UN Secretary-General Antonio Guterres calls it the defining issue of our time: climate change is moving to the center stage at the United Nations, three years after the Paris agreement went into force. A major UN push for progress on climate change kicks off next week when Guterres travels to New Zealand and several Pacific islands, where rising sea levels are threatening the very existence of those small countries. The stepped-up diplomacy will culminate with a climate action summit at the United Nations in September, an event billed as a last chance to prevent irreversible climate change. “We are still losing the battle,” Guterres told reporters last week. “Climate change is still running faster than we are, and if we don’t reverse this trend, it will be a tragedy for the whole world.” In Fiji, Tuvalu and Vanuatu, Guterres will meet with families whose lives have been upended by cyclones, flooding and other extreme weather events. Pacific island countries face an especially dire risk from climate change because of sea level rise. In some cases, low-lying countries could disappear completely. Fiji is working to build a coalition of more than 90 countries from the Caribbean, Africa and Asia facing climate crisis. “We hope that the secretary-general will draw far more inspiration from his first visit to go further, faster and deeper with the climate summit,” Fiji’s UN Ambassador Satyendra Prasad told AFP. “We are very hopeful that the climate summit will mark a turning point.” China: climate power The UN push on climate change is shaping up amid geopolitical shifts: the United States under Donald Trump has decided to pull out of the Paris agreement to combat global warming, giving China more space to assert its views. “The Trump administration’s disdain for climate diplomacy has left China looking like the main guarantor of the Paris agreement,” said Richard Gowan, UN director for the International Crisis Group. “While China is increasingly active across the UN, other states are suspicious of its stances on human rights and development. But it is the indispensable power in climate talks now.” Trump announced in 2017 that the United States would exit the Paris agreement, but under the terms of the deal the withdrawal will only become effective in 2020. The US administration is not taking part in summit preparations but has not said it will skip the event, according to UN officials. Guterres’ mission may also be further complicated by Trump’s nomination of Kelly Knight Craft as UN ambassador.