Updated

KATMANDU, Nepal (AP) — A Nepalese Sherpa who climbed Mount Everest for a record 20th time said Tuesday that the melting of glacier ice along its slopes due to global warming is making it increasingly difficult to climb the peak.

"The rising temperature on the mountains has melted much ice and snow on the trail to the summit. It is difficult for climbers to use their crampons on the rocky surfaces," Apa told reporters after flying to Katmandu on Tuesday.

Apa, who uses only one name, reached the 29,035-foot (8,850-meter) summit on Saturday for the 20th time, beating his own previous record.

The 49-year-old first climbed Everest in 1989 and has repeated the feat almost every year since. His closest rival is fellow Sherpa guide Chhewang Nima, who has made 16 trips to the summit.

Apa said when he first began climbing Everest, there was hardly any rocky surface on the trail to the summit. Now, he says, the trail is dotted with bare rocks.

The melting ice has also exposed deep crevasses, making it dangerous for climbers.

Apa has been campaigning on global warming's negative effect on the Himalayan peaks for the past three years. In a separate environmental campaign to clean up the mountain, his Eco-Everest Expedition team has been collecting garbage from the slopes of Everest. This year the team collected 7,630 pounds (4,770 kilograms) of garbage.

Apa grew up in the foothills of Everest and began carrying equipment and supplies for trekkers and mountaineers at age 12. He moved to the United States in 2006 and lives in the Salt Lake City suburb of Draper.

Sherpas were mostly yak herders and traders living in the Himalayas until Nepal opened its borders to tourists in 1950. Their stamina and knowledge of the mountains makes them expert guides and porters.

A total of 233 climbers in 25 expedition teams from various nations have been permitted by the Nepalese government to climb Everest during the spring season from the southern face of the peak.