Freak January thaws, thunder storms in March; it is predicted that this year will go down as the hottest since modern record-keeping began, thanks not only to greenhouse-gas climate change but also to the El Nino cyclical warming of the Pacific Ocean. The weird-weather factor makes the story of South America's Pacific coast Sican people and their rise and fall, all the more chilling. The Sican are the subject of Ancient Peru Unearthed: Golden Treasures of a Lost Civilization, a major exhibition organized by Peru's Sican National Museum and Calgary's Nickle Arts Museum, which opens in expanded form today at the Royal Ontario Museum in Toronto.

North Americans are more familiar with the Sican than we think. Because Spanish conquistadors melted down most of the gold treasures of the Inca (the Sican's successors), 80 per cent of "Incan" gold artifacts in museums are in fact of Sican workmanship.

The Sican people fished, farmed, traded, mined, built temples and sacrificed other humans in the worship of a bird-faced god 1,100 years ago in the Lambayeque region of northern Peru. They buried their priest-leaders in shaft tombs, some 10 to 20 metres underground, where they remained relatively safe from European predators.

Alas, even the shaft tombs didn't escape looting; the ROM's own Sican material, acquired in the 1920s at auctions in Europe, likely came to market via grave robbers. Into the 1960s, Peruvian ranchers who owned Batan Grande, the land on which the major Sican ceremonial centre once stood, were using bulldozers to hunt for ancient objects.

Still, fantastic discoveries are still being made in Lambayeque, in part thanks to El Nino. In 1975, looters uncovered what's now known as the East Tomb shaft. They got down 10 metres, but cyclical rains had flooded the depths, and the robbers had to turn back. It wasn't until 1991 that the shaft was dry enough for a team led by Japanese archeologist Izumi Shimada to excavate what turned out to be the tomb of the Sican Lord, the human embodiment of the Sican deity.

"Batan Grande is one of the heaviest looted sites in the world, so in this show we want to emphasize the importance of excavation," says Justin Jennings, the ROM's associate curator of world cultures and a veteran Peru archeologist of just 33 years of age.

The Sican Lord's remains were found in fetal position, his decapitated head positioned nearby, facing west. Also nearby were the skeletons of two women. The legs of one were splayed, as if giving birth; the other woman was positioned as if ready to catch the newborn.

Some 600 kilograms of gold and gold-alloy artifacts were found in the East Tomb; of 122 objects in Ancient Peru Unearthed, 107 are from the tomb of the Sican Lord, including his ceremonial masks, his 90-centimetre gloves of gold alloy and copper, his collection of ear spools, huge discs that hung from his extended earlobes, and gold crowns.

These crowns contain sockets so that additional headdress pieces, including gold feathers and brilliant bird plumes, could be added. Jennings estimates that when completed, headdresses could be two metres high. Many pieces have pendant or movable parts (a vampire bat head has a gold tongue that flicks when jiggled). All suggests that Sican pageantry was a thing of shimmering lights, tinkling bells and astonishing beauty.

If the excavation's story is dramatic, what archeologists learned about the collapse of Sican civilization is even more so. "It was climate change, a mega-Nino," says Victor Curary, archeologist and curator with the Sican National Museum, who was in Toronto last week to help install the show. Around the year 1080, a 30-year drought descended. Ocean currents shifted, and the fish vanished. Then came torrential rains, and the river that had once flowed near the Sican ceremonial site changed course, to bisect the holy place.

Jennings calls this a catastrophe "of Biblical proportions." He speaks of images of the Sican deity, a knife in one hand, a human head in the other, standing astride a sea teeming with fish - clearly a god in charge of controlling the power of nature and assuring abundance. "The god was great as long as the weather was good. But after 1100 AD, you no longer see representations of the Sican deity."

The Batan Grande temple complexes were burned. And with the collapse of faith, Jennings says, the people lost a motive for their prodigious manufacture of treasures. "The pressure to produce all the gold and bronze made sense as long as the deity was delivering," he says. "But as soon as you begin to doubt the system..."

Ancient Peru Unearthed marks the first major tour of Sican treasures in North America. The exhibition came to Calgary because Carlos Elera, the director of the Sican Museum (and Curary's boss) did his PhD at the University of Calgary and is fond of the place. There's another reason, explains Curary: "Machu Picchu is full of tourists! So the Peru government wants people to know of another beautiful site, to come and visit Lambayeque. Our museum is new, our beaches are beautiful and our weather is good."

Except, as the Sican people learned, when the weather gods grow angry.