Global warming in the Arctic increases megafires on the permafrost
IMAGE: A 30-KILOMETER-WIDE WILDFIRE FRONT DETECTED IN THE SIBERIAN ARCTIC AT A LATITUDE OF 69.31°N ON AUGUST 6, 2020. SENTINEL-2 INFRARED COLOR IMAGE view more
CREDIT: ADRIÀ DESCALS
The Siberian Arctic experienced an unusual number of fires in 2019 and 2020. This raised concerns in the scientific community, as the Arctic has large areas of permafrost, a permanently frozen layer of subsoil that accumulates large amounts of carbon. Fires damage the permafrost and contribute to the release of carbon emissions in the form of greenhouse gases.
The question that remained unanswered was whether this increase in fires in 2019-2020 was an exceptional case or a trend that will get worse as the Arctic warms.
Now, a new study published in Science and led by Adrià Descals and Josep Peñuelas, both scientists from the Spanish Council for Scientific Research (CSIC) and from CREAF, shows that the increase in temperature is driving an exponential increase in fires in the Arctic. David Gaveau, fire expert at TheTreeMap, as well as researchers from the Desertification Research Centre (CSIC-University of Valencia), Wageningen University (Netherlands), the University of Kyoto, and the Center for International Forestry Research (CIFOR) in Indonesia, also participated in the study.
"In 2020 alone," explains Adrià Descals, first author, "423 fires were detected in the Siberian Arctic, which burned around 3 million hectares (an area almost as big as the whole Belgium) and caused the emission of 256 million tonnes of CO2 equivalent", which is similar to the annual emissions of CO2 in Spain. The researcher adds that "with future warming, these megafires will be recurrent at the end of the century and will have different implications, both for the Arctic and for the global climate".
Analysis of four decades of satellite observations
The authors quantified, from satellite observations from 1982 to 2020, the area burned in Siberia above the Arctic Circle, a region covering 286 million hectares. "While the observations indicated that the 2020 fire season was exceptional, no precise quantitative assessment had been made so far in this remote region," says co-author David Gaveau.
In this work, the scientists show that fire risk factors associated with temperature have increased in recent decades and that there is an exponential relationship between the extent burned annually and these factors. "Temperatures are reaching a critical threshold where small increases above the summer average of 10 °C can exponentially increase the area burned and the associated emissions," explains Josep Peñuelas.
The summer of 2020 was the warmest in four decades, and the large area burned between 2019 and 2020 was unprecedented, the authors explain. Approximately 4.7 million hectares burned between 2019 and 2020, resulting in total emissions of 412.7 million tonnes of CO2 equivalent.
"We detected fires above the 72nd parallel north, more than 600 km north of the Arctic Circle, where fires are unusual and where winter ice was still visible at the time of burning," explains Adrià Descals. "Many fires were detected with a few days of difference, so we hypothesise that increases in thunderstorms and lightning are the main cause of the fires, although further investigations would be required to demonstrate how much human activities may influence the fire season in this remote region."
Rising air temperature and fire risk
Some factors that can exacerbate fire risk have increased significantly, and all these factors are related to rising temperatures. The study explains that factors such as drier weather conditions, longer summers, and more vegetation have shown a consistent trend over the past four decades.
The authors note that "the 2020 average summer temperature - which was 11.35 degrees - will be very common from the second half of the century on if the Arctic warming continues at the same rate." As Adrià Descals warns, "these temperature anomalies increase fire risk factors, so the conditions that were led to the 2019 and 2020 fires will be recurrent in the Arctic by the end of the century."
An explanatory model that links the factors of fire
In 2019 and 2020, fire rates in the Siberian Arctic exceeded those of the last four decades. Only in 2020, there were seven times more fires than the average since 1982 and they damaged an unprecedented area of peatlands. Josep Peñuelas explains that "the concatenation of these factors is what generated the fire rate increase".
"Higher temperatures explain the earlier thaw, which in turn allows for greater vegetation growth and increases fuel availability".
"The fact that there is more and earlier vegetation reduces the availability of water in the soil, and plants suffer greater water stress," says Aleixandre Verger, a researcher at CSIC and CREAF.
In turn, "extreme heat waves, such as in 2020 in the Siberian Arctic, increase vulnerability to drought, as they can desiccate plants and reduce peat moisture, and therefore increase the intensity of fires and carbon emissions".
On the other hand, heatwaves and, above all, the increase in surface temperature, can increase convective storms and lightning, which have been very rare so far in the Arctic, but "they are expected to increase as the climate warms", say the scientists.
"Climate warming therefore has a double effect on fire risk: it increases the susceptibility of vegetation and peatlands to fire and, on the other hand, it increases the number of ignitions caused by thunderstorms," explains Adrià Descals.
Our work suggests that the Arctic is already experiencing a change in fire regimes caused by climate warming. "The areas burned in 2019 and 2020 could be exceptional events, but recent temperature trends and projected scenarios indicate that, by the end of the century, large fires such as those in 2019 and 2020 will be frequent if temperatures continue to increase at the current rate," conclude Adrià Descals and Josep Peñuelas.
JOURNAL
Science
Arctic warming linked to increasing Arctic wildfires
Continued global warming is creating conditions that will likely cause dramatic increases in Arctic wildfires within the coming decades, potentially releasing massive stores of organic carbon from burned peatlands into the atmosphere, according to a new study. Using satellite data, Adrià Descals and colleagues show that the fires in the Siberian Arctic burned nearly 4.7 million hectares (Mha) in 2019 and 2020, which accounted for 44% of the total burned area in this region for almost the last 40 years. They argue that temperatures in the Arctic – one of the most rapidly warming regions on the planet – could be headed towards a threshold where small temperature increases could result in exponential increases in area burned. Arctic soils store vast amounts of organic carbon, much of which is in the form of peatlands. Although often frozen or waterlogged, climate warming thaws and dries peatland soils, increasing the likelihood of large Arctic wildfires. Burning of these carbon-rich soils releases this carbon into the atmosphere as carbon dioxide, fueling a feedback loop of continued warming, subsequent burning, and CO2 emission. Descals et al. used six satellite-derived maps to evaluate annual burned area in the Siberian Arctic for 1982-2020 and combined it with an analysis of 10 climatic factors associated with the likelihood of fires, including temperature and precipitation. They found that fires burned at the highest rates in 2019 and 2020 and accounted for 44% of all the total area burned across their nearly 40-year-long study period, releasing almost 150 million tons of carbon into the atmosphere. 2019 and 2020 were also the warmest years across the study. According to the authors, the findings suggest an exponential relationship between fire associated with increased temperature and annual burned area. The Siberian Arctic has already doubled the long-term average of burned area in just the last three years of their analysis. This could indicate a profound shift in the region’s fire regimes caused by accelerating climatic warming. “Larger and more intense wildfires could substantially accelerate the release of permafrost carbon into the atmosphere, but this interaction is not considered in current forecasts of Arctic feedback to global warming,” write Eric Post and Michelle Mack in a related Perspective. “Future studies that link rigorous assessment of wildfires with the dynamics of permafrost thaw in these remote regions are therefore needed to better quantify their climate impact.”
For reporters interested in trends, another study in this issue also investigates recent extreme Siberian wildfire seasons. In this study, Rebecca Scholten and colleagues used data from the satellite-borne Moderate Resolution Imaging Spectroradiometer (MODIS) to evaluate fire activity in the Siberian Arctic between 2001 and 2021. Scholten et al. found that early snowmelt combined with an anomalous Arctic front jet over northeastern Siberia promoted unusually dry and warm surface conditions, which was followed by unusually high lightning and fire activity. They show that these interconnected climatic drivers have been increasing over the last several decades and are likely driving extreme fire activity in the region. These fires have the potential to accelerate the thawing and degradation of carbon-rich permafrost peatlands.
JOURNAL
Science
ARTICLE TITLE
Unprecedented fire activity above the Arctic Circle linked to rising temperatures
ARTICLE PUBLICATION DATE
4-Nov-2022
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