Talks on a 190-nation deal to slow global warming were on a “knife edge” early on Friday as Brazil and Japan expressed guarded hopes of ending a dispute between rich and poor about curbing greenhouse gas emissions.

Negotiators were set to work well into the early hours of the morning seeking to end a standoff over the future of the U.N.’s Kyoto Protocol, which binds almost 40 rich nations to curb emissions until 2012, before the final day of the two-week talks on Friday.