Many are from the late 1960s to present or early 1970s to present.
Recent statistics cover the last decade.
The information presented in the Environmental Data Report series is compiled from a variety of sources. Data from the international monitoring programs of GEMS and associated organizations are also used. The assessment of environmental trends, both temporally and spatially, is often hampered by a lack of comparable data at regional and global scales. National data cannot always be integrated readily into regional or international datasets because of lack of agreement on analytical measurement procedures or definition of descriptive criteria or variations in frequency of measurements or data collection. Despite the wealth of data, particularly from developed countries, reliable data on some major problems, such as rates of deforestation, land degradation, and toxic waste dumping, are still lacking.