Was 2020 an exceptional year for fires in the Northern Hemisphere extratropics?

Author: Anton Darmenov

The 2020 wildfire season in the extratropical region of the Northern Hemisphere was marked by extreme fires in Siberia and the Western United States, and uncharacteristically weak fire activity in Alaska and Canada. Comparison with estimates of historical (2003 through 2019) fire emissions indicated that 2020 was an exceptional year in terms of the total amount of pyrogenic carbon released in the atmosphere by wildfires in Siberia and the Western United States.

Description of animation: The NASA/GMAO atmospheric and aerosol assimilation system GEOS uses observations and numerical models to provide detailed view of the Earth’s atmosphere and surface. The image depicts smoke from the 2020 fires in Siberia and the Western United States. Also shown are time progressions of the 2020 and historical (individual years, starting 2003 through 2019) cumulative emissions of CO2 from fires in the two regions.

The wildfires in Siberia released about 300 Mt of carbon dioxide (CO2), or about 225 Mt more than the median value of the CO2 emissions from this region for the previous 17 years. For comparison, in 2019 and 2012, which were the years with the second and third highest fire emissions, about 200 Mt of CO2 were emitted by biomass burning. Time series of the regional fire emissions showed that the 2020 fire season was characterized by continuous and intensive burning with several well-defined episodes. The fire activity largely subsided by the end of September, making this season also exceptionally long — two to four weeks longer than it is typical for this region.

The amount of CO2 released from wildfires in the Western United States in 2020 was the highest on record since 2003. The 2020 fires emitted about 280 Mt-CO2, which is 200 Mt-CO2 more than the median value of total regional emissions for this region. Analysis of the daily and cumulative emissions showed that in June and July the fire activity was following the regional fire climatology, however this behavior changed abruptly in the middle of August when extreme fires caused large spike in the emissions, followed by another episode in September. Compared to the second and third highest ranking 2012 and 2007, the fires in 2020 emitted about 100 Mt-CO2 more which is an increase of over 30%.

slide graphic
Figure 1: Summarized results from the analysis of the CO2 emissions from fires in Siberia (top) and Western US (bottom). Each graph shows the cumulative emissions since June 1 for the year 2020 (solid orange line), the years 2003 through 2019 (solid gray lines), median of the historical emissions (solid black line), as well as time series of the daily regional emissions in 2020 (dashed orange line). The total fire emissions for this period in 2020 from fires in both Siberia and Western US are the highest ranking since 2003 with approximately 300 Mt and 280 Mt of CO2 released in the atmosphere. The fire emission estimates are made using the GMAO’s Quick Fire Emissions Dataset (QFED; Darmenov and da Silva, 2015).

In contrast, the 2020 fire activity in Alaska and Canada was well below the fire climatology. The combined fire emissions of CO2 from these two regions were about 6 Mt. The highest ranking year of fire emissions in Alaska was 2004 with 135 Mt-CO2. The highest-ranking year of fire emissions in Canada was 2014 with 115 Mt-CO2.

The Fire Weather Index (FWI) based on the commonly used formulation from the Canadian Forest Fire Weather System (Van Wagner, provides convenient numerical measure of fire intensity potential. We used MERRA2 to create FWI anomaly map to gain insight into the role of key meteorological parameters, such as temperature, wind, precipitation and humidity, on the 2020 fires. The positive FWI anomalies in Siberia and Western US are collocated with the locations of the observed fires. The strong relationship between negative departures from the FWI climatology and reduced potential for fires is also evident in Canada and Alaska. Thus, we can partially attribute the behavior of the fires in the major burning regions in the Northern Hemisphere extratropics to the persistent weather patterns during the 2020 fire season, e.g., a historic high latitude heat wave in Siberia.

slide graphic
Figure 2: Map of Fire Weather Index (FWI) seasonal anomalies (2020 minus the mean of 2003-2019 for the period June through September). Higher positive anomalies are indicative of increased potential of wildfires, whereas lower negative anomalies point to reduced fire potential. Positive FWI anomalies are present in the Siberia and Western US regions. The meteorological parameters integrated into the FWI suggest reduced potential for wildfires in Canada and Alaska.


Darmenov, A. S., A. da Silva, 2015: The Quick Fire Emissions Dataset (QFED): documentation of versions 2.1, 2.2 and 2.4. NASA Technical Report Series on Global Modeling and Data Assimilation 38 (NASA/TM–2015–104606), R.D. Koster (Ed.), p. 212.

Van Wagner, C. E.: Development and Structure of the Canadian Forest Fire Weather Index System, Technical Report 35, Canadian Forestry Service, Ottawa, ON, 1987.

« GMAO Science Snapshots