Afforestation can provide an important contribution to limiting climate change, as trees take up CO2 from the atmosphere. However, the implementation of relatively cheap afforestation should not lead to lower investments in, for example, renewable energy or the electrification of transport, because, in the long term, complete decarbonisation of the energy system is the solution to reduce greenhouse gas emissions. Moreover, afforestation requires a large amount of land which, in turn, could negatively affect food security.
This is concluded by researchers from PBL Netherlands Environmental Assessment Agency, Utrecht University and Wageningen Economic Research, in their article recently published in Global Change Biology. Afforestation as a solution to climate change is receiving a large degree of attention; for example, as compensation for air travel or by making car fuel CO2-neutral. The study presents a detailed assessment of the potential and costs of afforestation in climate change mitigation. In addition, risks and negative trade-offs for achieving mitigation goals through large-scale afforestation are investigated.
Afforestation is relatively cheap, but involves risks for food security
The study shows that afforestation is already profitable at a relatively low price: by 2050 it would be possible to take an annual 1.5 GtCO2 (gigatonnes of CO2) out of the atmosphere for as little as USD50/tCO2. This implies that the cost-effective implementation of a 2 °C climate target could lead to large-scale afforestation by the end of this century. Under such a scenario, there is cumulative sequestration of 410 GtCO2 from afforestation until the end of the century. Over 50% of this sequestration takes place in Latin America and Sub-Saharan Africa. This is a risk because long-term sequestration of CO2 depends on the quality of governments in these regions. In addition, afforestation would require large amounts of land; as much as 11 million km2 under a 2 °C scenario. In comparison, current global cropland amounts to nearly 16 million km2. If no additional measures are taken, such as increased efficiency in agriculture or dietary changes, the increasing demand for land could result in negative effects on food production, in turn, leading to food shortages and famines.
Considering negative trade-offs of afforestation is crucial
A recent article in Science by Jean-Francois Bastin (and others) from the Crowther Lab of ETH Zürich argues that afforestation is the best way to mitigate climate change. It finds a cumulative potential of 730 GtCO2 from afforestation, which is substantially more than the 410 GtCO2 from the study by PBL, Utrecht University and Wageningen Economic Research. Bastin does not take into account the trade-offs of afforestation with food security nor does he consider the risks for general mitigation strategies to achieve stringent climate targets. The study by PBL, Utrecht University and Wageningen Economic Research indicates that it is crucial to develop policy that takes into account the risks and trade-offs of afforestation in order to sustainably mitigate climate change.