LIMA, Peru — Shortly before 2 a.m. on Sunday, after more than 36 straight hours of negotiations, top officials from nearly 200 nations agreed to the first deal committing every country in the world to reducing the fossil fuel emissions that cause global warming.

In its structure, the deal represents a breakthrough in the two-decade effort to forge a significant global pact to fight climate change. The Lima Accord, as it is known, is the first time that all nations — rich and poor — have agreed to cut back on the burning oil, gas and coal.

But the driving force behind the new deal was not the threat of sanctions or other legal consequences. It was global peer pressure. And over the coming months, it will start to become evident whether the scrutiny of the rest of the world is enough to pressure world leaders to push through new global warming laws from New Delhi to Moscow or if, as a political force, international reproach is impotent.

The strength of the accord — the fact that it includes pledges by every country to put forward a plan to reduce emissions at home — is also its greatest weakness. In order to get every country to agree to the deal, including the United States, the world’s largest historic carbon polluter, the Lima Accord does not include legally binding requirements that countries cut their emissions by any particular amount.