The Large Scale Biosphere-Atmosphere Experiment in Amazonia (LBA) is an international research initiative led by Brazil to study the functioning of Amazonia as a regional entity with respect to the natural cycles of water, solar energy, trace-gases, carbon and nutrients, and how the physical, chemical and biological functioning of Amazonian ecosystems is altered due to land use and land cover and climate changes. The field phase of LBA started in 1998 and will end in 2004. It comprises over 100 studies covering an array of themes and land covers (forest, pasture, savanna, wetlands, agriculture, secondaty growth). LBA is also an experiment in capacity building and advanced training of students and young scientists from all Amazonian countries.

The physical climate component of LBA has revealed many new aspects of Amazonian climate. Contrary to expectations, clouds over western Amazonia resemble oceanic clouds during periods within the rainy season when the region is under the influence of the SACZ. Low aerosol content, relatively low cloud tops and infrequent lightning makes than quite diffetent in comparison to deep continental convective clouds and more similar to oceanic clouds. One LBA study revealed that the meso to large scale deforestation over western Amazonia may be related to an observed decrease of wet season rainfall. Natural and biomass burning aerosols have been the subject of a large number of studies. The hypothesis that heavy loadings of biomass burnig aerosols in the pre-rainy season may affect the preciptiation is being investigated thoroughly. LBA is also reducing the uncertainties on the carbon balance of Amazonian forests. Summing up a large number of studies (eddy correlation flux towers, forest inventories, inverse calculations, etc.), one can say that it appears that the undisturbed forest functions as a sink of carbon of 0.8 to 1.5 ton C.ha-1.yr-1. That has implications for the global carbon cycle. The surface water chemistry component of LBA has documented significant changes in streams draining deforested areas that could affetc aquatic life. The dynamics and impact of fire has been extensively studied in LBA for both forest and savanna (cerrado) ecosystems. In sum, LBA is putting forth a wealth of new knowledge about Amazonia that is key to the sustainable development of the region.