(NEXSTAR) – Google Flights released a new feature recently that allows prospective travelers to compare flight options not just by price, layovers or airline, but also by carbon dioxide emissions.

The estimated quantity of carbon emissions for each trip is affected by the length of the trip, the airline’s planned route and the type of aircraft – newer planes tend to pollute less, Google said. The seat you pick on the plane also has an impact.

“Emissions increase for premium economy and first-class seats because they take up more space and account for a larger share of total emissions,” said Google in an announcement of the feature.

Basically, when you’re packed like a sardine into a basic economy seat on a budget airline, you’re taking up less room, and the airline can fit more people on board. One of the only good things about flying like that is you have a smaller carbon footprint.

Some routes on Google Flights may not have estimates because of a lack of data on certain aircraft or other missing information, the company said.

Right now, Google’s estimates don’t take into account what direction the plane is heading — a potentially significant factor if flying into or with the jet stream. They also don’t consider whether or not the flight is using biofuels or other alternatives.

A route with multiple stops can often result in an increase in emissions, but it’s not always the case. Non-stop flights aren’t always less polluting, particularly on longer routes. Google said that a more fuel-efficient plane can emit less on a multiple-stop journey than an older plane on a non-stop route.

Overall, airplanes account for a small portion of emissions that cause climate change — about 2% to 3% — but their share has been growing rapidly and is expected to roughly triple by mid-century with the global growth in travel.

You can learn more about how Google calculates flights’ carbon emissions here.

The Associated Press contributed to this report.