Final answer:
Buying local food is the choice that would reduce an environmental footprint by lowering transportation-related carbon emissions. Other effective methods include larger indoor temperature ranges, water conservation, and reduced meat consumption among other strategies.
Step-by-step explanation:
Among the options provided, the one that would reduce an individual's environmental footprint is buying local food. This practice reduces the carbon emissions associated with transportation of food items over long distances. In contrast, keeping your house at a very cold temperature in the summertime, leaving the water running, and increasing the number of airplane trips would all increase your environmental footprint. Reducing energy usage by allowing a larger indoor temperature range, conserving water, and eating less meat are additional effective strategies to lower one's environmental impact. Moreover, one could further minimize their footprint by using low-flush and composting toilets, reducing the use of air conditioning, and composting kitchen and garden waste. Additionally, planting more trees and reducing the consumption of fossil fuels are effective in cutting down greenhouse gas emissions. Whenever possible, walk or bicycle instead of driving, and opt for energy-efficient products to save energy and reduce pollution.