MODELING THE GLOBAL SOURCES AND SINKS OF RADIATIVELY ACTIVE GASES

The use of numerical models in understanding the budgets of atmospheri c trace gases is discussed. The budget of methane is calculated in a t wo-dimensional model. The contrasting behaviour of the Northern and So uthern Hemisphere reflects changes in the relative importance of emiss ions, transport and chemistry. Models can also be used to test hypothe ses. An example of such a study is presented in which it is shown that changes in stratospheric ozone could have played a significant role i n the dramatic change in methane trend observed in the early 1990s. Fi nally, use of a three-dimensional model to study tropospheric trace ga ses is introduced.