Forests play an important role in efforts to comply with internationally agreed climate targets. Every year, trees capture large amounts of the greenhouse gas CO2 and thus mitigate climate change. Numerous projects are therefore campaigning for the afforestation and replanting of forests in various parts of the world and are supporting the conservation of tropical rainforests. While a number of studies have already examined the effectiveness of the individual measures, there has so far been only little focus on the costs that can be reckoned with. This aspect has now been addressed by a team headed by Kemen Austin of RTI International in the US State of North Carolina.
For their calculations, the researchers took an already existing model representing world-wide forestry and modified it so that they could apply it to assess the effects and costs of various conservation, afforestation and management measures. “The world’s forestry sector can make a really significant contribution to achieving global climate goals,” says Austin’s colleague Justin Baker of RTI International. “The physical potential is there, but if we look at the economic costs, they are not linear. This means that the more we want to reduce emissions, the more expensive this will become.”
For the scenario up to 2055, the forests could contribute ten per cent of required overall reduction, provided that they extract an annual six giga-tonnes of CO2 from the atmosphere. The researchers put the cost of this at 393 billion US dollars (USD) a year.
With this money, financial incentives should for example be provided for land owners and governments to capture an optimum additional amount of CO2 in tree stocks through sustainable forestry. In their calculations, the researchers have assumed an amount of five to 100 USD per tonne of CO2 extracted from the atmosphere in this manner and analysed its respective impact on CO2 reduction.
In the most expensive scenario with the highest CO2 reduction levels, in which new planting of trees and sustainable forest management play an important role alongside conservation measures, the researchers even arrive at costs of 281 USD per tonne of CO2.
The researchers recommend that CO2 prices ought to rise year by year, but would have to be carefully balanced out. Initially, they ought to support the conservation of tropical rainforests in particular, for these forests make by far the largest contribution to capturing CO2. Alone preventing their vanishing would account for 30 to 54 per cent of potential CO2 reduction through forests.
However, replanting of large forest monocultures ought to be financially less attractive. For not only does such intensive use make less sense regarding the climate, it also threatens natural ecosystems. Nevertheless, in scenarios involving high costs and much saving, such measures could make a contribution too, although they should not come first, according to the scientists.
The model which the researchers have compiled also considers that conservation measures in one part of the world have an impact on other regions. For example, if tropical rainforests are only logged to a low degree, this will result in rising timber prices and make tree logging in other areas more attractive. Thus the total impact of the measure is reduced. In the model calculation, this leads to the desired effects having a higher cost.
However, the researchers do not regard such cross-border mutual impacts as problematic. For if the price of CO2 also rises, this will in turn provide a motivation to manage forests particularly sustainably, so that timber extraction and reforestation are in balance.
“In order to avoid the dangerous impacts of climate change, it will be necessary to protect, restore and sustainably manage the world’s forests,” says Austin. “So far, only little research has been conducted on what mitigating climate change with forests costs. A better understanding of costs will help us with prioritising certain resources and developing efficient reduction strategies.”
However, given the fact that even in the most expensive scenario, trees only provide a contribution of around ten per cent of the necessary overall reduction in emissions levels, the researchers also emphasise how important other measures are, such as supporting renewable energy sources, which do not cause greenhouse gas emissions.
(wissenschaft.de, Elena Bernard/ wi)
Kemen Austin (RTI International) et al., Nature Communications, doi: 10.1038/s41467-020-19578-z