An international research team, led by the French Alternative Energies and Atomic Energy Commission (CEA) and INRAE, has unveiled the first comprehensive mapping of annual changes in global forest biomass from 2010 to 2019 using a new satellite image analysis method. Their findings, published in Nature Geoscience, challenge existing models and reveal critical insights for climate change mitigation strategies.
The study highlights the pivotal role of increased plant biomass in carbon sequestration, a vital component in mitigating climate change. Changes in forest carbon stocks result from a delicate balance between gains, such as plant growth and forest expansion, and losses, including deforestation, degradation, and natural disturbances. Understanding and monitoring these changes are essential for effective climate change mitigation policies.
The researchers harnessed vegetation data from the Soil Moisture and Ocean Salinity (SMOS) satellite, utilizing L-band vegetation optical depth (L-VOD) methods. This unique approach allowed them to estimate average above-ground carbon stocks globally. However, L-VOD has limitations, including signal interference from human activities and sensitivity to vegetative water content.
To overcome these challenges, the team developed a double filter incorporating temporal signal decomposition. They then calculated the spatial and temporal distribution of total live biomass carbon in terrestrial ecosystems from 2010 to 2019. This information enabled them to create maps of annual biomass carbon changes, assess regional carbon budgets, and attribute carbon losses and gains to factors such as fires and land-use changes. Furthermore, they explored how forest age impacts terrestrial carbon storage.
The study’s key findings are as follows:
Global Increase in Carbon Stocks: Over the ten-year period, terrestrial biomass carbon stocks increased by approximately 500 million metric tons of carbon per year.
Boreal and Temperate Forests Lead Carbon Sinks: Boreal and temperate forests emerged as the primary global carbon sinks due to their young to middle-aged tree populations.
Tropical Forests Nearly Carbon Neutral: Tropical forests, especially old-growth ones with trees over 140 years old, are nearly carbon neutral. Deforestation and tree mortality following droughts have shifted them from carbon sinks to small carbon sources.
These findings challenge previous predictive models that labeled all old-growth forests as significant carbon sinks. The study underscores the need to account for forest degradation, forest age, and the impact of deforestation and degradation on tropical forests when predicting global carbon sink dynamics. Such considerations are crucial for crafting effective climate change mitigation policies.
In summary, this groundbreaking research enhances our understanding of global forest biomass changes and their implications for climate change mitigation. It emphasizes the importance of incorporating forest degradation and forest age into predictive models to develop tailored climate change policies.