CANBERRA, Oct 29 (Reuters) - The world must unite and take significant action now to tackle climate change that is threatening the survival of Pacific island nations, the region"s leaders said on Friday, as they prepared to travel to Scotland for a climate summit. The low-lying Pacific islands are widely seen as a main front line in the campaign against climate change as they struggle against rising sea levels. "We need concrete action now. We cannot wait until 2050, it is a matter of our survival," Anote Tong, a former president of Kiribati and twice a nominee for the Nobel Peace Prize, told Reuters. Tong has predicted his country of 33 atolls and islands that stand just metres above sea level, will likely become uninhabitable in 30 to 60 years because of inundation and contamination of its freshwater supplies.Many major polluters have vowed to intensify their carbon cuts over coming decades with some aiming for net zero carbon emissions by 2050. But Pacific Island leaders said they would demand immediate action, with an initial focus on G20 leaders, on sweeping changes. G20 leaders will meet on Friday in Rome before heading to Scotland for the U.N. climate summit, known as COP26, widely seen as critical in limiting global warming. "G20 members are responsible for around 75% of the global contribution to greenhouse gas emissions, so a strong commitment and outcome from the G20 Rome Summit will pave the way for an ambitious and successful COP26," Henry Puna, former Cook Islands prime minister and now secretary of the Pacific Islands Forum, said in a statement. "We do not have the luxury of time and must join forces urgently and deliver the required ambition at COP26 to safeguard the future of all humankind, and our planet,” Puna said. Reporting by Colin Packham Editing by Robert Birsel Our Standards: The Thomson Reuters Trust Principles.