![]() The loss of 140 Gt C in the terrestrial biosphere reflects the cumulative CO 2 emissions from land-use change (primarily slash and burn agriculture in the tropical rainforests), and is added to the 244 Gt C emitted by the burning of fossil fuels. Pre-industrial natural fluxes are shown in black, anthropogenic changes in red. Since the beginning of the industrial age, increasing amounts of additional carbon have entered the atmosphere annually in the form of carbon dioxide.Ģ.1 > The carbon cycle in the 1990s with the sizes of the various reservoirs (in gigatons of carbon, Gt C), as well as the annual fluxes between these. This transport presumably still occurs today at rates essentially unchanged. This is a result of the input of carbon from land plants carried by rivers to the ocean and, after decomposition by bacteria, released into the atmosphere as CO 2, as well as from inorganic carbon from the weathering of continental rocks such as limestones. It is assumed that, in this pre-industrial equilibrium state, the ocean released around 0.6 gigatons of carbon per year to the atmosphere. This relatively stable CO 2 concentration suggests that the pre-industrial carbon cycle was largely in equilibrium with the atmosphere. Today, we know that the CO 2 concentration in the atmosphere changed only slightly during the 12,000 years between the last ice age and the onset of the industrial revolution at the beginning of the 19th century. With respect to climate change, the greenhouse gas CO 2 is of primary interest in the global carbon cycle. ![]() In geological time that is quite fast, but from a human perspective it is too slow to extensively buffer climate change. Consequently, changes in atmospheric carbon content that are induced by the oceans also occur over a time frame of centuries. The carbon, however, requires centuries to penetrate into the deep ocean, because the mixing of the oceans is a rather slow (Chapter 1). The ocean is therefore the greatest of the carbon reservoirs, and essentially determines the atmospheric CO 2 content. At that time the carbon content of the atmosphere was only around 600 gigatons of carbon. The ocean, with around 38,000 gigatons (Gt) of carbon (1 gigaton = 1 billion tons), contains 16 times as much carbon as the terrestrial biosphere, that is all plant and the underlying soils on our planet, and around 60 times as much as the pre-industrial atmosphere, i.e., at a time before people began to drastically alter the atmospheric CO 2 content by the increased burning of coal, oil and gas. Today scientists can estimate fairly accurately how much carbon is stored in the individual reservoirs. But considering that carbon remains bound up in the rocks of the Earth’s crust for millions of years, then the exchange between the atmosphere, terrestrial biosphere and ocean carbon reservoirs could actually be described as relatively rapid. This process can occur over time spans of up to centuries, which at first glance appears quite slow. ![]() The three most important repositories within the context of anthropogenic climate change – atmosphere, terrestrial biosphere and ocean – are constantly exchanging carbon. the rocks on the planet, including limestones (calcium carbonate, CaCO 3). Even more carbon, however, is stored in the lithosphere, i.e. The oceans store much more carbon than the atmosphere and the terrestrial biosphere (plants and animals). Carbon can be stored in and exchanges between particulate and dissolved inorganic and organic forms and exchanged with the the atmosphere as CO 2. Carbon constantly changes its state through the metabolism of organisms and by natural chemical processes. Plants on land and algae in the ocean assimilate it in the form of carbon dioxide (CO 2) from the atmosphere or water, and transform it through photosynthesis into energy-rich molecules such as sugars and starches. The human body structure is based on it, and other animal and plant biomass such as leaves and wood consist predominantly of carbon (C). ![]()
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