The world needs to wake up to the risk of a spike in natural disasters linked to climate change and strive to find ways to cut the human and economic cost, the United Nations warned on Tuesday.

"We live in a time of huge natural disasters which are made worse by climate change," the U.N.'s deputy secretary-general, Jan Eliasson, told reporters at the start of a three-day conference on risk reduction in Geneva.

Early humans living in South Africa made cultural and industrial leaps in periods of wetter weather, said a study Tuesday that compared the archaeological record of Man's evolution with that of climate change.

Anatomically modern humans, Homo sapiens, first made their appearance in Africa during the Middle Stone Age which lasted from about 280,000 to 30,000 years ago.

The first-ever manned airplane that can fly by day or night on solar power alone was set to soar early Wednesday on the second leg of its journey across the United States.

The fuel-free plane was due to leave Phoenix, Arizona for Dallas, Texas, organizers said. The U.S. crossing is being billed as the plane's first cross-continent flight.

A shipment of 259 elephant tusks smuggled out of Africa has been seized in the United Arab Emirates, the International Wildlife Fund for Animal Welfare said Tuesday.

The tusks were discovered at a Dubai port in a container shipped from Mombasa, Kenya labelled as wooden furniture.

Tornados, among the most violent of atmospheric storms, rarely reach the size and brutality of the twister that swept through an Oklahoma City suburb on Monday, experts say.

And seldom do they hit built-up areas.

An Australian zoo said Tuesday the birth of a southern white rhinoceros was a "sign of hope" for the species given the escalation of poaching in Africa.

Taronga Western Plains Zoo said the yet-to-be-named male calf was born to first-time mother Mopani in the safari-style animal park in Dubbo, 400 kilometres (250 miles) west of Sydney, on May 14.

A climber from Bangladesh and another from South Korea have died on Mount Everest as hundreds flock to the world's highest peak during good weather, Nepalese tourism officials said Tuesday.

"Both men died while descending from the summit on Monday," an official with the tourism ministry told AFP from Everest Base Camp.

Hong Kong on Monday launched a ten-year plan to reduce waste by 40 percent per person as part of efforts to catch up with other leading Asian cities and avert a looming environmental crisis.

With a population of more than 7 million, the city currently sends 1.27 kg (2.8 pounds) per person per day to three huge outdoor landfill sites which are set to reach capacity by 2020.

Mirjana Filipovic is still haunted by the land mine blast that killed her boyfriend and blew off her left leg while on a fishing trip nearly a decade ago. It happened in a field that was supposedly de-mined.

Now, unlikely heroes may be coming to the rescue to prevent similar tragedies: sugar-craving honeybees. Croatian researchers are training them to find unexploded mines littering their country and the rest of the Balkans.

A number of mice and eight gerbils sent into space in a Russian capsule destined to find out how well organisms can withstand extended flights perished during their journey, scientists said Sunday as the month-long mission touched back down on Earth.

Most of the 45 mice sent into orbit -- along with the gerbils and 15 newts -- died on the mission, which nevertheless returned with data that scientists hope will pave the way for a manned flight to Mars.