A globally comprehensive analysis of satellite and climate data between 1982–1999 was published in 2003. The results indicate an apparent greening of the biosphere. These changes could not have been identified without the up-to-date, consistent, and comprehensive picture of the planet that was provided by the long-term satellite data sets that are now available.
The results of this study demonstrate that net primary production (NPP), the amount of energy produced by plants through photosynthesis minus what they use in respiration, increased globally by about six per cent during the last two decades of the 20th century. Increasing temperatures, precipitation, carbon dioxide levels, and nitrogen deposition, changes in cloud cover and land use have all been implicated in the global greening, even though their relative roles remain unclear. In addition, advances in agriculture and successful implementation of a number of conservation programmes around the world may have contributed to the greening trend.
The study revealed that ecosystems in tropical zones and in the high latitudes of the Northern Hemisphere accounted for 80 per cent of the increase in global net primary production. Tropical rainforests in the Amazon contributed nearly 40 per cent of the global increase, attributed to a decline in cloud cover and the resulting increase in the sun’s energy that reached the surface. Changes in monsoon dynamics resulted in more rainfall in the 1990s that led to increased vegetation over the Indian sub-continent and the African Sahel.