Forest Fires: Sink or Source

A look into Forests’ role in Carbon Sequestration

Published in

EARTH by map-collective.com

7 min readSep 25, 2020

2019 and 2020 fire seasons have been record-breaking worldwide: the Amazon, Arctic, Australia, and the United States. We’ve transitioned into a hot new world, but what does that mean for our forests? Are they burning too much? How absurd is this?

Forests are responsible for 25% of all planned emissions by 2030 under the Paris Agreement (1). When we read headlines that wildfires are burning at an unprecedented rate, what should the public think?

Forests are a natural carbon sink

Forest fires are a natural part of forests. They promote seedling growth and discourage non-native species growth. Native Americans knew this importance and had been managing forests with fires for centuries. This cultural burning has been lost, as fire suppression keeps a growing population and their property out of harm’s way. With more leaf fuel on the ground, higher annual temperatures, increased droughts, forest fires have become much harsher.

Historically the growth of forest biomass outweighs the number of emissions from fires. Now, we see more fires that are more intense at a time where forests are more stressed due to increased temperatures. Simultaneously, the conservation of forests has been a continuous, losing battle.

Forests play a vital role in the Earth’s carbon cycle. Research states that nearly land-based sinks remove 29% of anthropogenic emissions (including land-use change) with a significant contribution from forests (2). In Drawdown, the most comprehensive plan ever to reverse the effects of global warming claim that tropical forests are our fifth best solution, and temperature forests are our 12th best solution with the capability of removing 80 Gigatons of carbon combined by 2020. This is huge, considering that it is a free ecosystem service, and it only takes conservation enforcement and acceptable policy. Currently, temperate and tropical forests combine to remove roughly 13% or 4.7 Gigatons of anthropogenic carbon dioxide emissions a year.

Smoke signals forests are transitioning into a carbon source

When discussing emissions from forest fires there are two key aspects to this dialogue.

1. Not all forests are the same.
2. Intentional fires and unintentional fires are two very different stories with vastly different scales of disaster.

When we think of forests, there are typically four main types of forests. There’s tropical rainforests, sub-tropical rainforests, temperate and boreal forests. These clarifications correlate with the water availability and temperature of the equator, above and below the equator and the arctic. As you move away from the equator, the potential amount of carbon sequestration decreases. This is because it takes much more time for trees to grow in harsh climates.

There is an important distinction between types of forest fires. 26% of all forest fires occur naturally, typically by lightning strikes or lava. The rest are either intentional or unintentional fires. Unintentional fires could range from anything such as a gender reveal party gone wrong, escaped campfires, or even flat tires sparking a flame in dry conditions on a forest road. Intentional fires are almost exclusively clearing forest lands for agriculture using fire. This is especially prevalent in developing countries where economic opportunities are minimal.

From 1st January to 31st August 2020, the estimated CO2 emissions for the Arctic region were 244 megatons, compared to 181 megatons for the whole of 2019 (3). To put that in perspective, Spain, the 24th biggest carbon polluter released 244 megatons of carbon dioxide in 2018.

This year’s fires in California, Oregon, and Washington totaled about 60 megatons (4), approximately 1.1% of the United States’ carbon footprint. The 21st century average for the US for forest fire emissions is about 24 megatons a year. The fires in the developed nations or unpopulated areas such as the arctic are almost always unintentional.

In contrast, intentional and unintentional fires combined in the tropics released 6 gigatons or 6000 megatons of CO2e in 2016; therefore, becoming the third biggest polluter after China and the United States classified as a country (5). These emissions don’t even reflect the Amazon rainforests’ worst year yet, which occurred in 2019. 2020 is estimated to be larger by 52% than last year, making 2020 possibly even worse (6).

There is a silver lining to the current forest burning. Modeling ecosystems is incredibly complex. Recent studies have shown that there has been a mistake in modeling these emissions from forest fires. There is an assumption that all of the above biomass is obliterated when a fire occurs, is simply untrue. A study shows that CO2 estimates were combustion are 59%–83% higher than emissions based on field observations (7). In support of this finding, a separate study found that not all carbon is from a fire is released into the atmosphere. 12% of the carbon is sequestered on-site for 1000s of years as solidified pyrogenic carbon (8). The carbon emissions mentioned above likely overestimate the actual value of CO2e emitted.

With our models being inaccurate or possibly misleading, the number of hectares and current carbon emissions are directly correlated. We are seeing a spike in emissions, especially in the past few years. This trend has illustrated that forests around the globe are experiencing feedback loops.

Global warming and Forest Feedback loops

As temperatures rise across the globe, trees are at a higher risk. Below are two figures that explain these feedback loops.

Source: Forest disturbances under climate change (2017) Seidl et al.

When forests begin to burn more frequently, and harsher from these direct and indirect effects and more frequent, the most critical question is, have we reached a tipping point with our forests? Put into other words, will emissions from fires outweigh the carbon drawdown from forests every year, thus transitioning forests into sources rather than sinks?

Burned forests will regrow and begin storing carbon once again. However, these forests are smaller, younger, and drier than before, and, in some ecosystems, their carbon storage capacity is reduced. This results in a net increase in carbon emissions. Depending on species and growth speed, vegetation needs between 25- 250 years to reach its full sequestration potential.(9)

Lastly, as we march into higher temperatures, forests that have not been burned have a variety of responses. Some forests will suffer from stunted growth and tree mortality due to climate change’s direct and indirect effects. Simultaneously, increased temperatures can aid the growth season of temperate and boreal forests, thus increasing carbon drawdown.

Conclusion

It is evident that 2020 has ushered in this climate feedback and it is now taking place. Several studies have looked into this issue. The conclusion is that climate change decreases the potential for the sink to deepen, with and without the disturbance regime.

The severity of forest fires is extremely concerning, especially since we are planning on their existence to drawdown carbon and reduce the impacts of climate change. Without proper management and increased efforts to conserve the current forests and reforestation efforts, we can see global forests becoming a sink rather than a source. Too often, we take for granted the role of global forests. It is a passive mitigation effort and needs to be actively invested in, managed, and protected.

Written by Brendan Hellebusch for Map-Collective.com

References

(1) Grassi, G., House, J., Dentener, F. et al. The key role of forests in meeting climate targets requires science for credible mitigation. Nature Clim Change 7, 220–226 (2017). https://doi.org/10.1038/nclimate3227 https://www.nature.com/articles/nclimate3227

(2) Le Quéré, Corinne, et al. “Global carbon budget 2018.” Earth System Science Data 10.4 (2018): 2141–2194.

(3) Worst-Ever Arctic Fires Released Record Amount of CO2 https://www.bloomberg.com/news/articles/2020-09-03/climate-change-arctic-fires-in-2020-released-record-carbon

(4) 6 Graphics Explain the Climate Feedback Loop Fueling US Fires https://www.wri.org/blog/2020/us-fires-climate-emissions

(5) By the Numbers: The Value of Tropical Forests in the Climate Change Equation

https://blog.globalforestwatch.org/climate/by-the-numbers-the-value-of-tropical-forests-in-the-climate-change-equation/?utm_campaign=BLOG:+Climate+Change+Explainer&utm_medium=bitly&utm_source=GFWBlog

(6) Global fires are up 13% from 2019’s record-breaking numbers https://www.independent.co.uk/environment/climate-crisis-fires-global-heating-amazon-california-eu-a9690146.html

(7) Fixing a snag in carbon emissions estimates from wildfiresFixing a snag in carbon emissions estimates from wildfires, Stenzel et al. (2019) https://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.14716

(8) Global fire emissions buffered by the production of pyrogenic carbon Matthew W.J. et al. (2019) https://www.nature.com/articles/s41561-019-0403-x2019

(9) Fires, Forests and the Future:A Crisis Raging out of Control? (2020) WWF and BCG https://wwfeu.awsassets.panda.org/downloads/wwf_fires_forests_and_the_future_report.pdf