CARBON CYCLE

The carbon cycle is the circulation and transformation of carbon back and forth between living things and the environment. Carbon compounds are present in living things like plants and animals and in nonliving things like rocks and soil.

The amount of carbon on the earth and in Earth's atmosphere is fixed, but that fixed amount of carbon is dynamic, always changing into different carbon compounds and moving between living and nonliving things.

Carbon is released to the atmosphere from what are called "carbon sources" and stored in plants, animals, rocks, and water in what are called "carbon sinks."

There are many carbon sources like these;
Plants.
Through photosynthesis plants take carbon dioxide out of the atmosphere and release oxygen.The carbon dioxide is converted into carbon compounds that make up the body of the plant, which are stored in both the parts of the plants like shoots, leaves and roots.

Animals.
Animals eat the plants, breath in the oxygen, and exhale carbon dioxide. The carbon dioxide created by animals is then available for plants to use in photosynthesis. Carbon stored in plants that are not eaten by animals eventually decomposes after the plants die, and is either released into the atmosphere or stored in the soil.

Geologic processes.
Large quantities of carbon can be released to the atmosphere through geologic processes like volcanic eruptions and other natural changes that destabilize carbon sinks. For example, increasing temperatures can cause carbon dioxide to be released from the ocean.

While a portion of the total amount of carbon present on the earth runs through the carbon cycle relatively quickly, another portion of the carbon is caught up in long-lived and stable carbon sinks.

In Earth’s past, the carbon cycle has changed in response to climate change. Variations in Earth’s orbit alter the amount of energy Earth receives from the Sun and leads to a cycle of ice ages and warm periods like Earth’s current climate. Today, changes in the carbon cycle are happening because of people. We perturb the carbon cycle by burning fossil fuels and clearing land. By burning coal, oil, and natural gas, we accelerate the process, releasing vast amounts of carbon (carbon that took millions of years to accumulate) into the atmosphere every year.

Today we can obtain the data of amount of emissions from the World Bank web site. (http://data.worldbank.org/indicator/EN.ATM.CO2E.PC/countries/CN-GB-US-ES?display=graph)

CO2 emissions (kt)

 

CO2 emissions (metric tons per capita)

These graphics show that China is the the largest producer of CO2 and USA is the greatest producer per capita. However, we can observe that the amount of emissions per capita in some counties have steadily declined since 2007, excepting China.

Since the beginning of the Industrial Revolution, when people first started burning fossil fuels, carbon dioxide concentrations in the atmosphere have risen from about 280 parts per million to 387 parts per million.
 
Nowadays human activity has contributed to an atmospheric concentration of carbon dioxide not seen since the Pliocene epoch between 2.6 and 5.3 million years ago.

Sources:
http://www.esrl.noaa.gov/gmd/ccgg/trends/#mlo_full
http://earthobservatory.nasa.gov/Features/CarbonCycle/