Edited by Christopher B. Field, Stanford University, Stanford, CA; received October 18, 2025; accepted May 28, 2026
July 6, 2026
123 (28) e2528622123
Significance
Tropical forests are vital for absorbing CO2 and supporting global biodiversity, but rising temperatures threaten their health and functioning. When trees reach critical temperatures, their photosynthetic system breaks down. We mapped the spatio-temporal trends in thermal safety margins (TSM; the gap between canopy temperature and critical thermal threshold) of 208 plant species across tropical forests from 2001 to 2020 using satellite data and species distribution maps. We studied projections of TSMs to 2050 and 2100. Our results indicate declining TSM and increasing extent of areas exceeding critical temperatures, underlining the growing exposure to risks to biodiversity in tropical regions.
Abstract
Understanding how close tropical tree species are to critical temperature thresholds that might impede photosynthetic activity is vital in a world where heat waves have become more severe and frequent. Using remotely sensed surface temperature and species distribution maps, we studied the spatiotemporal variation in the thermal safety margins (TSM, i.e., the difference between Tcrit, the critical photosynthetic temperature, and the maximum canopy temperature) of 208 tropical tree species in South America, Southeast Asia, and Central Africa during the period 2001–2020. Despite overall high-temperature tolerance with an average Tcrit of 46.1°C, we observed a consistent decline in the TSM of tropical forests across the globe. The average pantropical TSM decline was 0.4°C per decade, with the strongest decline in South America (0.5°C per decade). Over the 20-y period, areas that experienced canopy temperatures surpassing the average Tcrit across reported species increased from 43 Mha to 57 Mha in the tropics, representing 4% of the studied area. This number increases to 10% when computing areas where temperatures have surpassed the Tcrit of the most vulnerable reported species. When considering future trends, as predicted by Earth System Models under medium-to-high emission scenarios, average Tcrit may be exceeded in an area of 83 Mha by 2050 and 160 Mha by 2100 (over 10% of the studied area), suggesting major feedback to the global carbon cycle and the world’s biodiversity.
Get full access to this article
Purchase, subscribe, or recommend this article to your librarian.
Data, Materials, and Software Availability
Acknowledgments
N.v.T. and D.T. acknowledge funding from the Swiss NSF SNF through the deepHSM project (200021_204057). G.L. acknowledges funding from the Ecoplains EPFL-ENAC flagship project. M.P.R. acknowledges support from the US NSF Award #2423275, Vetlesen Foundation, and European Union Horizon 2020 Marie Skłodowska-Curie grant #101031748 Terracarb. C.G. was supported by the Swiss NSF SNF (310030_204697 and CRSK-3_220989) and by the Sandoz Family Foundation. We would like to thank Alyssa Kullberg for her careful proofreading and expert advice.
Author contributions
N.v.T., G.L., M.P.R., C.G., and D.T. designed research; N.v.T. and G.L. performed research; N.v.T. and G.L. analyzed data; and N.v.T., G.L., M.P.R., C.G., and D.T. wrote the paper.
Competing interests
The authors declare no competing interest.
Supporting Information
References
1
M. C. Hansen et al., High-resolution global maps of 21st-century forest cover change. Science 342, 850–853 (2013).
2
N. Myers, R. A. Mittermeier, C. G. Mittermeier, G. A. Da Fonseca, J. Kent, Biodiversity hotspots for conservation priorities. Nature 403, 853–858 (2000).
3
S. L. Lewis, D. P. Edwards, D. Galbraith, Increasing human dominance of tropical forests. Science 349, 827–832 (2015).
4
R. Goodman, M. Herold, “Why maintaining tropical forests is essential and urgent for a stable climate” (Working Paper, Center for Global Development, 2014).
5
L. E. Aragão, The rainforest’s water pump. Nature 489, 217–218 (2012).
6
J. C. Jiménez-Muñoz et al., Record-breaking warming and extreme drought in the amazon rainforest during the course of El Niño 2015–2016. Sci. Rep. 6, 33130 (2016).
7
S. J. Wright, H. C. Muller-Landau, J. Schipper, The future of tropical species on a warmer planet. Conserv. Biol. 23, 1418–1426 (2009).
8
J. Berry, O. Bjorkman, Photosynthetic response and adaptation to temperature in higher plants. Annu. Rev. Plant Physiol. 31, 491–543 (1980).
9
K. Hüve, I. Bichele, M. Tobias, Ü. Niinemets, Heat sensitivity of photosynthetic electron transport varies during the day due to changes in sugars and osmotic potential. Plant, Cell Environ. 29, 212–228 (2006).
10
O. S. O’sullivan et al., Thermal limits of leaf metabolism across biomes. Glob. Chang. Biol. 23, 209–223 (2017).
11
K. Feeley et al., The thermal tolerances, distributions, and performances of tropical montane tree species. Front. For. Glob. Chang. 3, 25 (2020).
12
N. Kitudom et al., Thermal safety margins of plant leaves across biomes under a heatwave. Sci. Total. Environ. 806, 150416 (2022).
13
T. M. Perez, K. J. Feeley, Photosynthetic heat tolerances and extreme leaf temperatures. Funct. Ecol. 34, 2236–2245 (2020).
14
T. M. Perez, K. J. Feeley, Weak phylogenetic and climatic signals in plant heat tolerance. J. Biogeogr. 48, 91–100 (2021).
15
N. N. Bison, S. T. Michaletz, Variation in leaf carbon economics, energy balance, and heat tolerance traits highlights differing timescales of adaptation and acclimation. New Phytol. 242, 1919–1931 (2024).
16
M. Slot et al., Leaf heat tolerance of 147 tropical forest species varies with elevation and leaf functional traits, but not with phylogeny. Plant, Cell Environ. 44, 2414–2427 (2021).
17
J. R. Mahan, D. R. Upchurch, Maintenance of constant leaf temperature by plants—I. Hypothesis-limited homeothermy. Environ. Exp. Bot. 28, 351–357 (1988).
18
J. E. Drake et al., No evidence of homeostatic regulation of leaf temperature in eucalyptus parramattensis trees: Integration of CO2 flux and oxygen isotope methodologies. New Phytol. 228, 1511–1523 (2020).
19
C. J. Still et al., No evidence of canopy-scale leaf thermoregulation to cool leaves below air temperature across a range of forest ecosystems. Proc. Natl. Acad. Sci. U.S.A. 119, e2205682119 (2022).
20
A. Gauthey et al., High heat tolerance, evaporative cooling, and stomatal decoupling regulate canopy temperature and their safety margins in three European oak species. Glob. Chang. Biol. 30, e17439 (2024).
21
H. W. Bilger, U. Schreiber, O. Lange, Determination of leaf heat resistance: Comparative investigation of chlorophyll fluorescence changes and tissue necrosis methods. Oecologia 63, 256–262 (1984).
22
R. M. Marchin et al., Extreme heat increases stomatal conductance and drought-induced mortality risk in vulnerable plant species. Glob. Chang. Biol. 28, 1133–1146 (2022).
23
C. J. Still et al., Imaging canopy temperature: Shedding (thermal) light on ecosystem processes. New Phytol. 230, 1746–1753 (2021).
24
C. Justice et al., An overview of MODIS land data processing and product status. Remote. Sens. Environ. 83, 3–15 (2002).
25
Z. Guo et al., Does plant ecosystem thermoregulation occur? An extratropical assessment at different spatial and temporal scales. New Phytol. 238, 1004–1018 (2023).
26
J. B. Fisher et al., NASA’s next generation mission to measure evapotranspiration from the International Space Station. Water Resour. Res. 56, e2019WR026058 (2020).
27
C. E. Doughty et al., Tropical forests are approaching critical temperature thresholds. Nature 621, 105–111 (2023).
28
N. van Tiel et al., Regional uniqueness of tree species composition and response to forest loss and climate change. Nat. Commun. 15, 4375 (2024).
29
H. Hersbach et al., The ERA5 global reanalysis. Q. J. R. Meteorol. Soc. 146, 1999–2049 (2020).
30
M. Puma, B. Cook, Effects of irrigation on global climate during the 20th century. J. Geophys. Res. Atmos. 115, D16120 (2010).
31
D. B. Lobell, S. Di Tommaso, A half-century of climate change in major agricultural regions: Trends, impacts, and surprises. Proc. Natl. Acad. Sci. U.S.A. 122, e2502789122 (2025).
32
V. Eyring et al., Overview of the coupled model intercomparison project phase 6 (CMIP6) experimental design and organization. Geosci. Model. Dev. 9, 1937–1958 (2016).
33
B. Thrasher et al., NASA global daily downscaled projections, CMIP6. Sci. Data 9, 262 (2022).
34
Z. Hausfather, G. P. Peters, Emissions—The ‘business as usual’ story is misleading. Nature 577, 618–620 (2020).
35
L. Liu et al., Increasingly negative tropical water-interannual CO2 growth rate coupling. Nature 618, 755–760 (2023).
36
N. McDowell et al., Drivers and mechanisms of tree mortality in moist tropical forests. New Phytol. 219, 851–869 (2018).
37
W. R. Anderegg, J. M. Kane, L. D. Anderegg, Consequences of widespread tree mortality triggered by drought and temperature stress. Nat. Clim. Change 3, 30–36 (2013).
38
I. Araujo et al., Trees at the Amazonia–Cerrado transition are approaching high temperature thresholds. Environ. Res. Lett. 16, 034047 (2021).
39
R. Tiwari et al., Photosynthetic quantum efficiency in South-Eastern Amazonian trees may be already affected by climate change. Plant, Cell Environ. 44, 2428–2439 (2021).
40
L. R. V. Zeppetello et al., Large scale tropical deforestation drives extreme warming. Environ. Res. Lett. 15, 084012 (2020).
41
E. W. Butt et al., Amazon deforestation causes strong regional warming. Proc. Natl. Acad. Sci. U.S.A. 120, e2309123120 (2023).
42
J. D. Anadón, O. E. Sala, F. T. Maestre, Climate change will increase savannas at the expense of forests and treeless vegetation in tropical and subtropical a mericas. J. Ecol. 102, 1363–1373 (2014).
43
A. Guha et al., Short-term warming does not affect intrinsic thermotolerance but induces strong sustaining photoprotection in tropical evergreen citrus genotypes. Plant, Cell Environ. 45, 105–120 (2022).
44
L. Zhu et al., Plasticity of photosynthetic heat tolerance in plants adapted to thermally contrasting biomes. Plant, Cell Environ. 41, 1251–1262 (2018).
45
B. C. Posch et al., High-temperature acclimation of photosystem II in land plants. New Phytol. 249, 1108–1123 (2026).
46
A. T. Kullberg, L. Coombs, R. D. Soria Ahuanari, R. P. Fortier, K. J. Feeley, Leaf thermal safety margins decline at hotter temperatures in a natural warming ‘experiment’ in the amazon. New Phytol. 241, 1447–1463 (2024).
47
M. P. Rao et al., Approaching a thermal tipping point in the Eurasian boreal forest at its southern margin. Commun. Earth Environ. 4, 247 (2023).
48
R. K. Braghiere et al., Tipping point in North American Arctic-boreal carbon sink persists in new generation earth system models despite reduced uncertainty. Environ. Res. Lett. 18, 025008 (2023).
49
A. H. Faber, M. Ørsted, B. K. Ehlers, Application of the thermal death time model in predicting thermal damage accumulation in plants. J. Exp. Bot. 75, 3467–3482 (2024).
50
51
Ü. Niinemets, A review of light interception in plant stands from leaf to canopy in different plant functional types and in species with varying shade tolerance. Ecol. Res. 25, 693–714 (2010).
52
O. J. L. Manzi et al., Canopy temperatures strongly overestimate leaf thermal safety margins of tropical trees. New Phytol. 243, 2115–2129 (2024).
53
D. P. Kumarathunge et al., Photosynthetic temperature responses in leaves and canopies: Why temperature optima may disagree at different scales. Tree Physiol. 44, tpae135 (2024).
54
D. L. Cooper et al., Consistent patterns of common species across tropical tree communities. Nature 625, 728–734 (2024).
55
E. Beech, M. Rivers, S. Oldfield, P. Smith, GlobalTreeSearch: The first complete global database of tree species and country distributions. J. Sustain. For. 36, 454–489 (2017).
56
S. Pau, M. Detto, Y. Kim, C. J. Still, Tropical forest temperature thresholds for gross primary productivity. Ecosphere 9, e02311 (2018).
57
S. E. Perkins, L. Alexander, J. Nairn, Increasing frequency, intensity and duration of observed global heatwaves and warm spells. Geophys. Res. Lett. 39, L20714 (2012).
58
R. Teskey et al., Responses of tree species to heat waves and extreme heat events. Plant, Cell Environ. 38, 1699–1712 (2015).
59
D. P. Edwards et al., Conservation of tropical forests in the Anthropocene. Curr. Biol. 29, R1008–R1020 (2019).
60
E. Dinerstein et al., An ecoregion-based approach to protecting half the terrestrial realm. BioScience 67, 534–545 (2017).
61
G. Duveiller, J. Hooker, A. Cescatti, The mark of vegetation change on earth’s surface energy balance. Nat. Commun. 9, 679 (2018).
62
L. Breiman, Random forests. Mach. Learn. 45, 5–32 (2001).
63
D. N. Karger et al., Climatologies at high resolution for the earth’s land surface areas. Sci. Data 4, 1–20 (2017).
64
T. Hengl et al., SoilGrids250m: Global gridded soil information based on machine learning. PLoS ONE 12, e0169748 (2017).
65
N. van Tiel, G. Lenczner, M. Rao, Mukund, C. Grossiord, D. Tuia, Tropical forests are facing increasing risks of exposure to critical temperature thresholds. Zenodo. https://zenodo.org/records/15083361. Accessed 22 June 2026.
66
67
68
N. van Tiel et al., SDM results for 10,590 tree species from “Regional uniqueness of tree species composition and response to forest loss and climate change.” Zenodo. https://zenodo.org/records/10911892. Deposited 3 April 2024.
69
Instagram Engineering
Shopify Engineering