A study led by South African researchers examined the clothes and boots of tourists and scientists coming to Antarctica and found most were carrying plant seeds.
Alien plants already are growing on the Antarctic Peninsula and are likely to spread as the climate warms, they said.
"People in the past have been skeptical, saying, 'It's largely ice-covered so it's unlikely that plants will establish themselves,'" lead researcher Steven Chown from Stellenbosch University in South Africa told the BBC.
"[They're] forgetting that probably less than 1 percent, but still a significant area, is ice-free -- some of that's in the peninsula region, and it's been warming very quickly."
The peninsula, which runs from the antarctic continent up towards the southern tip of South America, has warmed by about 5 degrees Fahrenheit over half a century, much faster than the global average, researchers said.
"Antarctica has a native ecology -- a very well-established microbial ecology, and on the peninsula it has two species of indigenous plants," Chown said. "And it will be changed by species coming in."
Tourists tend to visit the warmest areas of Antarctica, which are also the places where seeds are most likely to survive, the researchers said.