CO2 capture and geological storage (CCS) should be implemented in Poland, if combustion of coal will remain as a main source of energy in Poland, and European Union climate policy requirements are to be met. Despite existing experience and number of existing operational projects worldwide, a common fear concerning safety of the onshore, large scale geological storage of CO2 still occurs. Because of that fear, some European countries substantially limited even demonstration CCS projects. However, opinions on the method's safety should be based on solid geological evidence, not fears. Herein I provide some evidence from the Lower Jurassic basin in Poland that the method is safe. The key issue is the geological integrity of a seal. High-resolution sequence stratigraphy verified by chemostratigraphical correlation based on 13C isotope correlation, proved that one of key seal formations, the lower Toarcian Ciechocinek formation composed of clayey-muddy rocks with sandstone intercalation, is integral in terms of its lithology and spatial extent over the larger part of the Polish basin and provides an excellent seal. Origin of such favourable properties is attributed to climatic conditions (supergreenhouse conditions on land) during the Toarcian Oceanic Anoxic Event and high sea level at that time. Moreover, similar conditions occurred for four times during the Early–Middle Jurassic times, creating another over-regional seal formations in the large parts of the Polish Mesozoic epicontinental basin. It can allow a tiered sequestration method, using several sequestrartion systems (reservoir-seal couples) one above another, thus allowing much more voluminous and effective storage of CO2 and methane (for economic purposes) in selected structures.