[en] While high-yield airburst weapons will inject oxides of nitrogen into the stratosphere and destroy ozone, lower yield surface-burst weapons - used, for example in a counterforce scenario - would inject a dark cloud of dirt into the troposphere in a ''darkness to noon'' effect. This phenomenon is modeled by Paul Crutzen and John Birks. The Crutzen and Birks model is recognized as the most thorough study available. Other ecological systems that are presently under study include aquatic life, life forms low on the food chain, agriculture, and social systems