Mexico's two remaining glacial fields hold some of the world's few tropical glaciers, which are also found in South America, Africa and Papua New Guinea but are melting fast as world temperatures rise.

The rise in temperatures has accelerated in recent decades and most scientists believe the use of fossil fuels is to blame.

Glaciers are massive, slow-moving rivers of ice and in the tropics can only exist on the cold peaks of tall mountains. Most tropical glaciers, like those in Mexico, are much smaller than their cousins closer to the poles.

Scientists say glacial melt in the tropics could hit farmers and cities across Latin America by reducing water availability and hydropower generation.

On Iztaccihuatl, a dormant volcano and one of two white-capped peaks that can be seen from Mexico City, glaciers have shrunk about 70 percent since 1960, according to University of Zurich glaciologist Christian Huggel.

"Iztaccihuatl's glaciers are doomed to death," said Huggel, who studies tropical glaciers around the world.

The Aztecs, whose pyramid-building civilization was toppled by Spanish invaders in the 16th century, likened Iztaccihuatl's year-round snow cap to a veil on a princess who died of sorrow after hearing that her warrior lover had perished in battle.

The warrior returned, however, to keep vigil over her body and the Aztecs imagined him as the nearby volcano Popocatepetl.

Scientists say global warming helped send Popocatepetl's own glaciers into oblivion around 2000, although volcanic eruptions during the 1990s had made them melt even faster.

The glaciers on Iztaccihuatl could disappear by 2020, Huggel said.

Another pack of glaciers atop Pico de Orizaba, a dormant volcano 18,490 feet (5,635 meters) high in the state of Veracruz, will likely outlast those on Iztaccihuatl because of their extreme height, Huggel said.

The mountain, known as Citlaltepetl or "Star Mountain" in the Aztecs' Nahuatl language, is the third-tallest in North America. Its snowy summit was said by Aztecs to be where the deity Quetzalcoatl, a feathery serpent, had his funeral pyre.