A Canadian astronaut on a six-month stay aboard the international space station said on Sunday it looks like Earth's ice caps have melted a bit since he was last in orbit 12 years ago.

Bob Thirsk said that there is a "very thin veil of atmosphere around the Earth that keeps us alive ... Most of the time when I look out the window I'm in awe. But there are some effects of the human destruction of the Earth as well," Reuters quoted him as saying.

"This is probably just a perception, but I just have the feeling that the glaciers are melting, the snow capping the mountains is less than it was 12 years ago when I saw it last time," Thrisk was quoted as saying. "That saddens me a little bit."

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Thirsk is visited by crewmates from America's shuttle Endeavour, who delivered a Japanese-built experiment platform, installed new batteries for the station's solar power system and stashed spare parts to keep the station operational after shuttles are retired next year after seven more flights.

The Endeavour crew is set to depart on Tuesday, following a spacewalk to rearrange power cable hookups and install TV cameras on the brand new porch of Japan's space station lab.

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The Associated Press contributed to this report.