Plans by about 150 countries to curb greenhouse gas emissions will slow climate change this century but they need to do more to limit rising global temperatures to two degrees Celsius (3.6 Fahrenheit), the United Nations said on Friday.

Scientists say warming must be kept below 2 degrees by the end of the century to stave off the worst effects of climate change such as floods, droughts and rising sea levels.

National strategies would restrict a rise in world emissions to the equivalent of 56.7 billion tonnes of carbon dioxide per year by 2030, four billion less than expected without the extra action, from 49.0 billion in 2010, it said.

"It is a very good step... but it is not enough," U.N. Climate Change Secretariat Christiana Figures said during a presentation of the report in Bonn.

The plans, known as Intended Nationally Determined Contributions (INDCs), will be the building blocks for a U.N. deal expected at a summit set for Paris from Nov. 30 to Dec. 11 to fight global warming in the years from 2020.

Figueres' Secretariat did not formally project a likely temperature rise by 2100, because most INDCs only stretch to 2030 but she said indications from independent analysis showed the pledged reductions would limit temperatures rises at 2.7 degrees.

Almost 200 governments agreed in 2010 to limit warming to 2 degrees above pre-industrial times, meaning Paris will have to agree ways to increase action in coming years. Temperatures have already gained by about 0.9 degrees Celsius (1.6 Fahrenheit).

Figueres said negotiators in Paris would have to decide how the INDCs would be enshrined in the new agreement and how to periodically review the pledges.

"Many countries have been healthily conservative about what they have put forward," she said, adding that many countries and particularly China, are likely to achieve greater emission reductions than the targets they have put forward.

Friday's report is the most authoritative attempt to sum up the impact of INDCs and was welcomed by financial investment groups.

"Strong national plans provide the kind of vital market signals required from policy makers if investors are to curb the risk of stranded assets in the fossil fuel sector and to make the huge investments in low-carbon technologies," said Stephanie Pfeifer, chief executive of the International Investors Group on Climate Change.

Environmental groups said the report showed the Paris agreement needs to be a starting point for deeper emission cuts.

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"We insist that the Paris Agreement sets up a mechanism to get countries to further drive down emissions, without delay," said Martin Kaiser, head of international climate politics at Greenpeace.

"The world needs a clear and inspiring signal from Paris that the game is changing, that all countries are taking climate science seriously, embracing the full potential of clean, renewable energy and phasing out fossil fuels," he said in a statement. (Editing by Andrew Roche and Jason Neely)