There’s something you must know about trees and their role in climate change

You may have heard the tired argument that if carbon dioxide levels are going up, it’s going to be great for boosting the growth of trees. It’s true – to an extent. But there’s a really important detail we must not miss.

Plants, including trees, are growing faster thanks to what is known as the carbon fertilisation effect, but past studies have already suggested that this phenomenon may only be temporary.

A new study has now revealed the potential limits of carbon fertilisation – specifically whether plants are likely to reach a tipping point: when we can no longer expect increasing CO2 to mean increasing plant growth.

“Over the last three or four decades, forests and terrestrial systems in general have absorbed almost a quarter of all fossil fuel emissions released into the air,” Earth system scientist Rob Jackson told Newsweek.

“A large part of that gain has been because of carbon dioxide fertilisation (carbon dioxide as plant food). Will this extra growth continue?”

The researchers looked at 138 past experiments which focussed on elevating carbon dioxide levels in a small area – everything from grassland, shrubland, and cropland to forest systems.

Their analysis included a range of statistical methods, machine learning, computer modelling and satellite data to arrive at a measure of how much soil nutrients and climatic factors can affect the ability of plants to absorb extra carbon dioxide.

This is important, because plants don’t just use carbon dioxide for their growth. They also need a lot of other factors and key nutrients, especially phosphorus and nitrogen.

“The strength of CO2 fertilisation is primarily driven by nitrogen in ~65 percent of global vegetation and by phosphorus in ~25 percent of global vegetation,” the researchers explain in their paper.

“Our approach suggests that CO2 levels expected by 2100 can potentially enhance plant biomass by 12 percent above current values.”

In a way, this could be good news. That immediate capacity to soak up carbon dioxide means we have a little bit of time to make good use of the amazing carbon sequestering ability of trees – at least until the end of the century.

Beyond 2100, however, whether forests will retain this carbon dioxide absorbing ability is unclear.

The findings do give us even more reason to look after the forests and plants we already have, and replant trees in areas that have been cleared, sooner rather than later.

“We have already witnessed indiscriminate logging in pristine tropical forests, which are the largest reservoirs of biomass on the planet,” says environmental scientist César Terrer from Stanford University. ”We stand to lose a tremendously important tool to limit global warming.”

However, a lot of excess carbon dioxide is still ending up in the atmosphere, heating the planet and melting the ice caps. We can’t expect plants to do all the work for us. We will still need to put pressure on policy makers to implement changes, and lower our own environmental footprint – especially when it comes to releasing carbon dioxide.

But it is helpful to know that, for now, trees have got our back.

“Planting or restoring trees is like putting money in the bank,” said Jackson. ”Extra growth from carbon dioxide is the interest we gain on our balance.”

While trees alone aren’t going to save us, right now they might well be pivotal in our battle to limit the worst effects of climate change in the short term.

“Keeping fossil fuels in the ground is the best way to limit further warming,” says Terrer.

“But stopping deforestation and preserving forests so they can grow more is our next-best solution.”

The research has been published in Nature Climate Change.

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