Dozens of the world's nations most vulnerable to the impacts of climate change today pledged to act to limit global temperature rise to 1.5C above pre-industrial levels and to transition to 100 per cent renewables as soon as possible.

In a high level meeting at ongoing UN climate talks in Marrakech, the 48 members of the Climate Vulnerable Forum - which include Vietnam, Costa Rica, Bangladesh and Madagascar - promised to update their nationally determined contributions (NDCs) to the Paris Agreement "as early as possible before 2020", as well as preparing mid-century low carbon development strategies.

"Without stronger climate action, we might not survive, and this is not an option," said Dr. Gemedo Dalle, chair of the forum and Ethiopian environment minister, as he urged its members to encourage other countries to also deliver the targets.

It follows the released in Marrakesh earlier this week of Canada, the US and Mexico's 2050 climate plans, and the launch of a major new initiative called the 2050 Pathways Platform, designed to support countries setting long-term climate goals.

Speaking at COP22, UN climate chief Patricia Espinosa said high ambition is needed "now more than ever". "We welcome these decisions adopted by the members of the Climate Vulnerable Forum and we assure you of our support for the implementation of this vision," she said.

Climate leaders and businesses around the world welcomed the ambitious announcement, likely one of the last major announcements at the latest round of climate talks in Morocco, which are due to end today.

Former US vice president Al Gore said the ambitious commitments "show the path forward for others" and give a "renewed optimism" that the world will meet the challenge before it in time. "Today's commitment [...] is a bold vision that sets the pace for the world's efforts to implement the Paris Agreement and move even more quickly to solve the climate crisis," he said.

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Christiana Figueres, former executive secretary of the UNFCCC, said the move highlights the need for urgent climate action, adding that the world needs to "bend the curve of emissions" by 2020 in order to limit temperature rise to 1.5C. "For this we must accelerate the shift of capital and promote radical collaboration among all stakeholders," she said in a statement. "We can do it."

World Business Council for Sustainable Development president Peter Bakker also welcomed the news. "This announcement is a vote of confidence in internationally coordinated action on climate change," he said in a statement. "Now more than ever we must continue to work together to scale up the implementation of the Paris Agreement and accelerate the transition towards the low carbon economy."

Jennifer Morgan, executive director of Greenpeace International, pointed out the move is globally significant as together the countries produce around the same amount of emissions as Russia. "To see them racing ahead and be leaders in the energy revolution is inspirational," she said in a statement.