Feedback climatic

Feedback Processes Involving Marine Chemistry and Climate... 

DMS has been observed in the marine atmosphere since the early 1970s, but it was not until the mid-1980s that there was interest in this gas as being a natural source for sulfate CCN. Sulfate aerosols are, in number terms, the dominant source of CCN. The major role clouds play in the climate system leads to possible climatic implications if changes to DMS production occurred. Furthermore, the dependence of this production on environment conditions means that scope for a feedback process arises this feedback is called the Charlson hypothesis. ... 

Figure 7 Diagram of the feedback loop involving climate and planktonic production of DMS. The ( + ) under biological production of DMS in the ocean indicates the uncertainty in the direction of the net feedback loop (Taken from Bigg," with permission of Cambridge University Press)...

A number of current coupled ocean-atmosphere climate models predict that the overturning of the North Atlantic may decrease somewhat under a future warmer climate.While this is not a feature that coupled models deal with well, its direct impact on the ocean s sequestration of carbon would be to cause a significant decline in the carbon that is stored in the deep water. This is a positive feedback, as oceanic carbon uptake would decline. Flowever, the expansion of area populated by the productive cool water plankton, and the associated decline... 

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. 

One such feedback is the influence of clouds and water vapor. As the climate warms, more water vapor enters the atmosphere. But how much And which parts of the atmosphere, high or low And how does the increased humidity affect cloud formation While the relationships among clouds, water vapor, and global climate are complicated in and of themselves, the situation is further complicated by the fact that aerosols exert a poorly understood influence on clouds. 

Individual climate controls do not function in isolation from one another rather, many factors link together in complex cause-effect chains (Figure 2). Factor interactions may involve feedback loops that at one extreme amplify... 

Figure 2. Within the Earth-atmosphere system numerous feedback loops govern climate. (Reproduced with permission from ref. 31. Copyright 1974 American Association for the Advancement of Science.)...

POST ET AL. Climatic Feedbacks in the Global Carbon Cycle... 

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. 

A positive feedback between vegetation and atmospheric CO2 will occur if biomass declines. This will happen to the extent that climatic warming causes increased water stress, either through decreased precipitation or increased evap-otransporation, particularly on soils of low water-holding capacity. Decreases in soil nutrient availability, either directly caused by drought or indirectly caused by replacement with taxa with more recalcitrant litter, may further decrease the net release of carbon from the biosphere to the atmosphere. Positive feedback will also arise if the current standing biomass of trees is replaced by small trees, shrubs, and herbs that store less carbon. 

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