Fig. 3: Estimated annual average carbon costs (Gt CO₂e yr⁻¹) of future global wood harvests between 2010 and 2050.

Estimates of the average, annual, time-discounted carbon costs of global wood harvests under different scenarios of future wood supply. All scenarios (described in Table 1) assume the same future consumption except scenario 7, which cuts wood fuel use in half in 2050 from projected levels. Estimates of 3.6–4.2 Gt CO₂e yr⁻¹ apply a 4% discount rate to changes in carbon storage for 40 years after each year’s wood harvest. These account for forest regrowth and other changes in carbon storage pools over time but discount the value of those changes back to the year of harvest. They therefore represent harvest-year equivalent emissions—that is, the value of net changes in carbon each year if all occurred in the year of harvest (Extended Data Fig. 4 shows modest effects of varying discount rates from 2 to 6% or discounting over 100 years). Dark green regions represent emissions at 2010 wood supply levels, with light green representing emissions to meet  ‘additional business as usual (BAU) demand’. Blue represents estimated ‘substitution benefits’, which are estimated reductions in fossil fuel and other production emissions when using wood to replace concrete and steel in construction or as wood fuel to replace propane gas. Substitution benefits do not mean that wood use has climate benefits overall because they do not account for lost carbon storage—that is, biogenic emissions. Just as a small car still releases emissions even if less so than a large car, substitution benefits do not alter absolute emissions from wood harvest. Source: CHARM.