Fossil fuels, worldwide, currently contribute about 90% of the carbon emissions from human activity. If we are to stabilize the concentration of carbon dioxide in the atmosphere, we must reduce these carbon emissions to zero. This will take time, by most estimates 50 years for a full scale transition away from fossil fuels. In the meantime, we must reduce carbon emissions by 50% to stabilize atmospheric carbon dioxide concentrations, and we can do this through forest management.
According to the global carbon budget, between 2000 and 2010, the average yearly global emissions of carbon were about 9 billion metric tonnes (BMT), with 8 BMT from fossil fuels and 1 BMT from land management, largely from deforestation in the tropics. Of these total emissions, just less than half (about 4 BMT) remained in the atmosphere, while a quarter (2.4 BMT) each were taken up by the land and the ocean.
As the uptake by land and ocean is driven by the concentration in the atmosphere, not by the annual emissions, all we need to do for immediate stabilization is reduce emissions by the amount of carbon accumulating in the atmosphere each year (4 BMT). If we stopped deforestation and forest degradation completely, we would reduce emissions by 1 BMT/year. If we reforested an area half the size of the United States, we would reduce emissions by another 1 BMT/year. And if we allowed forests that are recovering from harvests and from agricultural abandonment to grow, we could reduce emissions by 1-3 BMT/year. Altogether, these three activities could lower carbon emissions by 4 BMT/year, enough to stabilize the carbon dioxide concentration for 40 to 50 years – but not much longer because grown forests remove less carbon from the atmosphere than young forests.
The scale of the problem and its solution is enormous. Such an undertaking would not be easy; it would require international agreement. Furthermore, the estimates above are what could happen. There are a number of serious caveats.
To begin with, the idea that we can stabilize the carbon dioxide concentration by managing forests is an interim strategy (a few decades). It buys the time the world needs to convert from fossil to renewable energy. It’s not a permanent solution. Emissions from fossil fuels must be eliminated during this interval.
The greatest impediment to managing forests at this scale is that harvests of timber, fuelwood, and biofuel would be prohibited and agricultural expansion limited. The real question is, will the threat of climatic disruption be great enough to change fundamental economics rendering a standing forest more valuable than other uses of that land?
The window of opportunity is closing. The longer we wait, the more difficult it will be to stabilize the concentration of carbon dioxide by forests alone. Fossil fuel emissions in 2013 were already nearly 25% greater than the average during 2000-2010. Unless we reverse the current trend, using forest management to transition to a fossil-fuel free Earth, we are headed for a warming of 7° F within the century.