It concerns more than 700 billion kilograms of CO2 that was pumped into the air during the devastating forest fires; nearly double Australia’s annual fossil emissions.

Images of the devastating bushfires that raged in Australia during the summer of 2019 and 2020 are clear. Dark, menacing plumes of smoke tower over the once green forests. Millions of hectares of nature reserve went up in flames during the fierce forest fires. In a new study, Dutch researchers have used satellite data to calculate exactly how much CO2 is released. And these are immense numbers.

Eucalyptus forests

As has often been stated, wildfires in Australia are not uncommon; it is an annual phenomenon. There are particularly frequent fires in the savanna landscape. But what made the ‘Black Summer’ fires so unique was that they mainly raged in eucalyptus forests, where we don’t really see such large fires very often. And that has also had an influence on the amount of CO2 emitted. “Unlike savannas, eucalyptus forests have a much higher density of combustible biomass and thus carbon,” researcher Ivar Van der Velde explains in an interview with Scientias.nl from. “This translates into higher CO2 emissions. In addition, eucalyptus trees contain certain oils that make them extra susceptible to ignition.”

TROPOMIA

However, the question is how much CO2 was pumped into the atmosphere during the devastating forest fires. Earlier models already gave estimates of the emissions, but they showed different variations. Because of this, we didn’t really know how much greenhouse gases and other pollutants were emitted during the fires. The researchers in the new study used satellite data of atmospheric carbon monoxide (CO), collected by the Dutch satellite instrument TROPOMI, for their estimates. This instrument measures not only the emissions of fires, but also the impact on the amount of CO in the atmosphere. Because the ratio between CO and CO2 released during fires in eucalyptus forests is fairly well known, the researchers were also able to trace back the CO2 emissions from the ‘Black Summer’ fires.

The carbon monoxide concentration [mol/m2] measured with TROPOMI over Australia on December 20, 2019. Image: SRON

The Dutch team found that the emissions caused by the forest fires were much higher than originally thought. For example, the total CO2 emissions from the devastating Australian bushfires are estimated at more than 700 billion kilograms. That’s comparable to annual emissions from global air travel and nearly double the annual emissions from fossil fuel consumption across Australia. So it’s a huge amount. “It is alarming that we have seen peaks of very high CO2 emissions in a very short time frame,” says van der Velde. “This is very hard to handle for the natural reservoirs of carbon, such as vegetation and oceans. It is therefore questionable whether our planet has the capacity to compensate for these extreme events in the near future.”

Heap
However, there is reason for hope. Yesterday an article appeared on Scientias.nl in which researchers suggested that the emissions from the Australian bushfires have been partly compensated by gigantic algal blooms in the Pacific Ocean. The smoke from the Australian bushfires contained low but significant concentrations of iron. And that’s vital for the thriving of phytoplankton, which absorb carbon dioxide from the atmosphere during photosynthesis. To what extent exactly this happened during the Australian bushfires is still uncertain.

According to the researcher, it is important that we now have more accurate estimates of the total CO2 emissions from the Australian bushfires. “CO2 is an important greenhouse gas,” says Van der Velde. “And if you look at global CO2 emissions, fires are very relevant. Fires represent about 20 percent of fossil emissions. Until now, however, we assumed that those fires don’t really count, because the emissions are compensated by the absorption of CO2 during regrowth. This does not apply to fires in deforestation areas where vegetation is permanently removed, such as in the Amazon (this represents about 5 percent of fossil emissions). But perhaps ordinary wildfires, such as the ones we’ve seen in Australia, could also become a net source of CO2. To what extent we don’t really know. But vegetation growth is unlikely to return to ‘old’ levels as forest fires become more frequent. This will likely contribute to even more CO2 in the atmosphere than expected.”

Global warming

It means that the fires were so large that we cannot count on a rapid recovery of the damaged forests. As a result, it is likely that some of the emitted CO2 will not be compensated during regrowth. This CO2 then remains in the atmosphere longer and thus contributes to global warming. It does not look like we can turn the tide in the short term. “While it’s still speculative, given current global warming trends, we think we’ll see more such large fires in Australia in the future, and possibly elsewhere,” says Van der Velde. “This will also contribute to even more CO2 in the atmosphere.”

While that may sound daunting, the researchers emphasize that everything we do to reduce our carbon footprint is for good reason. “Our research should not be taken as an excuse that reducing the human-made carbon footprint will not have a significant impact on global CO2 levels and climate change,” says Van der Velde. “The Australian fires did indeed emit a lot of CO2, but we have to remember that these fires were historically abnormal and fortunately will not happen every year. On a global scale, annual man-made CO2 emissions are still five to six times greater than those from wildfires.”