The preservation and reforestation of forests is considered an important measure to bind more carbon dioxide from the atmosphere. Now researchers have determined where in the world forests and soils could still absorb additional CO2, how much of it and by what means. Their world map shows that the potential for such CO2 binding has not yet been exhausted, especially in the tropics. In total, global forests and soils could absorb an additional 287 billion tons of carbon. The preservation and targeted care of existing but degraded forests have more potential than afforestation – also because the latter entails conflicts with food production.
Forests and soils are important greenhouse gas sinks in the climate system – they store carbon in the form of biomass and organic material and thus remove it from the carbon cycle and above all from the atmosphere. The most recent world climate report and many studies have already shown that such natural CO2 sinks also play an important role in climate protection. In the meantime, climate change has progressed so far that a reduction in CO2 emissions alone will not be enough to achieve the climate protection target of a maximum of two degrees warming compared to pre-industrial times. In addition, strategies to remove CO2 from the atmosphere are required. “CO2 storage in woody biomass, such as forest ecosystems, is generally considered to have a particularly high potential, especially as it also brings a number of ecological and socio-economic benefits,” explain Wayne Walker from the Woodwell Climate Research Center in Massachusetts and his colleagues.
There is still untapped storage potential
The researchers have now examined more closely how high the still unused potential for CO2 storage in forests and soil is. “Terrestrial ecosystems store enormous amounts of carbon every year,” explains Walker. “But in order to be able to use the still untapped potential of these systems for climate protection, we have to know how much storage space is still available, where in the world this space is and with which measures we can use this potential as quickly as possible.” team has developed a model based on global data sets that shows the previous and still available CO2 absorption capacity of trees, tree roots and soils worldwide. Their world maps illustrate this potential with a resolution of 500 meters and for the present and for a future with unchecked climate change.
The evaluation showed that forests and soils worldwide already store around 3.4 trillion tons of carbon – this corresponds to around 88 percent of the maximum possible. “This leaves a deficit of 12 percent, or 494 billion tons of carbon, as potential for additional CO2 uptake,” Walker and his team write. Almost three quarters of this unused potential lies in the above- and below-ground tissues of the trees. If one subtracts the land areas that are required for agricultural food production and for settlement areas from this maximum potential, there are still 286.7 billion tons of unused storage potential in forests and soil, as the researchers report.
Optimized forest management more effective than afforestation
The natural CO2 storage potential is not evenly distributed over the earth: “Of the three large bioclimatic zones, the tropics and subtropics contain by far the largest proportion of unused carbon storage at 68 percent,” write the scientists. “That’s five times more than the temperate zone and 3.5 times more than the boreal and polar zones.” If you look at the distribution of this CO2 sink across the individual countries, half of the untapped potential lies in just seven countries: Russia, Brazil , the US, China, the Republic of the Congo, Indonesia and Canada. According to the team, the boreal forest areas of Russia alone contain around 15 percent of the global potential. However, if the values are converted to unused storage potential per area, tropical countries such as the Philippines, Indonesia, Myanmar and Tanzania are ahead.
The study also shows which measures can best and fastest bring the still free storage capacities to an additional intake of CO2. According to this, the most effective solution is not the afforestation of cleared or only sparsely treed areas, but the improved management of existing but degraded forests. In the tropics, 70 percent of the untapped potential could be used in this way alone – five times more than through the reforestation of new tropical forests, as Walker and his colleagues have determined. In Brazil, for example, more than half of the CO2 storage capacity that is still available there could already be achieved through better management of the forests, especially in the Amazon region. “Forest protection represents the greatest opportunity to bind and store carbon in a timely manner. The urgency of the climate crisis therefore requires that we prioritize such actions,” says co-author Peter Ellis of The Nature Conservancy in Virginia.
According to the research team, their maps and data can now provide very practical help in identifying the cheapest and most effective measures for different regions and countries. “Our results will be valuable for many countries, because such natural solutions contribute greatly to meeting the targets of the Paris climate agreement,” says Ellis’ colleague Bronson Griscom.
Source: Wayne Walker (Woodwell Climate Research Center, Falmouth, Massachusetts) et al., Proceedings of the National Academy of Sciences, doi: 10.1073/pnas.2111312119