Temperates reaching tipping point where plants will no longer produce building block for life on earth, study warns

Small but significant proportion of leaves in tropical canopies are experiencing temperatures of 46.7C or above, at which point their survival is threatened

People walking along the tropical rainforest beach in Tortuguero with beautiful palm trees and turquoise water, Costa Rica, Central America (Getty Images)

A significant number of trees in tropical ecosystems are being subjected to a dangerously high temperature threshold where the process of photosynthesis begins to fail, new research has found.

The study published in the journal Nature says the impact of high temperatures is already visible on plants, and a small but significant percentage of leaves within these vital ecosystems are teetering on the brink of the critical temperature threshold, which could have far-reaching consequences for their survival.

The study reveals that an estimated 0.01 per cent of leaves in the upper canopies of tropical forests are currently experiencing temperatures that surpass the critical threshold for photosynthesis to function properly.

This threshold, around 46.7C on average, marks the point at which the photosynthetic machinery within tropical trees begins to deteriorate, threatening their survival.

Tropical forests, often referred to as the lungs of the Earth, play a key role in absorbing carbon dioxide and supporting a vast array of biodiversity. However, the delicate balance of these ecosystems is under threat as global temperatures continue to rise.

“Breaching the thresholds for thermal viability of the tropical forest biomes, home to most of the planet’s biodiversity, could be considered a major tipping point for the Earth’s biosphere,” Dr Yadvinder Malhi, professor of ecosystem science, University of Oxford, said.

“By looking at how leaf temperatures vary within and across forest canopies, this study offers novel new insights that this threshold is closer than we thought, but also that it is entirely within our collective means to navigate away from this dangerous threshold.”

The study, led by Christopher Doughty and a team of researchers, utilised high-resolution measurements of land surface temperatures across various tropical forest regions, including Brazil, Puerto Rico, and Australia.

These measurements were collected between 2018 and 2020 using an instrument onboard the International Space Station.

Explaining about the impact of reduced photosynthesis, Dr Kevin Collins, senior lecturer environment and systems, The Open University says: “For humans, a reduction in photosynthesis could lead to reduced harvests, especially in warmer climates. Tropical forests are also key climate regulators of regional and global climate and any stress on them adds to the effects of climate change.”

While the study confirms that the majority of tropical forest canopy temperatures peak at an average of 34C, it also highlights that a small fraction of observed areas exceed the concerning 40C mark.

What's more alarming is that these numbers are predicted to escalate under future heating conditions. The researchers' modelling efforts forecast that the proportion of leaves experiencing these perilous temperatures could rise from 0.01 per cent to 1.4 per cent.

The study's models suggest that if global warming surpasses 3.9C—an extreme scenario—large-scale leaf death and loss within tropical forests could become a reality.

While the results of the study currently show a small percentage of plants undergoing this impact, scientists warn this number could increase in the future.

“Although the proportion of leaves being talked about may seem small at first glance, it is another indication that as climate change intensifies, we risk upsetting the natural environments on which we rely,” Dr Leslie Mabon, lecturer in environmental systems, The Open University, said.

“This is why it is so important that we do everything we can to avoid the uncertainties associated with higher levels of global heating, by reducing the burning of fossil fuels and preventing deforestation.”