For people trying to lower their carbon footprint in the world, flying is a conundrum.

It’s wonderful to visit family and see new places, but air travel is also a contributor to the carbon dioxide emissions that cause global warming.

Commercial airplanes and large business jets make up about 10% of US transportation emissions, accounting for 3% of the nation’s total greenhouse gas production, according to the latest numbers from the Environmental Protection Agency.

So climate-conscious travelers may be tempted to buy an add-on to their ticket that claims to reduce the environmental impact of their flights. Several major U.S. airlines offer to let passengers buy these offsets through their websites. And multiple other companies and non-profits also sell carbon offsets.

What’s the would-be green traveler to do? Well, it’s complicated…

How bad is flying for climate change?

Flying takes a lot of energy, which means releasing carbon dioxide into the atmosphere. Creating the thrust necessary to push a 300,000 pound airplane 35,000 feet above the Earth, keep it there for a couple of hours and then bring it down safely takes a lot of jet fuel. And jet fuel is basically kerosene.

If you want to know just how much greenhouse gas your flight is putting into…