Rising sea levels mostly caused by man-made climate change will likely leave the edges of Waikiki — and possibly more of the densely developed tourist district — underwater by the year 2100, University of Hawaii climate researchers say.

Also, in the next 100 years, Oahu’s Windward coast could become much wetter and the Leeward coast much drier, depending on how hard global leaders work to curb greenhouse gas emissions, said Axel Timmermann, a UH oceanography professor.

"It all depends," said Timmermann. "It’s our choice."

His comments came during a standing-room-only lecture Monday at UH on the Intergovernmental Panel on Climate Change’s Fifth Assessment Report (AR5), which was released this week.

Timmermann and two other UH researchers, Mark Merrifield and Shang-Ping Xie, helped write the report, which covers climate change on a global scale.

The report comes out every six years or so, and the latest version bolsters earlier assessments that the planet is rapidly warming despite recent, shorter lulls in the trend and that greenhouse gases are a key reason.

"Warming of the climate system is unequivocal, and since the 1950s many of the observed changes are unprecedented over decades to millennia," the AR5 summary states. "The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, sea level has risen, and the concentrations of greenhouse gases have increased."

Temperatures in Hawaii could warm between 0.5 degree Celsius (0.9 Fahrenheit) and 4 degrees Celsius (7.2F) in the next 100 years, causing some of the islands’ lower-lying vegetation to instead grow in the mountains, Timmermann said. The lower figure would come with a dramatic reduction of emissions to preindustrial levels, while the larger assumes current levels.

It’s still too early to say how climate change will affect Hawaii overall, but Merrifield said Monday that the islands will be particularly vulnerable to high tides and flooding as sea levels rise.

Warming oceans and melting ice could cause global sea levels to rise between 1.4 and 2.4 feet on average, said Merrifield, who directs the Joint Institute for Marine and Atmospheric Research.

However, the effects of sea rise will likely be greater than average in Hawaii because it’s closer to the equator, said Chip Fletcher, an associate dean at UH’s School of Ocean and Earth Science and Technology.

To illustrate how vulnerable Hawaii is to rising seas, Merrifield showed the audience a SOEST-produced simulation of how gradually rising tides would flood parts of Waikiki and Kaka­ako. The Ala Wai Canal would also spill into the McCully-Moiliili neighborhood.

Sea rise and ocean acidification caused by greenhouse gas emissions could also erode island beaches, Merrifield said.

"So much of our economy relies on the beaches," he said.