Climate change feedback

Matear R. J. and Hirst A. C. (1999) Climate change feedback on the future oceanic CO2 uptake. Tellus 51B, 722-733. 

Between the emission of greenhouse gases and change in the climate are a range of climate and biological cycles that can influence the end result. Such outcome-modifier effects are called feedbacks or indirect effects in the climate change literature. 

Feedbacks may be affected directly by atmospheric CO2, as in the case of possible CO2 fertilization of terrestrial production, or indirectly through the effects of atmospheric CO2 on climate. Furthermore, feedbacks between the carbon cycle and other anthropogenically altered biogeochemical cycles (e.g., nitrogen, phosphorus, and sulfur) may affect atmospheric CO2. If the creation or alteration of feedbacks have strong effects on the magnitudes of carbon cycle fluxes, then projections, made without consideration of these feedbacks and their potential for changing carbon cycle processes, will produce incorrect estimates of future concentrations of atmospheric CO2. 

Predicting the effect of the terrestrial vegetation response to C02-induced climate change for a particular site involves explicit treatment of feedbacks. These are diagramed in Figure 3. The balance between decomposition + autotrophic respiration and gross primary production (GPP) determines the net storage and release of carbon to atmosphere. Climate meets each of these... 

Figure 3. Feedbacks in terrestrial ecosystem responses to C02-induced climate change. Arrows with plus signs (-I-) indicate processes that have positive effects or that increase the rates of other processes. Arrows with minus signs (—) indicate processes that have the opposite effects.

The ability to incorporate spatially explicit information that will couple these site-specific responses to global climate change is critical to summarizing the impact these site-specific feedbacks to global-scale feedbacks. 

It seems unlikely that feedbacks due to species replacement have begun since the beginning of the Mauna Loa record because compositional changes due to climate change will take decades and have not yet been documented on a wide scale. However, this fact increases the importance of such feedbacks to future trends in atmospheric CO2 when these feedbacks become important it is highly unlikely that positive and negative feedbacks will exactly cancel each other and more likely that one or the other will prevail and cause deviations from current trends in atmospheric CO2. 

Many climatically sensitive feedback processes could be described in addition to those outlined above. We have restricted our attention to processes that have potentially large effects. A large effect is defined as one that could change the current rate of atmospheric CO2 increase by at least 50% ( 1 Pg C-yr"" ). 

In its assessment of climate change, the IPCC (1990) identified five hydrosphere-related feedback mechanisms in the climate system likely to be activated by increased greenhouse gas concentrations in the atmosphere. These feedbacks are briefly described below for more detailed discussion of the climate system, refer to Chapter 17. 

E.-D. and Sala, O. E. (1996). Terrestrial biotic responses to environmental change and feedbacks to climate. In "Climate Change 1995 The Science of Climate Change" (J. T. Houghton et ai, eds), pp. 445-481. Cambridge University Press, Cambridge. 

Bonan GD. Forest and climate change forcing, feedbacks and the climate benefits of forest. Science, 2008. 320 pp. 1444—1449. 

Much of the concern over continued global climate change rests on the potential for positive feedbacks to accelerate ongoing increases in temperature, leading to (1) faster... 

In Eq. (LL), A// is the heat of vaporization of water and R is the gas constant. Thus the vapor pressure of water has an exponential dependence on temperature. This suggests that there may be a water vapor feedback associated with global climate change. If the atmosphere warms, for example due to increased greenhouse gases such as C02, increased concentrations of gaseous water are expected in accordance with Eq. (LL). The increased water vapor traps more thermal infrared radiation, warming the atmosphere further (e.g., Raval and Ramanathan, 1989 Stenchikov and Robock, 1995). 

Dixon, R. K., and D. P. Turner. 1991. The global carbon cycle and climate change Responses and feedbacks from below ground systems. Environmental Pollution 73 245—262. 

Figure 2.1. Diagram of factors controlling the main inputs and outputs of soil carbon, superimposed over a global map of soil organic carbon stocks. DOC, POC, and DIC stand for dissolved organic C, particulate organic C, and dissolved inorganic C, respectively. The background soil organic carbon (SOC) map (Miller Projection 1 100,000,000). See color insert. Reprinted from Davidson, E. A., and Janssens, I. A. (2006). Temperature sensitivity of soil carbon decomposition and feedbacks to climate change. Nature 440,165-173, with permission from Macmillan.

Davidson, E. A., and Janssens, I. A. (2006). Temperature sensitivity of soil carbon decomposition and feedbacks to climate change. Nature. 440,165-173. 

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