In order to answer these questions, and to test the validity of the hypothesis, a number of processes must be understood and modeled with sufficient fidelity. These are discussed in section III. 2. It should be noted that this theme couples with and strongly complements the preceding theme. The strongest link is the common need for improved models of the mean and variable distribution of water vapor, its transport and convergence, and the distributions of evaporation and precipitation. In this regard, the primary distinction between the two themes is with respect to the time scale of interest, but given the strong nonlinearities associated with deep convection and precipitation, the linkage of these two themes is quite real.
Climate variability appears to be sensitive to the mean state of the climate system.
For example, simulations of the earth's climate under doubled CO2 suggest that the monsoon and interannual variations are influenced by the increase in the mean temperature of the tropics, however the predicted effects are model-dependent. It is reasonable to expect that other aspects of short term climate variability may be affected by long-term natural climate changes or by anthropogenic forcing of the atmosphere. Aerosols in the lower troposphere are suggested to have reduced the global warming expected from current levels of anthropogenic CO2, so their concentration and distribution are important. The sources of anthropogenic aerosols include fossil fuels and industrial processes, as well as biomass burning. Natural sources include the ocean surface, desert dust, and volcanic eruptions.