burning coal is a source of air pollution & using coal requires burning coal ->  using coal is a source of air pollution  using coal is a source of air pollution & pollution has a negative impact on the environment / air quality / water quality / society ->  using coal has a negative impact on an ecosystem  using coal has a negative impact on an ecosystem & a problem has a possible negative impact on a thing ->  a problem with using coal is that it has a negative impact on an ecosystem  a problem with using coal is that it has a negative impact on an ecosystem & damage has a negative impact on a thing -> a problem with using coal is that it damages an ecosystem