Alireza Shakiba - Remote sensing and GIS Dept. Earth science faculty, Shanid Beheshti Univ. Evin, Tehran, lran

One of the key questions in the current debate about global warming is what will happen to organic carbon sequestered in organic matter in soils if average mean temperatures of the Earth rise. This paper aims to study the potential effect of changes in soil temperature on organic carbon sequestered in global soils. The key to understanding the potential effects of climatic change is to study the relationships between global warming and the thermal regime of soils. If we can understand and model the thermal regime of soils, then we can begin to model the potential effects of global warming scenarios on soil organic carbon. To model and predict the temperature of soils an analytical soil temperature model was devised and applied. The model uses climate and soil data and depends on a number of assumptions. Interpolated data from a General Circulation Model (GCM) and a set of world soil data were then used to provide estimates of temperature of soils in depth of 30 em over the next 100 years under three different scenarios. Predicted soil temperatures, precipitation and world vegetation data set were used in a soil organic carbon decomposition model to study the likely effects of climatic change on organic carbon in soils. Results show that levels of organic matter in global soils will decrease as a result of an increase in global temperatures and precipitation. Results also show that different climatic zones of the Earth appear to be affected differently by global warming, Results from the research, as with climatic change modeling itself, represent only one from many possible outcomes. Results from only one GeM were studied in this study. The project results depend largely on a number of justifiable but major assumptions in the theoretical models and sets of data that were used in the study. Moreover, many environmental processes in the atmosphere, oceans and on land are not well understood. Most if not all physical attempts therefore to model the coupled effects of an atmosphere-soil system will contain significant errors. Although the results show (as with previous works) that the level of organic matter in global soils will decrease as a result of an increase in global temperatures and precipitation such an outcome is by no means certain.

Soil organic matter, global warming, climate change, soil temperature, GeM, modeling