Passage Summary: Since the stuff that causes acid rain is being pumped into the air less often than it used to be, the environment should start seeing less damage from acid rain.

Conclusion: The negative environmental impacts of acid rain are expected to decline globally.

Reasoning: Acid rain is caused by acidic pollutants, and the total amount of these pollutants released into the atmosphere has been dropping for several decades.

Analysis: The columnist assumes a direct, proportional relationship between the amount of pollutants and the severity of environmental damage. To weaken this, we could suggest that the remaining pollutants are more concentrated, or that the environment has reached a tipping point where even less acid causes more harm. Since this is an 'EXCEPT' question, four choices will undermine this link, and the correct one will either support it or be irrelevant. Keep an eye out for factors that could keep acid rain damage high despite lower emissions.