To cool down on hot days, consider lowering your windows. That probably has a lower carbon footprint than using the air-conditioner when driving at low speeds. The picture is less clear at higher speeds because of drag, especially if you drive a modern car with efficient AC.

If you follow these tips, you won’t need to fill up as often. But when that time comes, bear in mind that not all engines are created equal and the one in your car is optimized for a particular type of fuel. You should use it. If the manufacturer recommends regular gasoline, for example, using mid-grade or premium would be less efficient.

Finally, consider walking, biking or taking the bus when feasible. That won’t always be an option. But, sometimes, it might be. Roughly 20 percent of all vehicle trips in the United States are under a mile.

“When you get into the car, the first question that you need to ask yourself is: Do I really need to drive there,” Mr. Cooke said. “If everyone was to cut just 10 percent of the car trips they take, that would lead to a pretty significant reduction in emissions.”