The Italian engineer, of the European Space Agency, spoke about the issue during a press conference from the space station.

He said that changes in the appearance of the planet are noticeable from the satellite, which orbits 408 km from Earth.

"From the ISS we can make human observation and what I can say is that I have seen in my photographs and those of my companions in the last six years authentic changes," he added.

"I have seen deserts move forward and glaciers melt."

He said he will continue sharing photos on social media and warning people about the problem.

"I hope that our words and view can be shared to alarm people and really warn about the number one enemy today: global warming," he added.

"I don't know if it is possible to reverse it, but we must do everything possible to reduce and stop it."

Parmitano gave his first press conference since his arrival at the orbital station a week ago.

It is his second time on the habitable satellite after his first mission, Volare, in 2013.

The 42-year-old has been put into orbit as part of the Beyond mission, which includes experiments to pave the way for future space exploration, such as returning to the Moon or an expedition to Mars.

Parmitano was sent to the space station with American Andrew Morgan and Russian Alexander Skvortsov on July 20.

He will spend two hundred days in zero gravity and during the second half of the mission will be in charge of commanding the orbital laboratory, the first Italian to do so.

Australian Associated Press