Forestation found to have 'side-effects', could offset CO2 removal gains

New Delhi: Large-scale forestation, recognised as one of the essential carbon removal strategy to mitigate climate change, has been found to have "side-effects" that could offset the benefits by a third.

Researchers have found that while forestation - converting bare or cultivated land into forests - helps in increasing carbon dioxide absorption from the atmosphere, there are other complex Earth System responses at play that could reduce these gains.

Earth System science assumes a holistic view of the dynamic interactions between various Earth's spheres like atmosphere, biosphere, hydrosphere and others, and their many constituent subsystems fluxes and processes.

This study, led by the University of Sheffield, UK, found that some of these complex responses offsetting the CO2 removal benefits included reduced reflectivity of the land surface and changes to the atmospheric concentrations of other greenhouse gases like methane and ozone, termed "indirect effects" of forestation by the researchers.

They also found, however, that when forestation was implemented alongside other strategies to tackle climate change, such as reducing fossil fuel emissions, the negative impacts of these indirect effects were lower.

The findings suggested that the benefits of wide-scale forestation efforts may be overestimated and highlighted the importance of combining these efforts with complementary climate change mitigation strategies for more effective long-term action, the researchers said.

"Many businesses now offer to plant a tree with a purchase, and some countries plan to expand, conserve, and restore forests. Trees can help tackle climate change, but we need to be careful about relying on them.

"We need to evaluate forestation, and other climate change mitigation strategies, in detail. This will help identify limitations and unintended consequences so these can be minimised where possible," said James Weber from the University of Sheffield's School of Biosciences and lead author of the study published in the journal Science.

For the study, the researchers simulated wide scale forestation under two future scenarios - one with minimal efforts to tackle climate change and another with extensive mitigation measures alongside forestation.

"We know that forests are critically important for biodiversity, water, ecosystem services, and the climate. What this research shows is that the effectiveness of reforestation for climate mitigation declines significantly in higher latitudes and unless paired with deep emission reductions which reduce air pollution," said study co-author Stephanie Roe, World Wildlife Fund (WWF) Global Climate and Energy Lead Scientist, and lead author of the Intergovernmental Panel on Climate Change's (IPCC's) Sixth Assessment Report.

Preventing deforestation, when compared to reforestation efforts, is a far more efficient way to mitigate climate change, added Roe.

Further, the study critically showed that not all forestation is equal, with more favourable potential in the tropics, whereas forestation at higher latitudes may well result in net global warming, according to David Edwards, Head of Tropical Ecology and Conservation Group at the University of Cambridge, UK, and not involved in the study.