Developing countries could face a bill of $790 billion per year by 2050 for adapting to climate change, anti-poverty agency Oxfam said Wednesday. Carbon-curbing pledges that form the cornerstone of a climate rescue pact to be sealed at a U.N. summit opening in Paris next week are insufficient, it said in a report. Current commitments from some 170 nations put the world on track to warm by 3 degrees Celsius (5.4 degrees Fahrenheit) over mid-19th century levels - a full 1 C higher than the United Nations target. Unless much more is done, developing nations will end up spending about 50 percent more on climate adaptation by mid-century than they would under a 2 C scenario, the report said."World leaders need to step up. We need further cuts to emissions and more climate funding," Oxfam Executive Director Winnie Byanyima said in a statement."The human cost of climate change must be central to discussions in Paris so we get a better climate deal for poor people," she said.In addition to costly impacts like flooding, droughts and extreme weather, developing nations' economies stand to lose $1.7 trillion annually by 2050 if warming breaches 3 C, the report says. A key test for Paris will be to include a mechanism in the pact to periodically review and improve the pledges until the 2 C goal comes into view.Countries do not agree how often reviews should be done, or whether there should be an obligation to automatically ramp up efforts. Money will be a make-or-break issue at the talks. Rich nations have pledged to muster $100 billion per year in financial support for poor countries from 2020.A U.N.-commissioned estimate showed international climate finance amounted to $62 billion in 2014. Developing nations want assurances that the flow of funding will be reliable and recession-proof. And they want assurances that money will go not only towards "mitigation" programs allowing their shift away from climate-harming fossil fuels, but also for shoring up their defences against climate impacts -- "adaptation" in climate jargon.