Growing trees and then storing the carbon dioxide (CO2) they have taken up from the atmosphere cannot replace cutting emissions from fossil fuel burning, a new study warns. “Reducing fossil fuel use is a precondition for stabilising the climate, but we also need to make use of a range of options from reforestation on degraded land to low-till agriculture and from efficient irrigation systems to limiting food waste,” said Tim Lenton of the University of Exeter in the UK. “If we continue burning coal and oil the way we do today and regret our inaction later, the amounts of greenhouse gas we would need to take out of the atmosphere in order to stabilise the climate would be too huge to manage,” said Lena Boysen from the Potsdam Institute for Climate Impact Research (PIK) in Germany. Plants suck CO2 out of the atmosphere to build their woody roots, stems and leaves. This is low-tech terrestrial carbon dioxide removal that could be combined with high-tech carbon storage mechanisms, for example underground, researchers said.
They calculated that a hypothetically required plantation would in fact replace natural ecosystems around the world almost completely. If CO2 emissions reductions are moderately reduced in line with current national pledges under the Paris Climate Agreement, biomass plantations implemented by mid-century to extract remaining excess CO2 from the air still would have to be enormous, researchers said. In this scenario, they would replace natural ecosystems on fertile land the size of more than one third of all forests we have today on our planet, they said. Alternatively, more than a quarter of land used for agriculture at present would have to be converted into biomass plantations – putting at risk global food security. Only ambitious emissions reductions and advancements in land management techniques between 2005-2100 could possibly avoid fierce competition for land.
However, even in this scenario of aggressive climate stabilisation policy, only high inputs of water, fertilisers and a globally applied high-tech carbon-storage-machinery that captures more than 75 per cent of extracted CO2 could likely limit warming to around 2 degree Celsius by 2100. To this end, technologies minimising carbon emissions from cultivation, harvest, transport and conversion of biomass and, especially, long-term Carbon Capture and Storage (CCS) would need to improve worldwide, researchers said. “What happens in the worst case, a widespread disruption and failure of mitigation policies? Would plants allow us to still stabilise climate in emergency mode? The answer is: no. There is no alternative for successful mitigation,” said Wolfgang Lucht from PIK.
“In such a scenario, plants can potentially play a limited, but important role, if managed well,” Lucht said. Researchers investigated the feasibility of biomass plantations and CO2 removal from a biosphere point of view. So far, biomass plantations as a means for CO2 removal have often been considered as a comparatively safe, affordable and effective approach. “Our work shows that carbon removal via the biosphere cannot be used as a late-regret option to tackle climate change. Instead we have to act now using all possible measures instead of waiting for first-best solutions,” said Tim Lenton of the University of Exeter in the UK. The study was published in the journal Earth’s Future.