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Carbon cycle

While most of the Earth’s carbon can be found in the
geosphere, carbon is found in all living things, soils, the
ocean, and atmosphere
...
One
of the most important carbon compounds in the atmosphere
is carbon dioxide (CO2), while in rocks carbon is major
component of limestone, coal, oil and gas
...
By understanding how
human activities have altered the carbon cycle, we can
explain many of the climate and ecosystem changes we are
experiencing today, and why this rapid rate of change is
largely unprecedented in the Earth’s history
...
Click the image on the left to open the
Understanding the Global Change Infographics
...


What is the carbon cycle?

Carbon is transferred between the ocean, atmosphere, soil, and living
things over time scales of hours to centuries
...
As plants are eaten by herbivores and herbivores are eaten by
carnivores, carbon moves up the food web
...
When organisms die and decay carbon also returns to the
atmosphere or is integrated into the soil along with some of their waste
...


On longer timescales, significant amounts of carbon are transferred
between rocks and the ocean and atmosphere, typically over thousands to
millions of years
...
The resulting sediments, along with organic
material, can be transported (eroded) from the land to enter the ocean
where they sink to the bottom
...
These shells become buried
...
Over millions of years, these carbon-bearing rocks can be exposed to
sufficient heat and pressure to melt, causing them to release their carbon
back into the atmosphere as carbon dioxide via volcanism
...
Carbon from the
mantle (see plate tectonics) is also released into the atmosphere as
carbon dioxide through volcanic activity
...
Fossil fuels are derived from
the burial of photosynthetic organisms, including plants on land (which
primarily forms coal) and plankton in the oceans (which primarily forms oil
and natural gas)
...


Human activity, especially the burning of fossil fuels, has dramatically
increased the exchange of carbon from the ground back into the
atmosphere and oceans
...
Thus, the carbon dioxide
released from the burning of fossil fuels is accumulating in the atmosphere,
increasing average temperatures through the greenhouse effect, as well
as dissolving in the ocean, causing ocean acidification
...


The rate of exchange and the distribution of carbon in the Earth system is
affected by various human activities and environmental phenomena,
including:

● The burning of fossil fuels, which rapidly releases carbon dioxide
(CO2), a greenhouse gas into the atmosphere, increasing average
global temperatures and causing ocean acidification
...
For example, methane is
produced from the digestion of plant material by cows, and from the
bacteria that thrive in rice fields
...
The growing of crops
and the raising of livestock also affect local productivity and
biomass, and rates of photosynthesis, respiration, and decay of
organic material
...
When trees
grow they take carbon dioxide out of the atmosphere and transfer it
into their wood, leaves, bark, and roots
...

Thus, deforestation typically releases carbon dioxide, unless all the
material is used for construction, or for paper products
...
When temperatures
remain cold all year-round organic material decays very slowly, and it
remains in the soil
...
The increasing
temperatures also increase rates of decay, which further increases
the number of greenhouse gases in the atmosphere
...
For
example, the increased burial of dead plants and plankton decreases
decay thereby increasing the rate of formation of fossil fuels
...
For example, the
metamorphic reactions that occur under heat and pressure can
release carbon dioxide
...
Warming can increase these weathering reactions, but
not at a rate that can offset the increase in carbon dioxide due to
human activities
...


Earth system model about the carbon cycle
The Earth system model below includes some of the processes and
phenomena related to the carbon cycle
...
For example,
carbon is transferred among plants and animals over relatively short time
periods (hours-weeks), but the human extraction and burning of fossil
fuels have altered the carbon cycle over the decades
...
Can you think of additional cause and effect
relationships between the parts of the carbon cycle and other processes in
the Earth system?



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