The presentation will focus on scientific issues of importance to global change and climate change research: interactions of reactive trace and greenhouse gases between the biosphere and atmosphere in combination with boundary layer processes, importance of land use and land cover for climate studies, and aerosol-cloud-precipitation-climate interactions. These issues are of vital importance and research is carried out under the auspices of the multi- and cross-disciplinary Integrated Land Ecosystem-Atmosphere 81 Processes Study (iLEAPS), a core project of the International Geosphere- Biosphere Programme (IGBP) in collaboration with other international research organizations. The interactions between the biosphere and the atmosphere mediated by the production and emission of reactive trace gases are crucial and central components of the study of the Earth system and life science. Their importance to the structure and functioning of terrestrial ecosystems and to chemical weather of Earth is only now beginning to be appreciated, and there is wide acknowledgement that these are areas needing concerted scientific effort on a large scale. The current knowledge of the relation between physical and chemical processes and their impact on the larger spatial and temporal scale distribution of atmospheric compounds requires combination of knowledge of sources and sinks of atmospheric compounds, boundary layer processes: mixing, dispersion and exchange with free troposphere. This requires implementation of surface and boundary layer models in air quality and atmospheric chemistry-transport models. Recent studies suggest that the increased aerosol loading may have changed the energy balance in the atmosphere and at the Earth’s surface and altered the global water cycle in ways that make the climate system more prone to precipitation extremes. As yet, we do not fully understand how the aerosol affects the development of precipitation, nor the extent to which it affects the cycles of water and radiant energy in the climate system as a whole. Achieving better understanding on the scientific issues briefly described above is not only a major scientific challenge, but is also important to policy makers and stakeholders for making decisions on adaptation and mitigation strategies.