We observed CO2 hydrate decomposition and reformation (re-growth) through temperature and pressure changes using a microscope. At pressures above CO2 vapor-liquid equilibrium P-s, decomposition from increasing temperatures left small liquid CO2 drops in the solution phase. Conversely, below P-s, decomposition from increasing temperatures was more rapid due to the release of CO2 gas that mechanically broke the hydrate apart. Similarly, hydrate decomposition by a pressure decrease also released CO2 gas that broke the hydrate apart. Reformation occurred more readily only by cooling, not by a pressure increase. A barrier to CO2 nucleation can explain this memory effect by allowing a greater concentration of CO2 to be left in the aqueous solution after hydrate decomposition.