The failure of wealthy nations to deliver on short-term climate commitments could hinder the rollout of a landmark treaty, a bloc of 134 developing countries, including India and China, warned at UN negotiations in Bonn.

The diplomatic spat has underscored the difficulty of reaching a consensus at the 196-nation talks.

"If we do not respect decisions that we have made, then how can we build trust among the parties?" said Chen Zhihua, China's senior negotiator, referring to long-standing pledges by rich nations to enhance financial support and "revisit" targets for curbing greenhouse gas emissions before 2020.

"And how can we lay a good foundation for the implementation of the Paris Agreement?" he added at a press conference Thursday, flanked by diplomats from India, Iran, Nicaragua and Ecuador.

The treaty, inked outside the French capital in 2015, calls on the world to cap global warming at "well below" two degrees Celsius (3.6 degrees Fahrenheit), and even 1.5 C if possible.

With one degree of warming so far, the planet has already seen an increase in drought, deadly heatwaves and superstorms engorged by rising seas.

The pact rests on voluntary carbon-cutting pledges from virtually every country in the world.

But those pledges are not enough to keep Earth in the safe zone.

Moreover, they don't kick in until 2020, and developing nations say that's too long to wait to ramp up action.

"The science is clear: if we don't get our act together before 2020, you can forget about the 2 C and 1.5 C targets," said Paul Oquist, Nicaragua's chief negotiator at the talks.