The review recommended the prioritization of accounting principles that provide consistent consideration of natural disturbance regimes, temporal scales, and system boundaries. In contrast, an extensive study of the status and future potential of global bioenergy resources, systems and markets (SCOPE, 2015) suggested that as much as 30% of the world's fuel supply could be bio-based by 2050, although it also found that the implementation of successful bioenergy production systems will require clear sustainability metrics and monitoring programmes, stable land tenure, and effective local and national governance, conditions not yet established in many countries. This was an increase of 6.2 million hectares (1.4%) over the previous 12 months, although the increase was about 10 million hectares less than that seen in the preceding 12-month period. In the caseof the PEFC, data are reported to December 2014, and more forest may have been certified to May 2015. More than 80% of the double certification is in Europe (3.5 million hectares) and North America (2.6 million hectares).