LIMA, Peru — Diplomats from 196 countries are closing in on the framework of a potentially historic deal that would for the first time commit every nation in the world to cutting its planet-warming fossil fuel emissions — but would still not be enough to stop the early impacts of global warming.

The draft, now circulating among negotiators at a global climate summit meeting here, represents a fundamental breakthrough in the impasse that has plagued the United Nations for two decades as it has tried to forge a new treaty to counter global warming.

But the key to the political success of the draft — and its main shortcoming, negotiators concede — is that it does not bind nations to a single, global benchmark for emissions reductions.

Instead, the draft puts forward lower, more achievable, policy goals. Under the terms of the draft, every country will publicly commit to enacting its own plans to reduce emissions — with governments choosing their own targets, guided by their domestic politics, rather than by the amounts that scientists say are necessary.