Increased carbon sink in temperate and boreal forests

An intense search is under way to identify the 'missing sink' in the world carbon budget of perhaps 2 Pg year(-1) (petagrams, or billion tonnes) of carbon, but its location and mechanism have proved elusive. Here we use a new forest inventory data set to estimate the carbon sink and the carbon pool of woody biomass in 55 countries that account for nearly all temperate or boreal forests and approximately half the world's total forest area. In each country there was a net accumulation of biomass; together, the carbon sink of woody biomass was 0.88 Pg year(-1) during the 1990s with estimated uncertainty from 0.71 to 1.1 Pg year(-1). This estimate, already about half of the missing sink, would probably be even larger if carbon accumulation in soil and detritus were also accounted for, but we are unable to quantify that additional sink. The sink is twice that estimated for the woody biomass of these forests a decade ago due to higher estimates for tree growth throughout the region and decreased timber harvests in Russia. In contrast, the new data indicate a carbon pool that is smaller than earlier estimates because of improved data for Russia and Australia.