weather parameters mainly temperature and rainfall
at least 40 years average temperature and rainfall data need to find climate change. if the region is cold region ice balance also calculate to find the albedo range is easy to find the temperature change
Rainfall and temperature are the major parameters shall be considered to study the climate change over a regions. The change in pattern of rainfall intensity and distribution also could be analyzed.
As Sandeep Vm say above. Also realize that is the root to understanding the physical or natural impact - don't forget about the societal / human impact including economic, infrastructure, and livelihood aspects.