Feedback in carbon cycle

• The global carbon cycle is currently in a state of disequilibrium. Human activity, primarily through burning fossil fuels, has increased the concentration of CO2 in the atmosphere, the acidity of the oceans and the flux of carbon between the major stores
• Within the carbon cycle there are feedback loops which could either restore equilibrium or induce further disequilibrium
• Negative feedback could neutralise rising levels of atmospheric CO2 by stimulating photosynthesis. This process is called carbon fertilisation. In this way excess CO2 is extracted from the atmosphere and stored in the biosphere. Eventually much of this carbon would find its way into long-term storage in soils and ocean sediments, allowing the system to return to a steady state
• However, increased primary production through carbon fertilisation is conditional on the availability of other requirements for photosynthesis such as sunlight, soil nutrients, nitrogen and water. So, although there is evidence that primary production has indeed increased in recent years it is not possible to say with certainty that this is due to increased atmospheric CO2
• For instance, recently significant increases in primary production have been observed in the Amazon rainforest but this could be explained by lower rainfall, with less cloud cover and more sunlight rather than an increase in CO2
• Positive feedback could tip the carbon cycle into greater disequilibrium. For instance, global warming will intensify the carbon cycle, speed up decomposition and release more CO2 to the atmosphere, thus amplifying the greenhouse effect
• Another positive feedback effect is seen in Artic tundra where global warming is occurring faster than in any other region (1.5*-2.5* in the past 30 years). As the Arctic sea ice and snow cover shrinks, large expanses of sea and land are exposed. This means that more sunlight is absorbed, warming the tundra and melting the permafrost. This is significant for the global carbon cycle because the tundra stores an estimated 1600 GT of organic carbon in the permafrost