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# The hidden warming effects of the degradation of tropical moist forests

Wei Li, Philippe Ciais

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## To cite this version:

Wei Li, Philippe Ciais. The hidden warming effects of the degradation of tropical moist forests. Nature Geoscience, 2023, 16 (3), pp.200-201. 10.1038/s41561-023-01139-w. hal-04203072

HAL Id: hal-04203072

https://hal.science/hal-04203072v1

Submitted on 4 Oct 2025

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# The hidden warming effects of the degradation of tropical moist forests

Satellite observations show that 24.1% of tropical moist forests are degraded. In addition to the warming effects of the release of carbon from biomass, satellite data suggest that degradation could also increase the land surface temperatures of the affected regions. This biophysical feedback could hinder forest restoration initiatives.

## The question

Forest degradation refers to biomass loss and canopy cover reduction caused by forest fragmentation, fire, selective logging, and unusual weather events. In the Brazilian Amazon, the total area of degraded forest and the resulting carbon emissions are estimated to be larger than those associated with deforestation<fnref n="1" />,<fnref n="2" />. Like deforestation, forest degradation has biogeochemical effects, for example, it releases stored carbon, contributing to global warming. Degradation also has biophysical effects, for example, it alters the local temperature by changing the energy properties of the surface such as the albedo (how much solar energy the surface reflects) and rate of evaporative cooling³. However, the biogeochemical and biophysical effects of tropical forest degradation remain unclear because of the weak contrast between the properties of degraded and non-degraded regions and the lack of high-resolution data. Additionally, the effects of degradation on the local temperature are ignored by previous assessments of the climate impacts of forest disturbances.

## The discovery

We used high-resolution satellite observations of tropical moist forest cover during 1990–2010, above-ground biomass in 2010, burned areas during 2005–2009, and land surface temperature (LST) in 2010. Using these data, we identified four types of degraded forests in the humid tropics (the region between the Tropics of Cancer and Capricorn): burned forest, isolated forest, edge forest, and other degraded forests. We then calculated the biophysical effects of degradation using the difference between the LST of degraded forests and that of adjacent interior forests. We also quantified the above-ground carbon (AGC) deficit: the difference between the mass of carbon stored in degraded forests and adjacent interior forests, which we then converted into an equivalent LST warming effect. Some degraded forests such as isolated and edge forests already existed prior to human involvement; therefore, we separated the forests that were degraded before and after 1990 and estimated the warming effects induced by anthropogenic activities after 1990.

We found that 24.1% of the total forest area was degraded, with the largest contribution from edge forests. The LST of degraded forests is higher than that of adjacent interior forests (Fig. 1a). Averaging the local biophysical warming effects over the total tropical

land area reveals that forest degradation leads to an LST increase of 0.022 ± 0.014 °C in the tropics. The AGC density is 21.8 ± 16.6 tons per hectare lower in degraded forests than in interior forests, with the largest difference in burned forests (Fig. 1b). The total carbon deficit of degraded forests is 6.1 ± 2.0 billion tons of carbon (PgC), which is equivalent to a biogeochemical warming effect of 0.026 ± 0.013 °C. Thus, the biophysical and biogeochemical warming effects of degradation have comparable magnitudes. Approximately one-third of the total area of degraded forest was formed during 1990–2010, which induced a daytime warming effect of 0.018 ± 0.008 °C and a carbon deficit of 2.3 ± 0.8 PgC. The biophysical and biogeochemical effects of forest degradation that occurred in this time period are comparable with the effects of deforestation in the tropics.

## The implications

Our results show that the biophysical and biogeochemical effects of tropical moist forest degradation contribute equally to regional warming. We also found that the contribution of degradation to climate warming is as important as that of deforestation. Our research shows that biophysical warming could impair forest growth and hinder restoration initiatives. Therefore, forest protection programmes to prevent tropical forest loss and degradation are needed to bring biophysical cooling in addition to carbon storage.

Although we used multiple high-resolution satellite datasets to ensure the robustness of our results, some uncertainties remain. For example, the biomass data may not capture biomass gradients in high biomass areas owing to signal saturation⁴. LST data is affected by clouds, especially during the wet season, and no high-resolution night-time LST data is available. Additionally, our method uses measurements of regions at different stages of development as a substitute for measurements at multiple time points owing to the lack of continuous high-resolution satellite data.

With more data, our analysis could be extended to cover temporal changes on a global scale. Incorporating forest degradation into earth system models could help predict changes in the carbon and temperature dynamics of tropical forest ecosystems induced by disturbances.

Wei Li<fnref n="1" /> & Philippe Ciais<fnref n="2" />

**This is a summary of:**

Zhu, L. et al. Comparable biophysical and biogeochemical feedbacks on warming from tropical moist forest degradation. Nat. Geosci. https://doi.org/10.1038/s41561-023-01137-y (2023).

**Publisher's note**

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Published online: 2 March 2023

<footnote n="1">¹Tsinghua University, Beijing, China.</footnote>

<footnote n="2">²Laboratoire des Sciences du Climat et de l'Environnement, Gif-sur-Yvette, France.</footnote>
## EXPERT OPINION

"The authors show that degraded tropical forests are warmer than nearby intact forests through analyses of multiple high-resolution satellite products. This biophysical warming is 0.11°C over the tropics, where degraded forests already contribute to an average warming of 0.08°C through the

carbon emissions. This work is an important step towards understanding the direct and indirect climate benefits of reducing forest degradation through climate mitigation policies." Yue Li, University of California, Irvine, Irvine, USA.

## FIGURE

<figure><img src="image_5.png" /><figcaption>**Fig. 1 | Biophysical and biogeochemical effects of degraded forests.** a, Kernel density distributions of the difference between the LST of each land cover type and that of the corresponding interior forest (ΔLST) for the deforested land and four degraded forest types. b, Kernel density distributions of the</figcaption></figure>

difference between the AGC density of degraded forests and that of the interior forest (AGC density deficit) for the four degraded forest types. The black dashed line indicates zero difference. The coloured dashed lines and the corresponding numbers show the weighted mean values. © 2023, Zhu, L. et al.

## REFERENCES

1. Matricardi, E. A. T. et al. Long-term forest degradation surpasses deforestation in the Brazilian Amazon. *Science* **369**, 1378–1382 (2020).

**This paper reports the area of forest that was degraded in the Brazilian Amazon from 1992 to 2014.**

2. Qin, Y. et al. Carbon loss from forest degradation exceeds that from deforestation in the Brazilian Amazon. *Nat. Clim. Change* **11**, 442–448 (2021).

**This paper uses vegetation optical depth data to calculate the carbon released to the atmosphere owing to forest degradation in the Brazilian Amazon.**

3. Li, Y. et al. Local cooling and warming effects of forests based on satellite observations. *Nat. Commun.* **6**, 6603 (2015).

**This paper reports the biophysical effects of forest and non-forest lands.**

4. Santoro, M. et al. The global forest above-ground biomass pool for 2010 estimated from high-resolution satellite observations. *Earth Syst. Sci. Data* **13**, 3927–3950 (2021).

**A paper that describes the high-resolution global biomass dataset generated from satellite observations of synthetic aperture radar backscatter around 2010.**

5. Zhao, Z. et al. Fire enhances forest degradation within forest edge zones in Africa. *Nat. Geosci.* **14**, 479–483 (2021).

**This paper reports the effects of fires on the carbon deficit in the forest edge zone in Africa.**

## BEHIND THE PAPER

I found out about the biophysical effects of forests from a colleague in 2016 and have had a great interest in them ever since. The biophysical effects of deforestation are well documented by previous studies, and I wondered whether forest degradation has similar effects. Degraded forest is still forest cover and usually occurs on smaller scales than deforestation. Therefore, observing the difference between the temperature signals of degraded and non-degraded forests requires higher-resolution data than

that needed to measure deforestation. As high-resolution LST and biomass satellite data became available and with support from our co-authors, we extended our previous analysis of the effects of fire on edge forests in Africa⁵ to the whole tropics and estimated the biophysical and biogeochemical effects of forest degradation. Despite the challenge of processing such large datasets, we found that the warming effects of degradation are consistent across multiple datasets. L.W.

## FROM THE EDITOR

"Climate impacts of forest disturbance are usually estimated on the basis of biogeochemical changes. Here, the findings of Li et al. show that biophysical effects of tropical rainforest degradation, which reduce evaporative cooling, are just as important to the resulting warming caused by biogeochemical changes. This highlights the urgency to consider biophysical feedbacks when assessing the climate impacts of forest disturbance and restoration strategies." Xujia Jiang, Senior Editor, Nature Geoscience.