Ecologists and atmospheric scientists are concerned with understanding how biospheric characteristics of the land surface will be modified in response to changing climate and CO2 over the next 50 to 100 years. Ecosystem properties (e.g., canopy structure and N content, photosynthetic rate, decomposition rates, plant physiognomy) control fluxes of energy, water, and trace gases between the land surface and the atmosphere. Modeling of these properties using satellite inputs will require better understanding of how plant physiology and chemistry reflect the balance between above-and belowground limiting factors. High spectral resolution spaceborne spectrometers may estimate canopy N, lignin or other constituents that affect decomposition rates. These measurements, in combination with estimates of light interception, should allow model simulations of above-and belowground ecosystem properties. In addition, community dynamics that affect ecosystem properties need to be incorporated into the modeling framework so that the coupling of abiotic impacts on short time scales to biotic changes over longer time scales can be appropriately assessed. The biospheric sensitivity to climatic variations in arid and semiarid lands provide a unique environment to study land-atmosphere interactions. These regions occupy approximately one-third of the Earth's land area evenly distributed between temperate and tropical latitudes. These regions may be among the earliest systems to exhibit the effects of climatic change because these systems processes in these are tightly coupled to rainfall.