摘要：Global climate policy initiatives are now being proposed to compensate tropical forest
nations for reducing carbon emissions from deforestation and forest degradation (REDD).
These proposals have the potential to include developing countries more actively in
international greenhouse gas mitigation and to address a substantial share of the world's
emissions which come from tropical deforestation. For such a policy to be viable it must
have a credible benchmark against which emissions reduction can be calculated. This
benchmark, sometimes termed a baseline or reference emissions scenario, can be based
directly on historical emissions or can use historical emissions as input for business as usual
projections. Here, we review existing data and methods that could be used to measure
historical deforestation and forest degradation reference scenarios including FAO (Food and
Agricultural Organization of the United Nations) national statistics and various remote
sensing sources. The freely available and corrected global Landsat imagery for 1990,
2000 and soon to come for 2005 may be the best primary data source for most
developing countries with other coarser resolution high frequency or radar data as a
valuable complement for addressing problems with cloud cover and for distinguishing
larger scale degradation. While sampling of imagery has been effectively useful
for pan-tropical and continental estimates of deforestation, wall-to-wall (or full
coverage) allows more detailed assessments for measuring national-level reference
emissions. It is possible to measure historical deforestation with sufficient certainty
for determining reference emissions, but there must be continued calls at the
international level for making high-resolution imagery available, and for financial and
technical assistance to help countries determine credible reference scenarios. The
data available for past years may not be sufficient for assessing all forms of forest
degradation, but new data sources will have greater potential in 2007 and after.
This paper focuses only on the methods for measuring changes in forest area,
but this information must be coupled with estimates of change in forest carbon
stocks in order to quantify emissions from deforestation and forest degradation.
