Forests “Flatline” On Trapping Carbon Dioxide With Temperature Rise, Study Shows
December 18, 2013

Forests “Flatline” On Trapping Carbon Dioxide With Temperature Rise, Study Shows

Ranjini Raghunath for – Your Universe Online

A four-degree-Celsius rise in the Earth’s surface temperature could max out the amount of carbon dioxide that forests can trap from the atmosphere, according to new research by a team of European researchers.

Rainforests, such as the Amazon, act as natural carbon “sinks,” using up and storing carbon dioxide (CO2) from the air to make food. While humans continue to pump CO2 into the atmosphere, these sinks help maintain a balance by absorbing up to half of the total CO2 emitted globally.

The key factor that decides how Earth’s plants and forests will respond to higher carbon dioxide levels is how long CO2 remains trapped in the plants during its lifecycle – known as “residence time,” researchers report.

As CO2 content in the atmosphere increases, initially, forests will take up more CO2 and make more food. But as temperatures continue to rise, plants begin experiencing stress, lose their ability to retain water and CO2, and at one point, “flatline” – reaching a point where they can’t take up any more CO2.

With nowhere to go, CO2 content in the atmosphere would increase, heating up the Earth, which would cause more drought and forest fires, which in turn would lead to less forest cover to take up CO2.

As negative effects of climate change continue to increase, CO2 will spend less and less time in plants and escape quickly to the atmosphere where it could continue wreaking havoc over the Earth’s climate.

"In heat waves, ecosystems can emit more CO2 than they absorb from the atmosphere," said Andrew Friend, lead author and University of Cambridge researcher, in a press release. "We saw this in the 2003 European heatwave when temperatures rose six degrees above average - and the amount of CO2 produced was sufficient to reverse the effect of four years of net ecosystem carbon sequestration."

The researchers used seven climate models to predict how plant life would respond to possible climate scenarios with different levels of greenhouse gases. Using supercomputers that cut months of work down to days, they studied how plants would grow, make food, and compete with other plants in different climate and soil conditions.

“We then input real climate data up to the present and look at what might happen every 30 minutes right up until 2099,” Andrew Friend, lead author said, in a press release.

Although there were some differences in predictions between the models, most agreed on the two key findings – the four-degree saturation point and “residence time” as the deciding factor for plants’ tolerance levels.

"The idea here is to understand at what point the increase in global temperature starts to have serious effects across all the sectors, so that policy makers can weigh up impacts of allowing emissions to go above a certain level, and what mitigation strategies are necessary,” Friend said.

Negative effects on plants will also have ripple effects on animal life and the entire food chain that depends on them, he stated.

The researchers suggest more attention needs to be diverted to studying these plant-carbon interactions and the effects on their food-making machinery, rather than simply focusing on planting more trees. Also important is how different plants retain CO2 differently and how this impacts the overall CO2 balance, they suggest.

The study was part of a project bringing together scientists from eight countries to study climate change impacts, called the 'Inter-Sectoral Impact Model Intercomparison Project' (ISI-MIP). The results were published in the journal Proceedings of the National Academy of Sciences.