According to the Australian Academy of
Large amounts of CO2 are continually transferred to and from the
atmosphere, which exchanges carbon with the oceans and vegetation
on land. Until around 200 years ago, these natural exchanges were
in rough balance, shown by the nearly constant concentrations of
atmospheric CO2 for most of the last two thousand years.
The importance of human-caused CO2 emissions is that they are
disturbing this balance, adding carbon to the atmosphere faster
than it can be removed by uptake by vegetation, the slow mixing of
CO2 into the deep oceans, or the even slower weathering processes
that control the carbon balance on geological timescales.
According to the NASA Earth
Carbon is the backbone of life on Earth. We are made of carbon,
we eat carbon, and our civilizations-our economies, our homes, our
means of transport-are built on carbon. We need carbon, but that
need is also entwined with one of the most serious problems facing
us today: global climate change.
Forged in the heart of aging stars, carbon is the fourth most
abundant element in the Universe. Most of Earth's carbon-about
65,500 billion metric tons-is stored in rocks. The rest is in the
ocean, atmosphere, plants, soil, and fossil fuels.
Carbon flows between each reservoir in an exchange called the
carbon cycle, which has slow and fast components. Any change in the
cycle that shifts carbon out of one reservoir puts more carbon in
the other reservoirs. Changes that put carbon gases into the
atmosphere result in warmer temperatures on Earth.
Over the long term, the carbon cycle seems to maintain a balance
that prevents all of Earth's carbon from entering the atmosphere
(as is the case on Venus) or from being stored entirely in rocks.
This balance helps keep Earth's temperature relatively stable, like
This thermostat works over a few hundred thousand years, as part
of the slow carbon cycle. This means that for shorter time
periods-tens to a hundred thousand years-the temperature of Earth
can vary. And, in fact, Earth swings between ice ages and warmer
interglacial periods on these time scales. Parts of the carbon
cycle may even amplify these short-term temperature
On very long time scales (millions to tens of millions of
years), the movement of tectonic plates and changes in the rate at
which carbon seeps from the Earth's interior may change the
temperature on the thermostat. Earth has undergone such a change
over the last 50 million years, from the extremely warm climates of
the Cretaceous (roughly 145 to 65 million years ago) to the glacial
climates of the Pleistocene (roughly 1.8 million to 11,500 years