This document contains the presentation on the role of cloud-aerosol interactions in climate change by G. Pandithurai, IITM, Pune at National climate research conference, IIT Delhi, March 5-6, 2010. Aerosol indirect effects (AIE) are generally referred to any aerosol induced modification of cloud microphysical properties (first AIE), cloud life time (second AIE), precipitation etc. All these effects are based on examining relative changes in cloud droplet size by aerosol. Twomey hypothesized that cloud droplet size decreases with increase in aerosols for a fixed liquid water content, which has been supported with several studies from ground and in situ observations and satellite data. A wide variation is noted for the sensitivity of cloud microphysics to aerosol and some of the differences were attributed to the different observational / analysis methods and natural variation. Extensive aircraft measurements were carried out over Indian subcontinent to document the aerosol and cloud microphysical properties under Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) during May-September 2009. During the CAIPEEX campaign (http://www.tropmet.res.in/~caipeex), the instrumented aircraft measurements were conducted to explore aerosol-cloud relationship over pre-monsoon and active monsoon conditions over India. To investigate the effect of aerosols on cloud droplet effective radius, simultaneous measurements of aerosol-CCN concentration, cloud droplet effective radius and liquid water content (LWC) are analyzed. Giant CCNs can reduce the number of cloud droplets under polluted conditions by suppressing the supersaturation reached in a cloud base. The reduced droplet number concentration together with presence of giant CCNs could lead to increased cloud droplet effective radius. Sensitivity of aerosol on cloud microphysics, effect of entrainment mixing and updraft will be presented. Aircraft measurements are of expensive proposition and have several limitations such air traffic control. Alternately, high altitude sites experience clouds close to ground and can be monitored for long-term under different environmental conditions. Hence, it is proposed to establish a mountain top observatory at Mahabaleshwar under climate change scheme.