(REUTERS) - US President Barack Obama said at the United Nations on Sunday (Sept 27) that climate change was one of the biggest challenges to global development and one that will affect every country.

Mr Obama referenced Pope Francis, who has spent the past week in the US, and said that dealing with climate change is "a moral calling."

Mr Obama's speech at the UN Sustainable Development Summit comes ahead of a looming federal budget confrontation that involves a US down payment into a key climate-aid fund, money considered vital to a climate deal in Paris this December.

Mr Obama had requested $500 million in the 2016 budget for the first tranche of its $3 billion pledge into a Green Climate Fund (GCF) that would help poorer countries make a transition to clean energy technologies and adapt to climate change. The fund receives guidance from the conference of the parties to the United Nations Framework Convention on Climate Change.