Maximum global forest carbon sink for climate change mitigation

Background/Question/Methods

Global forests have provided valuable ecosystem services over decades by sequestering a huge amount of carbon and reducing CO₂ buildup in the atmosphere. In this study, we estimated the maximum global forest carbon sink based on various data sources.  Our earlier study showed that the carbon sink in the global established forests was 2.4 PgC yr^-1, equal to 33% of fossil fuel emissions, or 24% of anthropogenic emissions. If we also count the carbon sink in tropic regrowth forests recovered from deforestation, the global forest carbon sink could reach 4.0 PgC yr^-1, literally the half of global fossil fuel emissions in the last decade.  Besides tropical deforestation driven by agricultures, commercial logging and particularly illegal logging in tropical forests also contribute considerably to carbon emissions, although they are usually under reported and difficult to measure. The logging activities not only extract wood and cause emissions during processing, also damage surrounding forests and trigger fires to cause higher emissions. The under-reported carbon emissions from logging activities were estimated to be 1.0 PgC yr^-1.  To balance the global carbon budget would require an extra sink of 1.0 PgC yr^-1 in disturbed forests, making the global forest carbon sink as high as 5.0 PgC yr^-1. Additionally, there are other potentials to enhance global forest carbon sinks such as afforestation and improved forest management. We estimate that 6.0 PgC yr^-1 would be the maximum C sink that global forest ecosystems may achieve.  

Results/Conclusions

To fully take advantage of this valuable potential forest C sink for climate mitigation, the precondition is to significantly reduce or eliminate deforestation and forest degradation in tropics.  The United Nation’s REDD+ program was designed to conserve tropical forests and reduce relevant emissions, offering financial incentives to tropical developing countries for their efforts to pertain REDD+.  Although completely  halting tropical deforestation and forest degradation is unrealistic, if tropical deforestation could be reduced by half under the REDD+ mechanism and if more sustainable logging techniques could be implemented, we may expect to reduce altogether 2.0 PgC yr^-1 out of 3.8 PgC yr^-1 C emissions in the forest sector. This  would leave a net global forest carbon sink at 4.2 PgC yr^-1, sufficient to offset more than 40% of global fossil fuel emissions today.  However, even to achieve this halfway goal, there are tremendous challenges facing our societies, demanding commitments across all the levels from local communities to country’s good governance.