Thermal decomposition reactions usually occur at very high temperatures. In these reactions one compound is heated, for example, copper carbonate and it breaks down to produce two or more substances.

These carbonates do not exchange with the atmosphere ... (C) In the coastal ocean, photosynthesis, decomposition and re-exchanging of CO2 with the atmosphere still continue. Solid organic carbon ...

To make concrete, limestone, or calcium carbonate, is mixed with clay and other materials and then calcined at high temperatures, so CO2 is released via the thermal decomposition of calcium carbonate.