Is tree planting an effective strategy for climate change mitigation?

Carbon stock projection for four major forest plantation species in Japan

Carbon sequestration via afforestation and forest growth is effective for mitigating global warming. Accurate and robust information on forest growth characteristics by tree species, region, and large-scale land-use change is vital and future prediction of forest carbon stocks based on this information is of great significance. These predictions allow exploring forestry practices that maximize carbon sequestration by forests, including wood production. Forest inventories based on field measurements are considered the most accurate method for estimating forest carbon stocks. Japan's national forest inventories (NFIs) provide stand volumes for all Japanese forests, and estimates from direct field observations (m-NFIs) are the most reliable. Therefore, using the m-NFI from 2009 to 2013, we selected four major forest plantation species in Japan: Cryptomeria japonica, Chamaecyparis obtusa, Pinus spp., and Larix kaempferi and presented their forest age-carbon density function. We then estimated changes in forest carbon stocks from the past to the present using the functions. Next, we investigated the differences in the carbon sequestration potential of forests, including wood production, between five forestry practice scenarios with varying harvesting and afforestation rates, until 2061. Our results indicate that, for all four forest types, the estimates of growth rates and past forest carbon stocks in this study were higher than those considered until now. The predicted carbon sequestration from 2011 to 2061, assuming that 100 % of harvested carbon is retained for a long time, twice the rate of harvesting compared to the current rate, and a 100 % afforestation rate in harvested area, was three to four times higher than that in a scenario with no harvesting or replanting. Our results suggest that planted Japanese forests can exhibit a high carbon sequestration potential under the premise of active management, harvesting, afforestation, and prolonging the residence time of stored carbon in wood products with technology development.

The scientific basis of 'net zero emissions' and its diverging sociopolitical representation

The Net Zero Emissions (NZE) concept has created momentum for climate commitment made by national governments, cities, industries and individual companies. However, evidence of tangible decarbonisation is limited. Here we identify precarious differences between the scientific origin of NZE and its social representation in the wider public and explore the consequences of the resulting science-action gap for achieving global climate goals. A particular focus is given to 'offsetting', which is closely connected to the practical delivery of NZE but typically ignores that different types or carbon credits have different environmental efficacy. Revisiting the science related to the global carbon cycle demonstrates that a heavy reliance on any carbon offsetting that is not a permanent removal presents a real risk. Moreover, competition over scarce 'removal credits' distracts from the real tasks at hand, namely to rapidly decrease fossil fuel emissions, actively remove carbon through restoration, and protect existing terrestrial carbon sinks. Establishing separate targets for these distinct actions is an essential step towards disentangling current confusion. Whilst a 'race to net zero' may trigger innovation in the decarbonisation space, the restoration and protection of carbon sinks demands a collective approach where actors should focus on how to make real and verifiable contributions rather than claiming individual net zero scores.