Predicted CO2 levels cause marked increase in forest temperatures

(Press-News.org) Elevated carbon dioxide levels generated as a result of climate change could significantly increase the temperatures found within the canopies of the world’s woodlands and forests, new research has suggested.

A study by researchers from the UK, Ghana and the USA used thermal imaging technology and other sensors to measure the leaf temperatures found at CO2 levels forecast to occur in 2050.

It found that temperatures within the forest canopies rose by around 1.3°C as a direct consequence of increases in CO2 – from an average of 21.5°C under current conditions to 22.8°C at the predicted 2050 CO2 levels.

However, the difference was even more noticeable in extreme heatwaves – as experienced in the UK in the summer of 2022 – where the difference was more than 2°C and the highest recorded leaf temperature rose to around 40°C.

This, the researchers say, is likely caused by reduced levels of transpiration – the process through which water is loss from plants through evaporation from stomatal pores – as plants alter their physiology to reduce water loss when growing in environment where CO2 is elevated.

They believe that as well as having a direct impact on leaf pore structure, it could impact trees’ ability to transmit water back into the environment, which would have a knock-on effect on the water cycle globally.

The researchers say their findings emphasise the importance of cutting global CO2 emissions particularly at a time when there are widespread calls to plant more trees to benefit the environment. And while they believe oak trees may be to some extent resilient to the changes predicted to occur, the impact on other species is likely to be more marked.

The study, published in the journal Global Change Biology, was led by researchers at the University of Plymouth working alongside partners from the University of Birmingham, University of Leeds, Northern Arizona University, and the Forestry Research Institute of Ghana.

Dr Sophie Fauset, Associate Professor in Terrestrial Ecology at the University of Plymouth and the study’s senior author, added: “We are increasingly relying on trees to mitigate against future environmental change, but this study shows how the changes already happening are having a negative effect on our forests. Our findings are clear evidence that leaf temperature is going up simply as a consequence of increased CO2 and regardless of any other factors. Our tree populations have adapted to their environments over many centuries, but whether they will continue to do so at a time of such swift environmental change is an obvious cause for concern.”

The research was carried out at the University of Birmingham Institute for Forest Research Free Air CO2 Enrichment (BIFoR-FACE) facility in Staffordshire, England, during the growing seasons of 2021, 2022 and 2023.

As different levels of CO2 were pumped into the forest, a thermal imaging camera fixed to a tower within the canopy captured infrared images every 10 minutes for around 22 months.

The experiment also coincided with a period in which the UK experienced its hottest year on record, including a summer heatwave in 2022 where air temperatures exceeded 40°C for the first time.

It provided researchers with huge quantities of data about the precise temperatures being experienced within the forest canopy at differing CO2 concentrations and environmental conditions.

The project forms part of ongoing research by the University, and partners in the UK and worldwide, which has shown that some forests are already reaching, and occasionally exceeding, the temperatures at which they can no longer function.

William Hagan Brown, a PhD researcher at the University of Plymouth and the Forestry Research Institute of Ghana, is the study’s lead author. He added: “As well as this study, we are currently running a similar project in Ghana. Our overall aim is to try and understand how canopy temperatures vary among types of trees and in different locations over the seasons. While we believe the oak trees that formed the main focus of the research are broadly resilient, the shifts in our climate could impact other species to a far greater extent. That is something we need to understand to ensure we can plant new trees, and ensure existing populations survive in the future.”

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