Abstract: The cumulative effects of seasonal Earth processes in different places and times in the atmosphere, hydrosphere, and cryosphere essentially and inevitably shape global climate conditions. Therefore, the article investigates the possibilities for modelling the periodicity of the observable seasonal climate processes. The starting assumption of the study is that the seasonal climate processes are representable by two-phase linear periodic models based on observed data. A numerical algorithm elaborated in the sequel makes it possible to accumulate the seasonal effects of two successively progressive and regressive process phases of periodic climate changes in time. The model first tackles the reported seasonal growth of the atmospheric CO2 concentration. Next, it considers the observed seasonal cryospheric melting and freezing processes of the Antarctica and Greenland ice sheets and of the Arctic sea ice. It also elaborates on the reported seasonal sea level rise. Finally, the article summarises the interactions of periodic climate processes and the global climate conditions in time scale. The reports on global temperature rise are only on an annual basis. The article also emphasises the importance of control over the seasonal worsening and recovery scenarios for more appropriate projections of climate policies to 2100.