Climate feedback

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

The complexities of land surface response and runoff generation have also presented a major obstacle to global climate modelers. Hydrologic response is linked to several important climate feedbacks (see Section 6.4.2), so imtil the hydro-logic cycle, and in particular its land surface component, can be accurately represented, there is little hope for accurate assessments of global change. 

Five components of the hydrosphere play major roles in climate feedbacks - atmospheric moisture, clouds, snow and ice, land surface, and oceans. Changes to the hydrologic cycle, among other things, as a result of altered climate conditions are then referred to as responses. Interactions with climate can best be explored by examirung potential response to a climate perturbation, in this case, predicted global warming. 

This sink, a negative climate feedback mechanism, may increase with the global-warming-intensified GWC, the increase in C02 and carbonate dust in atmosphere, reforestation/afforestation, and fertilization of the aquatic ecosystems. Using the global warming projection for the year 2100 by IPCC, it is estimated that the C02 sink by the GWC will increase by 22%, or 0.18 Pg c/a. 

Lawrence, M. G., An Empirical Analysis of the Strength of the Phytoplankton-Dimethylsulfide-Cloud-Climate Feedback Cycle, J Geophys. Res., 98, 20663-20673 (f993). 

The radiative forcing depends on the concentration change and the absorption characteristics of the atmospheric constituents both are reasonably known. Therefore, uncertainties associated with model calculated radiative forcing are much smaller than the climate feedbacks, which involve complex interactions between dynamics, physics and chemistry of the climate system. Because changes in 03 affect the Earth s climate, and changes in climate and circulation affect the 03 layer (cf. Wang et al., 1996), the development of a coupled climate-chemistry model system is needed to quantify the effect of changes in atmospheric 03. 

The climatic system involves numerous factors that intensify climatic changes with minimum forcings. The withering or death of plants, for example, may cause a decrease in evapotranspiration and hence lead to precipitation attenuation, which may further increase drought conditions. In cold-climate regions snow cover formation is accompanied by a strong increase in albedo, which favors further cooling (the so-called albedo effect ). Substantial climatic feedbacks are associated with the dynamics of thermohaline circulation. 

Rossow (2003) justly warned that attempts to isolate and describe a greater number of climatic feedbacks and to quantitatively estimate them using methods proposed earlier have become confusing and disorienting, since application of a simple linear theory consisting of many sub-systems is completely unacceptable. 

Wm 2. The concept of quasi-RF makes it possible to partially take into account the impact of climatic feedbacks, resulting in RF values of 0.28 0.32 Wm-2. 

These results reflect the radical reorganization of the climate system that took place during comparatively short periods. The Holocene seemed (compared with these changes) a period of a comparatively stable climate. There is no doubt that without climatic feedbacks the growth in GHG concentration in the atmosphere should cause climate warming. However, the actual situation is much more complicated, and to understand it, it is necessary to reliably detect and estimate the role of feedbacks. Otherwise, it is impossible to reliably predict future climate change. Since peat bogs are one of the most important sources of such information, they should be protected. 

The main difficulty in understanding the causes of climate change is connected with the impossibility of considering climatic feedbacks sufficiently reliably. Primarily, this refers to cloud-radiation feedback, direct and indirect (by the effect on radiation properties of clouds) impacts of atmospheric aerosols on climate, and the impact of the atmosphere-ocean interaction on climate formation. 

Cloud climatic feedback (with emphasis on convective clouds in the tropics). 

Heimann M, Reichstein M. Terrestrial ecosystem carbon dynamics and climate feedbacks. Nature. 2008 451(7176) 289-92. 

Roscoe H. K., Kreher K., and Friess U. (2001) Ozone loss episodes in the free Antarctic troposphere, suggesting a possible climate feedback. Geophys. Res. Lett. 28,... 

---