The United Nations refugee agency UNHCR has said climate-related migration must be prioritised in a climate deal currently being negotiated at the Paris climate summit.

Projections by leading climate scientists of rising sea levels, heatwaves, floods and droughts linked to global warming, are likely to oblige millions of people to move out of harm's way, with some never able to return. UNHCR climate change officer Marine Franck told a news conference on the sidelines of the United Nations-sponsored COP21 climate summit in Paris on 2 December, that climate-related displacement was not a future phenomenon but already a reality.

"Since 2008 at least 22.5 million people have been displaced every year on average by the impacts of floods, storms and other climate and weather-relate events. This is the equivalent one person being displaced every second," she said.

Data from the Internal Displacement Monitoring Centre (IDMC) in Geneva shows that 22 million people were displaced by extreme events in 2013, led by Typhoon Haiyan in the Philippines, three times more than the number displaced by conflicts. In many other years, the ratio was much wider. In the early 1970s, the total number of people displaced was only about 10 million. Extreme events also include earthquakes and tsunamis, unrelated to the weather.

Negotiators from 195 countries are currently working on a draft text for a global climate deal that still runs to more than 50 pages and is riddled with sticky issues to be settled. Franck said the issue of human mobility had to be a priority.

"The Paris agreement must address human mobility. In the current draft of the negotiations the issue is addressed under 'loss and damage', but it's also important to address this issue under adaptation, preventing and minimizing displacement must be a priority," she said.

"Increasing resilience of communities so that they can remain safely in their homes. For example, storm-resistant buildings, drought-resistant crops and other adaptation measures. Enabling people to migrate in dignity, to seek alternative opportunities when living conditions deteriorate and crisis comes knocking at their door is also an important measure. Thirdly, as a last resort, carefully planning with communities for their relocation to new homes in safer areas," Franck said.

Sea level rise of 19cm since 1900, caused by factors including a thaw of glaciers from the Andes to the Alps and of Greenland's ice sheet, aggravates storm surges in many coastal regions, according to the UN panel of climate experts.

The panel's scenarios point to a further rise of 26-82cm by the late 21st century. The panel says it is at least 95 per cent probable that human activities, led by burning of fossil fuels, are the main cause of warming.