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In the past, intact forests absorbed 7.8 billion tonnes of CO₂ annually – about a fifth of all human emissions – but their carbon storage is increasingly at risk from climate change and human activities such as deforestation.
A new study from the Potsdam Institute for Climate Impact Research (PIK) shows that failing to account for the potentially decreasing ability of forests to absorb CO₂ could make reaching the Paris Agreement targets significantly harder, if not impossible, and much more costly.
“Delaying action leads to disproportionately higher costs,” explains Michael Windisch, lead author of the study published in Nature Communications and PIK guest scientist.
“Right now, our climate strategies bet on forests not only remaining intact, but even expanding,” Windisch says, adding: “However, with escalating wildfires like in California, and continued deforestation in the Amazon, that’s a gamble. Climate change itself puts forests’ immense carbon stores at risk.”
According to the study, postponing action to reduce emissions and to protect and monitor forests could jeopardise climate targets.
“We must act immediately to safeguard the carbon stored in forests,” Windisch emphasises. “Otherwise, compensating for potential forest carbon losses through steeper emissions cuts in key emission sectors like energy, industry and transport will become increasingly expensive and possibly unattainable.”
Considering forest carbon losses in climate mitigation pathways
The study analysed how climate targets can be met despite forests’ reduced capacity for storing carbon. The authors used REMIND-MAgPIE – an integrated global land and water use modelling as well as an energy-economy modelling system – together with the global vegetation model LPJmL to evaluate how natural disturbances and human impacts on forests influence the feasibility of achieving climate mitigation goals. The research team compared a foresighted policy response with various delayed and myopic approaches.
Regardless of the assessed disturbance rate, the study revealed just how steep the price of inaction can be. Even a five-year delay in responding to forest carbon loss would lead to a roughly two-fold increase in both the stringency and overall cost of measures to offset that lost carbon, the authors find.
Emission cuts in the energy sector, for instance, would have to be ramped up considerably, supported by a near-doubling of negative emissions capacity – which itself demands a corresponding expansion in land use. Ultimately, these extra efforts drive up overall costs, and result in GDP setbacks that are approximately double those of immediate action.
The study also highlights that current models may be overly optimistic about future forest carbon storage because they ignore disturbances, overvalue CO₂ fertilisation and underestimate deforestation. To mitigate climate impacts, safeguard carbon stocks and prevent escalating costs, the scientists recommend immediate action.
“Forests are not an infinite resource but need careful monitoring to detect reductions in carbon sinks early on,” explains Florian Humpenöder, PIK scientist and study author.
He also stresses the need for stronger forest conservation, and faster decarbonisation. Forests may absorb less CO2 than expected, making realistic forest carbon projections essential.
“Staying below critical warming thresholds requires more than just hoping forests will remain intact,” concludes Alexander Popp, head of PIK’s Land Use Transition lab and author of the study. “Alongside protecting forests, it is essential to promote sustainable land use practices– not only to preserve biodiversity but also to avoid drastic economic consequences and to secure our climate future.”
