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 UN's deputy secretary-general, Jan Eliasson, told reporters at the start of a three-day conference on risk reduction in Geneva.

"Natural disasters are not only becoming more frequent but are becoming more vehement," he warned.

A report last week from the UN International Strategy for Disaster Risk Reduction (UNISDR) said that losses may have hit $2.5 trillion so far this century.

The UNISDR said that the figure, which factored in national-level disasters that are not reported to the world body, was 50 percent higher than past estimates.

"So we have to think of this from the point of protecting people, and the price people pay. But we also have to think of economic losses. They are huge," said Eliasson.

"It's not only a question of improving lives for people, but a question of creating sustainable economies," he added.

UNISDR has gathered more than 4,000 people in Geneva this week to share lessons on how to reduce the impact of disasters, from governments, aid agencies and the private sector.

"Often it seems that it takes a disaster to take prevention measures," said Eliasson, underlining the benefits of investing in disaster-risk reduction.

He pointed to personal experience of dealing with the aftermath of a cyclone that struck Bangladesh in 1991, drowning 191,000 people in less than an hour.

Bangladesh has since become a model for the risk-reduction sector thanks to its early-warning systems and shelters, and last week's Cyclone Mahasen claimed 48 lives despite wrecking tens of thousands of homes.

"By investing in disaster-risk reduction, we are laying the basis for better development," he noted, adding that this helped the poor, who bear the brunt of catastrophes in any nation, whether developing or developed.

Experts repeatedly have warned that extremes like last year's Hurricane Sandy in the Caribbean and United States could strike more often due to climate change, as rising global temperatures send weather patterns askew and governments wrangle over reining in emissions of greenhouse gases which are blamed for the phenomenon.

"Changes that are taking place, and that we're concerned about, include an increase in heatwaves, both in intensity and frequency, increase in extreme precipitation events and also extreme sea-level related impacts because of the increase in Arctic sea level," said Rajendra Pachauri, head of the UN-backed Intergovernmental Panel on Climate Change.

"Essentially, we have to put in place adaptation measures. Because whenever we have taken action, the measures reduce losses," Pachauri told reporters.

"But neither adaptation nor mitigation will be adequate for minimising the risks of climate change. Let's not lose sight of the fact that to deal with this challenge we also have to mitigate the emissions of greenhouse gases," he said.