Human activity has released carbon from sequestration in long-term reservoirs. Human activities accelerate the uxes of material from one reservoir to another in biogeochemical cycles. Burning fossil fuels transfers co2 from lithospheric reservoirs into the atmosphere. Deforestation transfers co2 from terrestrials into the atmosphere. Methane ch4 from fossil fuel deposits, livestock, land lls, and crops such as rice. Nitrous oxide n2o from feedlots, chemical manufacturing plants, auto emissions, and synthetic nitrogen fertilizers. Water vapor = the most abundant greenhouse gas and contributes most to the greenhouse effect. There are many feedback cycles in the climate system. Adding carbon dioxide to the atmosphere tends to warm the atmosphere causing global warming. Since water vapor is a greenhouse gas, the atmosphere tends to warm even more as water vapor increases. Adding carbon dioxide to the atmosphere tends to warm the atmosphere, causing global warming. The warm atmosphere causes surface water to evaporate and become water vapor.