Space travel is predicted to be the next frontier for the wealthy tourist dollar, but there are fears it could also be devastating for the planet.
A single trip aboard a SpaceX Falcon rocket has about the same carbon footprint as flying across the Atlantic 395 times, according to analysis by travel website Champion Traveler. That's equivalent to the average output of 73 cars over an entire year.
"These emissions represent a tiny fraction of the human race's yearly CO2 output," the site said in a recent post.
"But... 1000s of rockets per month carrying scientific or governmental payloads as well as a steady stream of space tourists - the environmental impact will be much greater."
At the moment, SpaceX - run by eccentric tech guru Elon Musk - sends a couple of dozen flights to space a year, but plans to ramp that up dramatically. And SpaceX isn't the only company hoping to cash in on space tourism, with Richard Branson's Virgin Galactic and Jeff Bezos' Blue Origin at various stages of development.
"This reporting is not meant as a nay-say on rocket launches or space travel in general," Champion Traveler said.
"But as rocket launches become more common and space tourism accelerates... companies such as SpaceX will need to consider the environmental impact of their launches at scale."
Musk has predicted it would take 1000 rockets to transport enough crew and cargo to set up a viable colony on Mars.
The aviation industry presently dumps about 900 million tonnes of carbon dioxide into the atmosphere every year. Each litre of gasoline burned produces about 2.3kg of carbon dioxide - each atom of carbon in the fuel combining with two oxygen atoms from the atmosphere (hence the scientific notation CO2).
New York-based environmental news site Treehugger pointed out 395 is the capacity of a Boeing 777-300, so really a single Falcon launch was only about as environmentally damaging as a single flight across the Atlantic, if the plane is full - "and they do this hundreds of times a day".
"The people who can afford these flights will all be billionaires... it is a lot more important to worry about the impact of [their] stupid private jets than it is to worry about rockets," wrote Lloyd Alter.
A study earlier this year found contrails - the watery trails left behind by planes in the cool upper atmosphere - are actually worse for the climate than carbon emissions, trapping in more heat than they reflect back into space.