Scientists discover rising heat leaves trees struggling to turn sunlight into energy: 57 million hectares of tropical forests already affected; Heat waves goes beyond photosynthesis limits

Tropical forests, often called the planet’s natural carbon sinks, are facing a new climate challenge as rising temperatures begin affecting their ability to photosynthesise efficiently, according to a new study published in the Proceedings of the National Academy of Sciences (PNAS).

Researchers found that around 57 million hectares of tropical forests are now experiencing temperatures that interfere with the process through which trees convert sunlight into energy while absorbing carbon dioxide from the atmosphere.

The affected area has grown significantly over the past two decades, raising concerns that continued warming could weaken one of Earth’s most important natural systems for regulating climate.

Why are tropical forests struggling with rising temperatures?

Trees depend on photosynthesis to survive, grow and store carbon. However, like all living organisms, plants can function effectively only within a certain temperature range.

The study found that when leaf temperatures rise beyond a critical point, the proteins involved in photosynthesis begin to break down. As a result, trees become less efficient at producing energy, slowing their growth and making them more vulnerable to stress, diseases and even death.

Scientists warn that repeated exposure to extreme heat could gradually weaken entire forest ecosystems.

How many tropical forests have crossed dangerous heat levels?

Researchers analysed satellite-based temperature observations collected between 2001 and 2020 along with heat tolerance information from nearly 200 tropical plant species.

The findings showed that the area of tropical forests experiencing canopy temperatures above their average critical threshold increased from 43 million hectares to 57 million hectares.

The affected area is roughly comparable to the size of France.

This increase suggests that more tropical forests are being exposed to conditions that could reduce their ability to function normally.

What happens when photosynthesis slows down?

Photosynthesis is the process that allows trees to absorb carbon dioxide and release oxygen. It also helps forests act as a major buffer against climate change by storing carbon.

But when excessive heat reduces photosynthetic activity, forests capture less carbon from the atmosphere.

This could create a worrying cycle where rising temperatures weaken forests, and weaker forests become less capable of slowing down further warming.

Scientists warn the problem could grow in coming decades

The researchers projected that the situation could become more severe if global temperatures continue rising.

According to the study, the area of tropical forests experiencing temperatures beyond critical limits could expand to around 93 million hectares by 2050.

By 2100, the affected area could reach 160 million hectares, an area close to the size of South Africa.

These projections highlight how climate change could reshape some of the world's most important ecosystems over the coming decades.

Why does forest heat stress threaten wildlife too?

The impact of rising temperatures may not be limited to trees.

As some plant species struggle to survive, forests could gradually see changes in their composition, with heat-tolerant species replacing those that cannot withstand extreme conditions.

Such changes could affect countless animals that depend on specific trees for food, shelter and breeding habitats.

Birds, mammals, insects and other species that rely on tropical forests could face disruptions as ecosystems change.

Could tropical forests lose their role as carbon sinks?

Tropical forests currently absorb large amounts of carbon dioxide every year, helping reduce the amount of greenhouse gases in the atmosphere.

However, if heat stress continues to reduce photosynthesis, these forests may absorb less carbon in the future.

Researchers also warned that extreme heat could affect other natural processes, including the release of water vapour by forests. Reduced moisture could contribute to higher risks of drought and extreme weather events in some regions.

Can tropical forests adapt to a warmer planet?

Despite the concerns, scientists said some tropical tree species may have the ability to adapt to changing temperatures.

Over time, heat-resistant species could become more dominant, helping forests survive in a warmer climate.

However, researchers cautioned that it remains uncertain whether natural adaptation can happen quickly enough to match the speed of human-driven climate change.

Identifying forests most vulnerable to rising temperatures could help conservation efforts and protect ecosystems that play a crucial role in maintaining global climate balance.

(With TOI inputs)