The subject of this paper is to analyse the climate change and its influence on the energy performance of building and indoor temperatures. The research was made on the example of the city of Kielce, Poland. It was was carried out basing on the Municipal Adaptive Plan for the city of Kielce and climate data from the Ministry of Investment and Development.The predicted, future parameters of the climate were estimated using the tool Weather Shift for Representative Concentration Pathways (RCP). The analysis took into consideration the RCP4.5 and RCP8.5 scenarios for years 2035 and 2065, representing different greenhouse gas concentration trajectories. Scenario RCP4.5represents possible, additional radiative forcing of 4.5 W/m2 in 2100, and RCP8.5 an additional 8.5 W/m2. The calculated parameters included average month values of temperature and relative humidity of outdoor air, wind velocity and solar radiation. The results confirmed the increase of outdoor temperature in the following year. The values of relative humidity do not change significantly for the winter months, while in the summer months decrease is visible. No major changes were spotted in the level of solar radiation or wind speed. Based on the calculated parameters dynamic building modelling was carried out using the TRNSYS software. The methodology and results of the calculations will be presented in the second part of the paper.