Because productivity in the ocean is often limited by the availability of certain nutrients, it has been hypothesized that ocean fertilization could stimulate plankton blooms and thus enhance the transfer of CO2 from the atmosphere to the oceans. For example, in some parts of the ocean, productivity is limited by the availability of iron, which suggests the potential for increasing carbon uptake via iron fertilization. Experiments to test this hypothesis have so far resulted in considerable uncertainty about its potential. While this approach could store some carbon, the maximum achievable rates might be only a small fraction of the total carbon emitted by human activities.
On land, changes in land use and land cover by human actions have been responsible, over time, for as much as 35 percent of human-induced CO2 emissions. Today, emissions from tropical deforestation and other changes in land use account for around 17 percent of annual CO2 emissions. Land management practices that reduce deforestation and degradation, or that enhance storage of carbon in land ecosystems, could provide potentially low-cost options to reduce GHG concentrations in the atmosphere and thus limit the magnitude of future climate change. Changes in land use can also influence temperatures by changing the reflective properties of the Earth's surface and by altering rates of transpiration of water. The overall potential to limit climate change through management of land and ocean ecosystems has not been thoroughly evaluated, however.
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