As global temperatures rise, a tipping point will be reached where trees will emit more carbon than they take in through photosynthesis, a study suggests.
Katharyn Duffy Photo: supplied
Northern Arizona University earth systems scientist Dr Katharyn Duffy led the study, published in Science Advances, which was done in collaboration with the University of Waikato.
Plants, like living beings, struggle when temperatures accelerate.
“Nature is an amazingly efficient machine ... but these trees are still living things that are susceptible to physical limitations and so we actually need to do both – to plant trees … but we need to look at ourselves and reduce our own emissions,” Duffy told Kim Hill.
Climate change is rapidly pushing temperatures to the point it’s affecting photosynthesis, she says.
“Every time we put out one tonne of carbon dioxide, plants pick up 30 percent. Plants are currently mitigating climate change and giving us an ecosystem service that is slowing global warming.
“What we published in this paper is showing that we are rapidly entering climate spaces where plants may slow that discount on carbon emissions and or reverse it, because that carbon they store in their trunks and soils is vulnerable to release.”
The study didn’t initially go looking for ‘the tipping point’ but in their journey to seek a temperature dependence curve for the terrestrial biosphere, the researchers wondered ‘how close are we to the temperature maximum of photosynthesis’.
“We realised we were actually beginning to cross that threshold over the last decade, which was the warmest decade on record.
“Something that’s a little frightening is that the Amazon and some of the boreal forests and taiga forests in Russia, two incredibly productive ecosystems … those are two of the ecosystems that actually cross their temperature tipping point quite early.”
That has major implications for how much carbon is cycled and stored, she says. One way to mitigate the impacts is to restore ecosystems and make them more resilient to climate change, she says.
“We need to really think about protecting some of these really rich diverse and productive biomes.”
The problem with biomes that have adapted photosynthesise at higher temperatures is that they store and cycle less carbon, she says.
“So it’s not the photosynthesis stop, it’s just how much carbon terrestrial biosphere will continue to take in and then store.
“Given temperature tipping points, there will be some shifts in ecosystem distribution such that those ecosystems will align with future climate, that will be a kind of chaotic and mess process and will likely alter how much carbon is taken up still.”
In addressing climate change, we also need to be aware how fragile the ecosystem is, she says.
“Seedlings we plant today may be under pretty extreme temperature stress in a couple of decades unless we are actively mitigating climate change today and that really needs to focus on emissions reductions.”
