The past composition of the global atmosphere has changed dramatically as a result of periods of global cooling (accompanied by glaciation), the shifting of eco-systems as a result of (e.g.) sea-level rise/fall and volcanic/geological events. By analysis of the composition of small pockets of air trapped in ice-cores, scientists have been able to determine the long-term fluctuations in important greenhouse gases and thus piece together a history of the long-term changes (oscillations) which have occurred. Moreover, the most recent coupled climate models which account for the interaction of the atmosphere, biosphere and oceans can perform simulations on long timescales that can then be used to determine the most likely causes of the variation in these important greenhouse gases. One such gas is methane (CH4), where natural emission sources are thought to be dominant. It has been proposed that the fluctuation in the total area and latitudinal location of wetlands, where biological activity acts as the source, has played an important role in moderating atmospheric CH4 concentrations during the Last Glacial Maximum (LGM). By analyzing the output of an ensemble of Paleoclimate models involved in the Paleoclimate Modelling Intercomparison Project (PMIP2), scientists in KS-CK have correlated the strength of CH4 emissions against important climatic variables such as water table depth, soil temperature and plant productivity. They found that although strong cooling occurred in the boreal regions, the temperature decrease over wetlands was less intense. Moreover, the southward migration of wetlands during the LGM resulted in this emission source remaining an important source term, where additional wetlands formed on the exposed continental shelves in the tropics. The figure below shows the change in the length of the emission season (i.e. biological activity) for the Earth’s surface from 6 of the participating climate models. In general it can be seen that most models predict a reduction in the emission of CH4 by vegetation in the Northern Hemisphere, with an increase in South America and Africa. Therefore, reductions in plant productivity were found to be as important as the reductions due to lowering temperatures.

The results of this work is currently in press and will appear in the Journal of Geophysical Research, where a copy of the related article is given below.