An introduction to climate change - Climate Change: Biological and Human Aspects - page 19

1. Global budgets based on atmospheric data and models. These use data from nearly
100 sites around the Earth of atmospheric carbon dioxide and isotopes.
2. Global budgets based on models of oceanic carbon uptake. These use models of
oceanic carbon cycle and chemistry linked to those of terrestrial and atmospheric
sources.
3. Regional carbon budgets from forest inventories. Many developed nations have
national forest inventories and changes in volumes over time can indicate sources
or sinks of carbon. However, we are a long way from making this accurate, either
on a national basis or for global coverage, although progress is being made.
4. Direct measurements of carbon dioxide above ecosystems. Using stand towers
in forests it is possible to measure changes in carbon dioxide being given off or
absorbed. (This is quite different from measuring atmospheric carbon dioxide on
top of an Hawaiian volcano - one of the key measurement sites - combined with
scores of other direct atmospheric measurements to obtain a hemispheric average.)
5. Earth system science modelling using ecosystem physiology with global models
built up from global biome and ecosystem data. One of the big questions here
(apart from the accuracy of the size of the ecosystem components) is whether all
the important ecosystem processes have been included or properly quantified.
6. Carbon models based on changes in land use. This is related to item 5 and has
similar constraints.
Having looked at the broad areas of research into the carbon cycle, this leads
us on to the question of whether, because we are already altering one part of the
carbon cycle so as to increase atmospheric carbon dioxide, we can alter another part
to counteract this effect. Given that carbon dioxide is the principal anthropogenic
greenhouse gas, and that the carbon cycle is the determining phenomenon in its
atmospheric concentration, it would at least appear logical that we might alter the
way carbon is currently cycled so as to offset atmospheric carbon increases. One way
would be to increase terrestrial photosynthesis through planting new forests, thus
sequestering carbon, and we will return to forests and biofuel options later (see the
end of Chapter 7 and also some additional thoughts in Appendix 4). Another might
be to increase marine photosynthesis.
Marine photosynthesis is mainly carried out by phytoplankton in the open oceans.
The dominant species in the sea are the prokaryotes (organisms without internal
structures surrounded by cell membranes) Prochlorococcus and Synechococcus .Both
are cyanobacteria (also known as blue-green algae). In terms of crude numbers,
Prochlorococcus is probably the most populous species on the planet. In addition
to sunlight, carbon dioxide and water, these plankton species also require nitrates,
phosphates and small amounts of metals. In the ocean, close to the surface, more
than enough sunlight is present to drive photosynthesis, but it has been found (in
parts of the Pacific Ocean at least) that raising the concentration of iron to about
4 nM (nanomoles per litre) results in planktonic blooms and associated increased
photosynthetic production. The most dramatic of these experiments were the IronEx
I (1993) and II (1996) experiments that covered an area of about 70 km 2 , although
an area larger than this (1000 km 2 ) had to be surveyed due to the blooms' drift.