FAO is the Food and Agriculture Organization of the United Nations. The discussed report (FAO: Global Forest Assessment 2010) led to underestimation of the anthropogenic CO2 emissions from land use change (LUC) since 2000. Additionally, China (and possibly some other countries) has underreported its emissions from fossil fuels use. Thus, worldwide CO2 emissions in the last 10-15 years have been underestimated by 8-15%. The sky has not fallen, but the implications for the physical models of the carbon cycle are severe. The actual amount of CO2 naturally removed from atmosphere since 2000 has been 15-30% higher than what the official data (available for AR5 and through the end of 2014) indicated. All carbon cycle models that agree with the official data are wrong.

Despite being issued by a United Nations organizations, FAO-FRA 2010 honestly warns that it contains inaccurate data and cannot be used for scientific purposes. A couple examples:

At the global level, the area of other wooded land decreased by about 3.1 million hectares per year during the decade 1990 to 2000 and by about 1.9 million hectares per year in the last decade (2000–2010). This finding should be treated with caution, however, because many countries still do not have compatible information over time for other wooded land, and thus one estimate was frequently used as the best available figure for all four reporting years. (pp. 20-21, my emphasis)

Indonesia, for instance, reported a significant increase in the area of mangroves between 1990 and 2000. Australia reported a similar increase during the period 2005 to 2010 after an even bigger decrease from 2000 to 2005. The reported figures therefore warrant further analysis and the results above should be treated with caution. (pp. 29-30, my emphasis)

The report repeats the word “caution” ten times.

Theoretically, satellite imagery is available to FAO to verify the national reports, but nothing in the report indicates that such verification has been performed. Satellite imagery requires manual interpretation, and the interpretations were performed selectively and with many limitations. Even more suspicious is this passage:

FAO used an interdependent, manual interpretation of satellite scenes at a scale of 1:250,000, conducted by local professionals, where possible, and internationally experienced professionals in other areas. (p. 337, my emphasis)

Simply put, if the local professionals are incompetent and/or influenced by local governments, then the results are neither reliable nor independent. This quote refers to 1990, but there is no reason to think that this aspect of the methodology has improved since then.

More reliable satellite data for tropical deforestation by burning indicates an increase (rather than decrease) in the deforestation rate, and strong correlations with the global economic cycle. See Fig. 2 in R. A. Houghton, J. I. House, J. Pongratz, G. R. van der Werf, R. S. DeFries, M. C. Hansen, C. Le Quere, and N. Ramankutty, “Carbon emissions from land use and land-cover change.”