Pledges made by countries to slash carbon emissions are deeply inadequate to take them down to safe levels by 2030 and put the brakes on global warming, a new analysis warned Monday.

Based on the stated undertakings of the world's major emitters, global emissions could reach about 57-59 billion tonnes of carbon dioxide equivalent (GtCO2e) by 2030, said the report co-authored by British academic Nicholas Stern, a former World Bank vice-president considered an authority on the economics of climate change.

The UN Environment Programme (UNEP) has calculated that emissions must fall to about 32-44 GtCO2e by 2030 for a 50-66 percent chance of reaching the goal to limit average global warming to two degrees Celsius (3.6 deg Fahrenheit) over pre-Industrial levels.

In 2010, the latest year for which a comprehensive assessment is available, global emissions were about 50 GtCO2e.

The new report by Stern and colleagues at the London School of Economics and Political Science (LSE) said the goals of the United States, European Union and China, placed them on target for a joint output of 20.9-22.3 GtCO2e in 2030.

The three countries are responsible for nearly half the world's emissions.

In order to meet the UNEP's upper limit of 44 GtCO2e by 2030, the rest of the world's nations would therefore have to emit no more than about 23 GtCO2e, said the report -- yet current and planned policies point to a level of some 35 GtCO2e.

This meant that the world faced "a significant probability of global warming of more than 2 degrees," paper co-author Bob Ward, policy director of the LSE's Grantham Research Institute on Climate Change and the Environment, told AFP by email.

The world's nations are negotiating a global climate pact that will seek to limit global warming by limiting emissions of planet-warming greenhouse gases, mainly from mankind's voracious burning of fossil fuel.

National pledges, called "intended nationally determined contributions" (INDCs), are the heart of the agreement that is meant to be sealed at a global summit in Paris in December, and take effect form 2020.

So far, the EU bloc, US, Switzerland, Norway, Mexico, Gabon, Russia, Liechtenstein and Andorra have submitted their plans.

The US has pledged to reduce emissions by 26-28 percent from 2005 levels by 2025, while the EU is targeting a 40-percent cut by 2030 on levels from 1990.

China, which accounts for about 25 percent of global emissions, has not made a formal pledge, but has set a target date of about 2030 for its emissions to peak.

Another major emitter, Russia, has said it could cut emissions 25-30 percent by 2030 over 1990 levels -- on certain conditions.

"There is a gap between the emissions pathway that would result form current ambitions and plans, and a pathway that is consistent with the global warming limit of 2C," said the report.

"Consequently, countries should be considering opportunities to narrow the gap before and after the Paris summit."

According to the UN's Intergovernmental Panel on Climate Change (IPCC), the global mean temperature could rise by up to 4.8 C this century alone, a recipe for worse drought, flood and rising seas.