Final answer:
The most effective measure Arnold can take to reduce his environmental impact would be to switch to a car that gets 30 miles per gallon as it will significantly decrease the fuel consumption and greenhouse gas emissions associated with his travel.
Step-by-step explanation:
The question asks which option would be the most effective measure for Arnold to lessen his environmental impact, considering his current vehicle only gets 12 miles per gallon of gas. The best option among the given choices is to switch to a car that gets 30 miles per gallon.
Driving a more fuel-efficient vehicle will significantly reduce the amount of fuel used per mile, which in turn decreases greenhouse gas emissions associated with burning gasoline. Modern cars are becoming more fuel efficient, meaning it is easier to find cars that offer good performance in terms of miles per gallon. This outweighs other options such as traveling by plane, which may seem efficient on a per-passenger basis but still relies heavily on fossil fuels with limited potential for reduced emissions compared to ground vehicles, especially when not fully occupied by passengers.