The overall contribution of tropical forests to the global carbon footprint is surprisingly just about neutral. The science has not changed: trees, and therefore forests, do act as essential sinks that suck up excess carbon from the environment; however, the impact of deforestation and forest degradation has mitigated all the good done by nature to prevent or at least minimize global warming.
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Tropical forests are projected to become a source of carbon rather than a sink in the not-so-distant future due to the unrelenting loss of forests and the influence of climate change on the capability of existing forests to collect extra carbon dioxide from the atmosphere. This is an ominous sign for the global effort to keep global warming in check and may fail to limit global warming with the target of 2oC.
Recent international accords have focused on ending deforestation and forest degradation, but one of the major concerns in the effectiveness of these accords was a lack of consistent data to monitor emissions and design models, which made it a challenge to act on defined policies.
Thanks to recent advances in spaceborne technology, high-resolution imaging, and increased processing power, scientists have now got their hands on a revolutionary and potent instrument. In forest surveillance, the importance of accurate data cannot be overstated, and the recent technological breakthroughs have inaugurated what many have dubbed as the golden era of forest monitoring by providing scientists with groundbreaking data on the actual amounts of carbon emission and absorption.
According to experts, it is not only the first step towards developing a worldwide standard for measuring emissions and amount of forest carbon, but it may also bring enormous disparities between the actual amount of carbon stored in a country's forests and the amount claimed to be stored.
The Age of LiDAR
Until recently, forest remote sensing relied heavily on Landsat time-series imagery, providing satellite data with a 30-meter resolution. This data laid the foundations for programs such as the Global Forest Watch (GFW), which delivers forest loss data on a global scale.
For differentiating between surfaces like deserts, forests, and meadows, this data proved sufficient; however, it failed to identify the height of individual trees or a group of trees, which is essential for accurately predicting emissions from a forest. As a result, scientists settled for a crude approximation for this information, relying primarily on ground samples.
Now, however, LiDAR technologies are revolutionizing the entire field of Earth monitoring. Short for Light Detection and Ranging, LiDAR sends lasers down towards the surface of Earth and calculates the distance between the sensor and the Earth's surface to build a 3D representation of the land.
Csillik et al. (2020) used forest carbon estimations obtained from their LiDAR aircraft data, Planet Dove satellite images, combined with other auxiliary information to create machine learning models, which were then used to quantify the entirety of aboveground carbon that was present in Peru.
It was evident from their preliminary findings that it was conceivable to estimate the aboveground carbon accurately in an area using modern technology and computing power. Another interesting discovery was that the study revealed the carbon emissions in Peru directly resulting from deforestation to be about 23% larger than what had been previously estimated using outdated methods.
Previously, LiDAR sensors were mounted on aircraft, and the calculations were performed during flight, a process that necessitated the allocation of large amounts of monetary resources and time. The area that could be studied using the setup was also restricted due to aircraft use.
Now, technological advancements have allowed for the use of LiDAR on the Global Ecosystem Dynamics Investigation mission (GEDI) of NASA, the ICE-SAT-2, and on other such spacecraft. Every year, new satellites are deployed, many of which are specifically designed to detect forest carbon footprints and plant life, ensuring global availability of this formerly expensive and area restricted data. This very transition from aircraft to spacecraft as LiDAR carriers has truly ushered in the golden era of earth observation systems.
A couple of years ago, scientists were able to finally record global carbon emissions, absorptions, and fluxes using this technology, which highlights the pace with which these advancements are being ramped up.
What the Future Looks Like
The question of whether spaceborne LiDAR carriers can be used to monitor forest carbon is not purely technological. Many experts feel that the mainstream implementation of these technologies for properly assessing global forest carbon levels and carbon emissions will be slowed down by politics rather than science.
Scaling these technologies to the national stage could potentially alter the course of a nation and even help establish how much the reliance on trees is worth.
Interview: Continuing NASA's Earth Observation Legacy with Landsat 9
Reference and Further Reading
Csillik, O., & Asner, G. P. (2020) Near-real time aboveground carbon emissions in Peru. Plos One. Available at: https://doi.org/10.1371/journal.pone.0241418
D'Angelo, H. (2019) New satellite system can map tropical forest carbon emissions. Arizona State University News. [online] Available at: https://news.asu.edu/20191202-first-operational-mapping-system-high-resolution-tropical-forest-carbon-emissions-created
Mitchard, E. T. (2018) The tropical forest carbon cycle and climate change. Nature, 559, 527-534. Available at: https://doi.org/10.1038/s41586-018-0300-2
Sax, S. (2019) Missing Forests Are Messing With Climate Targets. Wired. [online] Available at: https://www.wired.co.uk/article/forest-counting-climate-change
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