As winter sets in, Washingtonians’ thoughts are likely to drift to a lounge chair somewhere in the Caribbean or out in the Pacific. Sounds good, right? I bet you don’t want anyone ruining that image by telling you how much a winter escape would harm the environment. You’re not going to like this.

Lots of people like to eco-travel to minimize their vacation’s carbon footprint. As far as I can tell, that means staying in a five-star treehouse with an infinity pool. Unfortunately, it’s the traveling part of travel that really makes the biggest impact on Earth. Transporting a family of five by private car, plane and taxi takes a toll, and staying in a hotel made of bamboo isn’t going to make that up.

Just how toxic is a long journey for the planet? It depends on how you run the numbers. You could simply estimate the amount of fuel combusted, divide by the number of passengers in the vehicle, then calculate the greenhouse gases and particulate matter that would be released into the atmosphere on a per-person basis.

But this is a severely restricted view of the environmental footprint of travel. There’s also the infrastructure that makes travel possible: highways, rails, airports, etc. All of that has to be built, maintained and expanded if we’re going to keep flitting off to warmer climes when the snow starts to fall. According to an exhaustive 2008 study by Mikhail Chester, then a doctoral candidate in civil and environmental engineering at the University of California at Berkeley, infrastructure represents 19 to 53 percent of travel-related greenhouse gas emissions, depending on the mode of travel.

Let’s consider the transportation options, taking a holistic view that includes all infrastructure requirements. Chester found that, per passenger mile, train travel releases 5.6 ounces of carbon dioxide equivalents (a unit that environmental analysts use to compare greenhouse gases of varying strength). If your holiday travel takes you from Washington to Miami — about 1,000 miles — riding the rails would account for more than 350 pounds of carbon dioxide equivalents.

Planes didn’t do as well in Chester’s study. If you’re traveling on a Boeing 737, you’re responsible for 7.4 ounces of carbon dioxide equivalents per passenger mile. For the same trip to Miami, that’s a total of 463 pounds.

Automobiles finished a distant third. An ordinary sedan in Chester’s analysis released 13.4 ounces of carbon dioxide equivalents. That’s 838 pounds of carbon dioxide equivalents between Washington and Miami.

In the end, the car trip generates more than twice as much greenhouse gas as the train journey.

Is that a lot? It depends on your frame of reference. The average home’s electricity consumption emits nearly 14,000 pounds of carbon dioxide equivalents. Driving to Miami rather than taking the train creates 485 extra pounds of greenhouse gas, or about 3.5 percent of that total. You could illuminate the average U.S. home for nearly five months before releasing that amount of greenhouse gas.

Of course, your vacation’s greenhouse gas emissions will be different based on the choices you make. Chester’s automobile data are based on the national average of 1.58 persons per car. Cramming the whole family into a fuel-efficient car would probably make the car a better option than flying, just as a plane with only a handful of passengers is especially harsh on the environment on a per passenger basis. These sorts of analyses give a general sense of the impacts and serve as a useful starting point for personal decision-making.

While taking a short trip on a train is always going to make for a lighter footprint than a long-haul flight to Tahiti — no matter where you stay — it’s worth saying a few things about those eco-resorts. The U.S. government doesn’t certify hotels as eco-friendly, and some of the private organizations offering such certifications are dubious. Although the LEED program is well respected, others are based entirely on questionnaires and documents provided by the hotel itself, with little or no independent investigation. So you’re sort of on your own.

One factor you can ask about is water use, which is among the biggest impacts hotels exact on their communities and Earth. Hotels use more than 200 gallons of water per occupied room each day but can cut their consumption sharply with a few small changes. Faucet aerators, low-flow toilets and shower heads, rinse water recycling systems on washing machines, and other upgrades can cut water use by more than a third. Ask your hotelier about these features.

The other issue is new construction. Those shiny new eco-resorts sure look nice, but one of the most consistent results of environmental analysis is that new construction is terrible. A 2008 study in the United Kingdom showed that building a new eco-friendly home emitted 55 tons of carbon into the atmosphere, compared with just 15 tons to make an existing home equally energy-efficient. So, even when it comes to hotels, it really is about reduce and reuse rather than eco-upgrade.