Even after countries raised their ambitions to cut emissions of greenhouse gases in the last 18 months, the Paris Equity Check assessment found that the United States, Canada, Australia and the European Union are working off plans that could see warming between 2.1C and 3.4C.
The policies of emerging nations including China, Russia, Saudi Arabia and Turkey are even worse -- implying catastrophic 5C heating by the end of the century.
In contrast, most of the world's poorest countries are on course to stay within the 1.5C limit, according to the assessment, which is based on peer reviewed methodology and looks at the ambition of countries' climate targets published up to November this year.
But researchers warned that poorer nations would need financial support from richer countries to maintain low-emissions development beyond 2030.
"The challenge for the global south is to stay green beyond 2030," said Yann Robiou de Pont, Lead Researcher at Paris Equity Check.
Countries have agreed to a goal to limit average warming to 1.5 degrees Celsius from pre-industrial levels, which scientists say is a safer guardrail to avoid the most dangerous impacts of climate change.
Barely 1.2C of warming to date has unleashed a crescendo of deadly and costly extreme weather, from heat waves and drought to flooding and tropical storms made more destructive by rising seas.
Currently, the world is heading for around 2.5C under current commitments and plans.
The Paris Equity Check researchers produced online interactive maps of the equity of countries' climate plans, as well as another on the warming implied by their pledges that uses peer-reviewed research updated in early November and analysis from the group Climate Action Tracker.
Henry Kokofu, special envoy from Ghana, which holds the presidency of the Climate Vulnerable Forum group of countries disproportionately affected by warming, said major polluters "must deliver and do their fair-share to slash pollution levels this decade" -- as well as support developing nations hit by increasing impacts.
"Paris Equity Check shows who they are and the additional effort they need to make in order to avoid catastrophic global damage," he said in a press statement.