Global carbon cycle - How much CO2 remains in the atmosphere each year? and how much time do we have left? The exchange of carbon between the surface reservoirs of atmosphere, land and ocean on the one hand and the deep geological reservoirs on the other has been considerably accelerated by human use of fossil fuels. The result is a warming of the global climate at a rate unprecedent in Earth's history over the past 50 million years. Whether anthropogenic climate change can be halted in time is uncertain. This also depends on the feedback processes between the carbon cycle and climate changes.