Marshall Islands President Christopher Loeak was forced to heightened the seawall protecting his home last year but says the year-old defences are now barely enough to protect his family from a "climate emergency".

"Out here in the middle of the Pacific Ocean, climate change has arrived," Loeak said in the video to be released globally Friday, ahead of UN Secretary General Ban Ki-moon's climate summit in New York City next week.

Standing outside his home in the capital Majuro next to the heightened seawall, Loeak tells the camera that it is "barely enough to protect my family from the encroaching waves".

"For the Marshall Islands and our friends in the Pacific, this is already a full-blown climate emergency," Loeak said.

He will join more then 100 heads of state at the September 23 forum which he hopes will galvanise support to build "the greatest climate change alliance" the world has seen.

The United Nations is seeking to limit global warming to two degrees Celsius (3.6 degrees Fahrenheit) over pre-industrial levels, but scientists say current emission trends could hike temperatures to more than twice that level by century's end.

While US President Barack Obama is to outline his vision for reining in greenhouse gas emissions, Chinese President Xi Jinping and Indian Prime Minister Narendra Modi are among a number of prominent world leaders who will be no-shows at next week's meeting.

UN climate envoy Mary Robinson believes the summit will see the world begin to seriously tackle global warming ahead of a crucial conference in Paris next year.

"The message from the climate summit and the message going forward to Paris is that it's not business as usual with a little bit of green attached," Robinson said recently.

Loeak's video includes clips showing Majuro residential areas inundated by tides in March this year, emphasising small island's vulnerability to rising sea levels.

"In the last year alone, my country has suffered through unprecedented droughts in the north, and the biggest ever king tides in the south," he said as the surf rumbles in the background.

"The beaches of Buoj Island where I used to fish as a boy are already under water, and the fresh water we need to grow our food gets saltier every day," he said.

While the New York summit is not a formal negotiating session, Ban has urged leaders to outline their action plan and to commit to a deal on reducing greenhouse gas emissions in Paris in December 2015.