WASHINGTON • The vast majority of national commitments in the 2015 Paris Agreement are inadequate to prevent the worst effects of global warming, scientists said on Tuesday, naming the world's biggest greenhouse gas emitting countries as among those that must ratchet up their efforts.

"Governments are moving in the right direction, but nowhere near enough, so hopefully they will be willing to take on much stronger commitments" at next month's United Nations climate summit in Spain, said Mr Robert Watson, lead author of the report by the non-profit Universal Ecological Fund.

The report ranked nearly 75 per cent, or 136, of the pledges as insufficient, including those by major carbon emitters China, the US and India. A dozen, by countries including Australia, Japan and Brazil, were judged only partially sufficient.

Countries at next month's summit in Madrid will hash out some details of the international pact to curb warming. Chile withdrew as host following weeks of riots protesting against inequality.

Of the 184 pledges countries made under the climate agreement, only 36 are ambitious enough to help reach the agreement's goal of keeping global warming less than 1.5 deg C above pre-industrial levels, the report said. Most of these 36 are by countries in the European Union (EU).

Mr Watson, a former chair of the UN Intergovernmental Panel on Climate Change, said the report could be read two ways: "You can read, 'my god, it is hopeless' or 'my god, this is a wake-up call'."

He estimated that even if all nations meet their existing pledges, the world would be headed for a temperature rise of between 3 deg C and 3.5 deg C, which could lead to more extreme weather, rising sea levels and accelerate the loss of plant and animal species. The report rated the EU's 28 member states as having sufficient pledges because they aim to cut emissions of greenhouse gases by at least 40 per cent below the 1990 level by 2030.

It ranked the United States as insufficient because President Donald Trump reversed his predecessor Barack Obama's climate policies and yanked the country out of the pact. The administration, which argues that the Paris Agreement would cost US taxpayers too much money, filed official paperwork on Monday to withdraw, though the formal process to exit will take a year.

China, the world's top emitter of greenhouse gases, and India also came in as insufficient because their pledges focus on carbon intensity targets, which lower emissions per unit of gross domestic product.