Large-scale afforestation and reforestation can curb global warming

The Paris Agreement calls on us to limit global warming to 1.5 degrees Celsius above pre-industrial levels. To achieve this goal, we need to reduce CO₂ emissions and remove existing CO₂ from the atmosphere.

A team led by LMU scientists Yiannis Moustakis and Julia Pongratz has now demonstrated that large-scale afforestation/reforestation (AR) can make an important contribution to such efforts. Simulations performed by the researchers show that AR could reduce peak and end-of-century temperatures and shorten the period in which global temperatures exceed the 1.5 degree target, as they report in the journal. Natural communications.

AR is currently the most frequently deployed method for removing carbon dioxide from the atmosphere. “Overall, the international community has already announced ambitious energy reduction targets of up to 490 million hectares by 2060, and this figure is likely to increase further as more countries present their plans in the long term. We wanted to know how effective these measures can be. influence the climate,” explains Moustakis.

“Studying their effects in detail requires the use of state-of-the-art models that can represent an interactive carbon cycle taking into account various processes and feedbacks.”

Modeling with over 1,200 scenarios

The researchers used an unprecedented number of more than 1,200 scenarios from Integrated Assessment Models (IAM) – models that link climate policies to future energy, economic and land use pathways – as well as maps of restoration priorities and biodiversity data to develop an ambitious AR scenario. . Scientists were thus able to take into account the technical and economic challenges, while also considering the impact on biodiversity and land availability in the countries.

On this basis, the researchers developed a scenario that predicts 595 million hectares (Mha) of forested/reforested land by 2060 and 935 Mha by 2100.

“This is undoubtedly an ambitious scenario, and one could of course question the feasibility of such ambitious efforts. However, this is not an arbitrary choice. We have tried to develop a scenario that rather falls within the range of commitments of countries on a global scale, to extend it to the end of the century, and constrain its spatial and temporal characteristics by technical-economic considerations, while minimizing the impact on biodiversity. , underlines Moustakis.

Next, the scientists analyzed this AR scenario with the Max Planck Institute for Meteorology’s Earth System Model, which can simulate the effects of afforestation/reforestation on the climate. The simulations used an overshoot scenario, that is to say a climate scenario where the trajectory of emissions is such that the global average temperature exceeds the objective of 1.5°C before falling below this level towards the end of the century.

“As delays in draconian climate measures persist, such scenarios become increasingly likely,” says Moustakis.

The average temperature falls, the duration of the exceedance shortens

Simulation results show that ambitious AR measures could significantly influence the climate. Specifically, AR could reduce the global maximum temperature by mid-century by 0.08°C, while lowering the end-of-century temperature by 0.2°C compared to a scenario without AR. Additionally, these measures could reduce by 13 years the period in which global temperatures exceed the 1.5 degree target. The AR footprint on global temperature will become evident by 2052.

Another important finding from the simulations is that the secondary effects of AR on climate do not exceed their positive effects linked to CO absorption.₂: AR not only has effects on carbon sequestration, but also changes physical properties of the Earth’s surface, such as albedo (the ability of the Earth’s surface to reflect sunlight) and l evaporation of water. This may lead to warming in some areas. But as the study shows, the cooling effect of CO₂ absorption predominates, because the local warming caused by AR is not strong enough to cancel out the cooling effect.

“These results show that global AR can actually make an important contribution to climate change mitigation when applied at scale,” says Moustakis. “But it is not a panacea and must be considered in a more global framework that also takes into account socio-economic trade-offs.

“Planting a forest could create jobs, income and promote ecosystem services, but it could also deprive people of their livelihoods, exacerbate poverty, displace people financially or physically and disrupt local food networks. “