Some of the world's leading experts on oceans and climate change are meeting in Paris this week to discuss why oceans are rising, and where to channel scarce research funds to study the phenomenon.
Most scientists agree on one thing that global warming is a key reason why the world's oceans and seas are rising. And most experts believe emissions of heat-trapping greenhouse gasses are to blame. But just how fast these water bodies are rising, and how extensive the impact will be, is a matter of debate.
John Church, a leading Australian oceanographer who chairs a scientific committee at the World Climate Change Research Program, headquartered in Geneva, is among some 160 researchers who are debating these issues at a three-day conference in Paris.
"Firstly, sea level is rising now. It will continue to rise during this century. And unless we take action now it will continue to rise beyond that," he said. "So ultimately, we could be talking about large rises beyond 2100 - rises measured in meters. And also that we're impacted most through climate change by extreme events. Extreme events occur now."
Church says three major factors explain rising sea levels: As global warming heats up oceans, water expands. Melting of glaciers in the Himalayas, Patagonia and Alaska also contribute to rising sea levels. And in the longer term, melting ice sheets in Antarctica and Greenland may also have an enormous impact.
A series of studies and reports paint grim scenarios of the future: Shrinking beaches and vanishing tidal habitats, coastal communities in the United States, South Africa and elsewhere threatened by flooding, and whole islands in the Pacific vanishing into the ocean.
There are already warning signs. Some eskimos in Alaskan islands are beginning to move to the mainland because of encroaching seas. And a few years ago, New Zealand agreed to take in as environmental refugees citizens of the Pacific nation of Tuvalu, who are leaving because of rising sea levels.
"Regardless of whether we reduce our emissions or not, we're still going to have to adapt to the impact of sea-level rise and climate change," continued Church. "And we can plan to retreat from parts of the coast. We can plan to protect parts of the coast - major cities for example. But we need to think ahead about what we're going to do in response to these issue - rather than allow these effects to occur."
But Church and other scientists say many governments are not moving fast enough to plan and adapt for the future. And in many cases, research funds to study sea level rise have been cut drastically.