The carbon cycle describes the movement of carbon through the biosphere, geosphere, hydrosphere and atmosphere. Carbon is exchanged through processes like photosynthesis, respiration, and the weathering of rocks. Recently, the carbon cycle has become imbalanced due to human activities like burning fossil fuels and deforestation, which emit carbon dioxide into the atmosphere faster than natural processes can reabsorb it. The excess carbon dioxide is causing global warming and has negative effects on plants, humans and the climate.

1. CARBON CYCLE

2. CONTENTS
• Introduction
• Carbon Cycle
• Procedure
Photosynthesis
Respiration
Weathering of rocks
Auto and factory emissons
• Imbalance of Carbon Cycle
• Effect of excess CO2 on plants
• Effect of excess CO2 on humans
• Effect of excess CO2 on global warming

3. CARBON CYCLE
The carbon cycle is the biogeochemical cycle by which carbon is
exchanged among the biosphere,
pedosphere, geosphere, hydrosphere, and atmosphere of the
Earth.
Along with the nitrogen cycle and the water cycle, the carbon
cycle comprises a sequence of events that are key to making
the Earth capable of sustaining life; it describes the movement
of carbon as it is recycled and reused throughout the biosphere.

6. GLOBAL CARBON BUDGET
The global carbon budget is the balance of the
exchanges (incomes and losses) of carbon between
the carbon reservoirs or between one specific loop
(e.g., atmosphere ↔ biosphere) of the carbon cycle.
An examination of the carbon budget of a pool or
reservoir can provide information about
whether the pool or reservoir is functioning as a
source or sink for carbon dioxide.

7. PROCEDURE
Plants use carbon dioxide and sunlight to make their own food
and grow. The carbon becomes part of the plant. Plants that die
and are buried may turn into fossil fuels made of carbon like coal
and oil over millions of years. When humans burn fossil fuels,
most of the carbon quickly enters the atmosphere as carbon
dioxide.
Photosynthesis:
Plants and photosynthetic algae and bacteria use energy from
sunlight to combine carbon dioxide (C02) from the atmosphere
with water (H2O) to form carbohydrates. These carbohydrates
store energy. Oxygen (O2) is a byproduct that is released into the
atmosphere. This process is known as photosynthesis.
carbon dioxide + water + sunlight -> carbohydrate +
oxygenCO2 + H2O + sunlight -> CH2O + O2

8. Respiration:
Plants (and photosynthetic algae and bacteria) then use some of
the stored carbohydrates as an energy source to carry out their
life functions. Some of the carbohydrates remain as biomass (the
bulk of the plant, etc.). Consumers such as animals, fungi, and
bacteria get their energy from this excess biomass either while
living or dead and decaying. Oxygen from the atmosphere is
combined with carbohydrates to liberate the stored energy.
Water and carbon dioxide are byproducts.
oxygen + carbohydrate -> energy + water + carbohydrateO2 +
CH2O -> energy + H2O + CO2

9. Weathering:
•Carbon dioxide and the other atmospheric gases dissolve in
surface waters. Dissolved gases are in equilibrium with the gas in
the atmosphere.
•Carbon dioxide reacts with water in solution to form the weak
acid, carbonic acid. Carbonic acid disassociates into hydrogen
ions and bicarbonate ions. The hydrogen ions and water react
with most common minerals (silicates and carbonates) altering
the minerals.
•The products of weathering are predominantly clays (a
group of silicate minerals) and soluble ions such as calcium,
iron, sodium, and potassium. Bicarbonate ions also remain in
solution; a remnant of the carbonic acid that was used to weather
the rocks.

10. Auto and factory emissions:
•Aside from these natural processes, carbon dioxide is also emitted through
the combustion or burning of fossil fuels such as coal, oil, and natural gas.
•Combustion occurs when vehicles are driven as well as when power plants
and industrial plants are utilized. Combustion, otherwise known as burning,
is the greatest source of carbon dioxide emissions globally.
• Typically, fossil fuels are burnt for electricity generation in homes and
buildings, industrial uses, as well as transportation.
•Petroleum is the largest share of domestic energy demands. Second is
coal, followed by natural gas (EPA, 2006).
• Electricity generation is the largest problem in relation to using
petroleum as fuel, rivaled followed closely by industrial processes that use
petroleum as fuel as well.

11. Image Credit: http://www.pbs.org/wgbh/pages/frontline/heat/art/graph3.jpg

12. IMBALANCE IN CARBON CYCLE
•In addition to the carbon dioxide emissions that result from industrial
processes, deforestation is a serious environmental threat in terms of carbon
dioxide emissions.
•Carbon is naturally removed from the atmosphere to be stored in oceans and
the soil surrounding the roots of many plants. Areas where carbon is
stored are otherwise known as carbon “sinks.”
• Forested areas are large carbon sinks because enormous amounts of
carbon dioxide are naturally stored in the soil, a result of
photosynthesis. Because of this, logging is not encouraged as an eco-friendly
practice, whether a small number of trees are cut down or a large number.

13. •When a large group of trees is removed at once, either deliberately by logging or
accidently in a forest fire, it is titled as deforestation. When this occurs, carbon
dioxide is released from the soil at rates that are damaging to the
environment because there are no longer any trees to contain the carbon dioxide.
•Technically defined as the “permanent removal of standing forests,” by the EPA,
following the destruction of a forest, typically, a large number of trees are not
planted.
•This lack of growth throws off the equilibrium of the environment, causing massive
CO2 emissions though no photosynthesis is occurring in order to utilize the carbon
dioxide or trees to store it, thus making deforestation extremely problematic.
•Normally, forested areas are not precarious because the decomposition that occurs
naturally results in the slow release of carbon dioxide. However, in the case of a
forest fire or mass logging, carbon dioxide is released at an alarmingly high
rate, contributing significantly to the greenhouse effect with the
increase. Overall, deforestation is a large contributor to carbon dioxide emissions
globally.

14. This photo depicts a forest fire in Afghanistan, which has lost over 70% of its’
forests due to deforestation.

15. Effect of CO2 increase on plants
•Elevated CO2 leads to changes in the chemical composition of plant tissues.
•Due to increased photosynthetic activity, leaf nonstructural
carbohydrates (sugars and starches) per unit leaf area increase on
average by 30–40% under FACE elevated CO2 (Ainsworth 2008; Ainsworth &
Long 2005).
•Leaf nitrogen concentrations in plant tissues typically decrease in FACE
under elevated CO2, with nitrogen per unit leaf mass decreasing on average by
13% (Ainsworth & Long 2005).
•This decrease in tissue nitrogen is likely due to several factors: dilution of
nitrogen from increased carbohydrate concentrations; decreased uptake of
minerals from the soil, as stomatal conductance decreases and plants
take up less water (Taub & Wang 2008); and decreases in the rate of
assimilation of nitrate into organic compounds (Bloom et al. 2010).

16. Effect of CO2 increase on
humans
•Carbon dioxide is a toxic gas which is odourless and colourless.
Rising levels of carbon dioxide affect the human body.
•Hypercapnia , is a condition where there is too much carbon
dioxide (CO2) in the blood. Carbon dioxide is a gaseous product of
the body's metabolism and is normally expelled through
the lungs.
•Hypercapnia normally triggers a reflex which increases
breathing and access to oxygen, such as arousal and turning
the head during sleep. A failure of this reflex can be fatal, as
in sudden infant death syndrome.

17. Contribution of CO2 in Global
Warming
•Carbon dioxide doesn't absorb the energy from the sun i.e.<4000 nm, but it does
absorb some of the heat energy released from the earth i.e. >4000 nm.
•So this leads to Green house effect , carbon dioxide lets the light energy in, but
doesn't let all of the heat energy out, similar to a greenhouse.
•Currently, the amount of carbon dioxide in the atmosphere is increasing at the rate
of about one part per million per year.
•If this continues, some meteorologists expect that the average temperature of
the earth will increase by about 2.5 degrees Celsius. This doesn't sound like
much, but it could be enough to cause glaciers to melt, which would cause coastal
flooding.