle from Siberia to Canada blazed for an unprecedented 3 months, destroying thousands of hectares of boreal forest and releasing nearly 150 million tonnes of CO2 which produced a smoke cloud larger than the size of the European Union (Watts, 2019). Annual forest fires in Indonesia have been increasing both in intensity and devastation. In 2015 in Indonesia there were incredibly damaging forest fires. These fires occur annually, but the extent of the fires was exacerbated by El Niño, burning 2.6 million hectares of land, the worst fire season in 20 years. Nearly all of these fires were set by humans to clear land for agriculture, mostly palm and rubber plantations, as well as logging, mining and for livestock (Chamorro et al., 2017). This type of agricultural practice, known as #slash-and-burn is also widespread in the amazon rainforest where forest fires in 2019 exceeded 75,000. This led to an estimated burning of 1.8 million hectares of the amazon (Borunda, 2019). Between 2015 and 2017, deforestation in #tropical countries averaged 4.8 billion tonnes of CO2 per year, equating to ~10% of global greenhouse gas emissions (Gibbs et al., 2018). The reasons for such widespread destructive deforestation are usually to create more space for agriculture and livestock farming. With an increasing human population, there is increased demand on food supply chains and other resources.

Figure 1: Smoke cloud above Arctic during 2019 forest fires. Image taken from The Times.

The link between forests and climate change

Forests, such as the Amazon rainforest, act as regulatory systems for both regional and global climate. Forests regulate the local climate by absorbing CO2 as well as other greenhouse gases, resulting in a cooling effect. Thus, the felling of forests and deforestation disrupts this regulatory system and exacerbates the effects of climate change (Peng et al., 2020). In terms of forest fires, it brings about a positive feedback loop where the destruction of forests increases atmospheric CO2, resulting in increased air temperatures, drying out forests and increasing the frequency of forest fires (WWF, 2020). Furthermore, the roots of trees bind the soil and prevent erosions. The loss of this binding affect can leave areas vulnerable to flash #flooding and #erosion.

Climate change has already resulted in increasing average surface temperatures by 0.8°C and looks set to further increase global surface temperatures by 1.5°C, if not much more (Quick et al., 2016). With these increasing temperatures, more regions will experience extreme #drought conditions, less rainfall and subsequently amplification of forest fire intensity and duration (Joyce et al., 2014). For example, in the United states, man-made wildfires have extended the fire season by 108 days. A 2016 study also demonstrated how climate change has doubled the forest fire area since 1984 (Abatzoglou and Williams, 2016). A further example of the link between climate change and forest fires can be seen in Italy. In 2017, Northern Italy experienced one of its driest summers on record with the region experiencing almost no rainfall. Devastating wildfires then in October spread across the Northern alps in the Po valley. 62km2 of forest were lost in the wildfires making it the worst wildfire season in Piemonte for the last 50 years. These events show how climate change can exacerbate forest fires through enhancing drought conditions (Bo et al., 2020).

Impacts of forest fires

Immediately after a wildfire, one of the most obvious impacts is stormwater runoff. Due to the loss of vegetation, soil chemistry is altered leaving soils unable to absorb water. This means that larger volumes of water will flow over the soils, rather than being absorbed by them. This allows for the transportation of debris into larger water bodies. Moreover, flash floods are a major threat after wildfires. These are also caused by the alteration of the soil’s chemistry from the blaze, which allows more water to flow over the soils. There are also heavy metals present in the ash caused by the fire that will flow downstream into larger water bodies, causing significant pollution (Nelson, 2019).

Emissions from forest fires expel into the atmosphere #particulate matter, carbon monoxide, atmospheric mercury, volatile organic compounds, methane, nitrogen oxides as well as CO2 (Crutzen and Andreae, 1990). The release of these compounds can contribute to both the greenhouse effect as well as reducing air quality and can cause respiratory problems in local populations. Furthermore, smoke pollution is a significant health issue (Miranda et al., 2008). Referring back to the Italian wildfires of 2017, there were significant negative impacts on air quality with particulate matter (PM) concentrations in 2017 far exceeding those of previous years at the same time (see figure 2; Bo et al., 2020).

Figure 2: Comparison of particulate matter (PM, proxy for air pollution) concentrations in 2017 (blue line) following Northern Italian bushfires and the average for the years 2005-2016 (orange line). The peak in the blue line (2017) is associated with the Po Valley bushfires, expelling debris and particulate matter into the atmosphere. Graph taken from Bo et al., 2020.

Forest fires and endangered species

Many species of plant and animal are also under increasing pressure as a result of forest fires. A very poignant example is the #Koala in Australia. Prior to the recent bushfires, Koala’s were listed by the IUCN as vulnerable and there were estimated to be between 100,000 and 500,000 individuals left in the wild. As a result of the bush fires, Australia’s environment minister said, the population of Koalas in New South Wales has declined by up to 30% (Zhou, 2019). For a species already in difficulty, this could be the beginning of the end for the Koala. In the Amazon Rainforest, a similar story is told. The WWF (World Wildlife Fund) has said that the 2019 forest fires increased the threats and risks faced by 265 endangered species of plant and animals including the giant anteater and giant armadillo (Chiorando, 2019). The Orangutan in Indonesia is also critically endangered as a result of major habitat loss cleared through slash-and-burn techniques for palm oil plantations, logging and mining (WWF, 2020).

Figure 3: Koala and firefighter in the middle of the New South Wales 2019 bushfires, Australia. Image from Eden Hills Fire Service.

Conclusion

There is a clear link between humans, forest fires and climate change. The deliberate setting of forest fires by humans to clear forest results in increased CO2 emissions, while also reducing the amount of CO2 absorbed by the forests, thus increasing the effects of climate change. At the same time, human induced climate change and the increased temperatures caused by it result in prolonged #drought conditions. These drought conditions exacerbate forest fires. So, there is a positive feedback loop. The way to break this loop is to regenerate forests and halt deforestation, but this will be discussed in more detail in the next article. In the meantime, if you want to contribute to any reforestation projects, you can visit our planting page.

Trends

• If the trend of tropical deforestation continues (mainly as a result of slash-and-burn agricultural practices), it is extremely unlikely that global climate warming will be kept below 2°C.
• The trend in deforestation in tropical areas (such as Indonesia and the Amazon rainforest) has increased in the last decade and is predicted to continue to increase as more land is cleared for primarily agricultural use.
• The occurrence of forest fires is predicted to increase with climate change, which will in turn exacerbate climate change in a positive feedback loop.
• Fires create an excuse for farmers to change the use of the land to farming, greatly reducing the biodiversity and increasing CO2 and methane emissions.

Calculations

• Forest fires in 2019 directly enhanced the risks faced by at least 265 species already threatened with extinction. Although the real figure may be 2 to 3 orders of magnitude higher. A UN report stated that roughly 1 million species are threatened with extinction as a result of climate change, where deforestation is a primary driving factor.
• 370,000 km2 of forest burned in 2019 as a result of forest fires.
• Deforestation, often caused by forest fires, can increase local air temperatures by 1°C.

Keywords: #Fire #ForestFires #ClimateChange #logging #deforestation #plantingtrees #endangeredspecies #EcoEducation

References:

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