Chlorine loading of the stratosphere as a result of the use of chlorofluorocarbons (CFCs) and related halons has increased during the last century and led to the formation of the
'ozone hole' (WMO, 2003). As a result of several international agreements the use of these compounds is now banned and levels of chlorine precursors are predicted to stabilize in the atmosphere between 2010 and 2020. Hence, the role of chlorine as a CH4 sink in the stratosphere is expected to decrease in the future. In the troposphere it is very difficult to predict future chlorine impacts. For example, a change in wind speed and wind direction patterns will change the loading of sea salt into the atmosphere and hence the production of chlorine. Changes in ocean pH and circulation will affect marine organism populations that produce organochlorine species, which are transferred from the ocean to the atmosphere. Therefore, it is impossible to gauge the future trend with any certainty.
Predictions from climate models suggest that a warming of the lower atmosphere will lead to a cooling of the mid and upper stratosphere, which will in turn decrease the efficiency of natural catalytic cycles that destroy ozone. Under these conditions, stratospheric ozone levels will increase in the mid and upper stratosphere and hence the level of O(1D) too will increase. There are many other factors that must be taken into consideration before a definitive prediction can be made on the future impact of O(1D) on stratospheric CH4, but an increase in [O(1D)] will decrease the CH4 lifetime.
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Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.